J F Neault

Université du Québec à Trois-Rivières, Trois-Rivières, Quebec, Canada

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Publications (32)93.99 Total impact

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    ABSTRACT: Some oxovanadium compounds have shown potential to inhibit RNase activity, while at the same time not inhibiting DNase activity. Some vanadyl complexes also inhibit protein synthesis in rabbit reticulocytes, but induce activation of protein–tyrosine kinase. To gain an insight into the interaction of oxovanadium ions with proteins, the present study was designed to examine the bindings of VOSO4 and NaVO3 salts with human serum albumin (HSA) in aqueous solution at physiological pH with metal ion concentrations of 0.0001 to 1 mM and HSA (fatty acid free) concentration of 2% w/v. Gel and capillary electrophoresis (CE) and Fourier transform infrared (FT-IR) spectroscopic methods were used to determine the metal ion binding mode, association constant, and the secondary structure of the protein in the presence of the oxovanadium compounds. Gel electrophoresis results showed that a maximum of 20 vanadyl cations (VO2+) are bound per HSA molecule with strong (K1 = 7.0 × 107 M–1) and weak (K2 = 6.5 × 105 M–1) bindings. Similarly, capillary electrophoresis showed two major bindings for vanadyl cation with K1 = 1.2 × 108 M–1 and K2 = 8.5 × 105 M–1, whereas vanadate (VO–3) has only a weak binding affinity (K = 6.0 × 103 M–1) with HSA molecule. The VO–3 binds mainly to the lysine ε-amino NH+3 groups, while VO2+ binds possibly to the histidine nitrogen atom and the N-terminal of the α-amine residue. Infrared spectroscopic analysis showed metal ion binding results in major protein secondary structural changes from that of the α-helix (55.0 to 43–44%) to the β-sheet (22.0 to 23–26%), β-antiparallel (12.0 to 13–16%), and turn (11.0 to 17–18%), at high metal ion concentration. The observed spectral changes indicate a partial unfolding of the protein structure, in the presence of oxovanadium ions.Key words: oxovanadium, protein, binding mode, binding constant, secondary structure, electrophoresis, FT-IR spectroscopy.
    Canadian Journal of Chemistry 02/2011; 79(10):1415-1421. · 0.96 Impact Factor
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    ABSTRACT: This study was designed to determine the secondary structure of human serum albumin (HSA) in the presence of aspirin in H2O and D2O solutions at physiological pH, using aspirin concentrations of 0.0001-5 mM with final protein concentration of 2% w/v. UV-vis spectra and Fourier transform infrared (FTIR) difference spectroscopy with its self-deconvolution, second derivative resolution enhancement, and curve-fitting procedures were applied to characterize the drug binding mode, the binding constant, and the protein secondary structure in the aspirin-HSA complexes. Spectroscopic evidence showed that no aspirin-protein interaction occurs at very low drug concentration (0.0001 mM), whereas at higher drug contents (0.001-0.1 mM) the aspirin anion binding (H-bonding) is mainly through the ε-amino NH3+ group with overall binding constant of K = 1.4 × 104 M-1. At high drug concentrations (1-5 mM), acetylation of Lys-199 was observed. Aspirin binding results in protein secondary structural changes from that of the α-helix 55% (free HSA) to 49%, β-sheet 22% (free HSA) to 31%, β-anti 12% (free HSA) to 4% and turn 11% (free HSA) to 16% in the aspirin-HSA complexes..Key words: aspirin, protein, drug, binding mode, binding constant secondary structure, FTIR spectroscopy.
    Canadian Journal of Chemistry 02/2011; 78(2):291-296. · 0.96 Impact Factor
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    ABSTRACT: Taxol (paclitaxel) is an anticancer drug that interacts with microtubule proteins in a manner that catalyzes their formation from tubulin and stabilizes the resulting structures. However, in the human lung tumor cell, the concentration of paclitaxel is highest in the nucleus. Therefore, it was of interest to examine the interaction of taxol with DNA and RNA in aqueous solution at physiological pH. Capillary electrophoresis and Fourier transform infrared (FTIR) difference spectroscopic methods were used to characterize the nature of drug–DNA and drug–RNA interactions and to determine the taxol binding site, the binding constant, the sequence selectivity, the helix stability, and the biopolymer secondary structure in the taxol–polynucleotide complexes in vitro. The FTIR spectroscopic studies were conducted with taxol/polynucleotide (phosphate) ratios of 1/80, 1/40, 1/20, 1/10, 1/4, and 1/2 with a final DNA(P) or RNA(P) concentration of 12.5 mmol/L, and capillary electrophoresis was performed after incubation of taxol with polynucleotides at ratios of 1/200 to 1/12 with a final polynucleotide concentration of 1.25 mmol/L. Taxol was shown to bind to DNA and RNA at G–C, A–T, or A–U bases and the backbone PO2 group. Two types of binding were observed for taxol–DNA with K1 = 1.3 × 104 L mol–1 and K2 = 3.5 × 103 L mol–1, whereas taxol–RNA complexes showed one type of binding with K = 1.3 × 104 L mol–1. The taxol–polynucleotide complexation is associated with a partial helix stabilization and no major alterations of B-DNA or A-RNA structure. Key words: DNA, RNA, taxol, binding site, binding constant, conformation, helix stability, electrophoresis, FTIR spectroscopy.
    Canadian Journal of Chemistry 02/2011; 82(6):1112-1118. · 0.96 Impact Factor
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    ABSTRACT: Dietary constituents of fresh fruits and vegetables may play a relevant role in DNA adduct formation by inhibiting enzymatic activities. Studies have shown the important role of antioxidant vitamins A, C, and E in the protection against cancer and cardiovascular diseases. The antioxidant activity of vitamin A and beta-carotene may consist of scavenging oxygen radicals and preventing DNA damage. This study was designed to examine the interaction of calf-thymus DNA with retinol and retinoic acid in aqueous solution at physiological conditions using a constant DNA concentration and various retinoid contents. Fourier transform infrared (FTIR), circular dichroism (CD), and fluorescence spectroscopic methods were used to determine retinoid binding mode, the binding constant, and the effects of retinol and retinoic acid complexation on DNA conformation and aggregation. Structural analysis showed that retinol and retinoic acid bind DNA via G-C and A-T base pairs and the backbone phosphate groups with overall binding constants of Kret = 3.0 (+/-0.50) x 10(3) (mol.L(-1))(-1) and Kretac = 1.0 (+/-0.20) x 10(4) (mol.L(-1))(-1). The number of bound retinoids per DNA were 0.84 for retinol and 1.3 for retinoic acid. Hydrophobic interactions were also observed at high retinol and retinoic acid contents. At a high retinoid concentration, major DNA aggregation occurred, while DNA remained in the B-family structure.
    Biochemistry and Cell Biology 06/2010; 88(3):469-77. · 2.92 Impact Factor
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    ABSTRACT: This review reports the effects of several drugs such as AZT (anti-AIDS), cis-Pt (antitumor), aspirin (anti-inflammatory) and vitamin C (antioxidant) on the stability and conformation of Na,K-ATPase in vitro. Drug-enzyme binding was found to be via H-bonding to the polypeptide CO and C-N groups with two binding constants K(1(AZT))=5.30 (+/-2.1)x10(5)M(-1) and K(2(AZT))=9.80 (+/-2.9)x10(3)M(-1) for AZT and one binding constant K(cis)(-Pt)=1.93 (+/-1.2)x10(4)M(-1) for cis-Pt, K(aspirin)=6.45 (+/-2.5)x10(3)M(-1) and K(ascorbate)=1.04 (+/-0.5)x10(4)M(-1) for aspirin and ascorbic acid. The enzyme secondary structure was altered with major increase of alpha-helix from 19.9% (free protein) to 22-26% and reduction of beta-sheet from 25.6% (free protein) to 17-23% upon drug complexation indicating a partial stabilization of protein conformation. The order of induced stability is AZT>cis-Pt>ascorbate>aspirin.
    Journal of Photochemistry and Photobiology B Biology 06/2008; 91(2-3):167-74. · 3.11 Impact Factor
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    ABSTRACT: Bovine pancreatic ribonuclease A (RNase A) catalyzes the cleavage of P-O5' bonds in RNA on the 3' side of pyrimidine to form cyclic 2', 5'-phosphates. It has several high affinity binding sites that make it possible target for many organic and inorganic molecules. Ligand binding to RNase A can alter protein secondary structure and its catalytic activity. In this review, the effects of several drugs such as AZT (anti-AIDS), cis-Pt (antitumor), aspirin (anti-inflammatory), and vitamin C (antioxidant) on the stability and conformation of RNase A in vitro are compared. The results of UV-visible, FTIR, and CD spectroscopic analysis of RNase complexes with aspirin, AZT, cis-Pt, and vitamin C at physiological conditions are discussed here. Spectroscopic results showed one major binding for each drug-RNase adduct with KAZT=5.29 (+/-1.6)x10(4) M(-1), Kaspirin=3.57 (+/-1.4)x10(4) M(-1), Kcis-Pt=5.66 (+/-1.9)x10(3) M(-1), and Kascorbate=3.50 (+/-1.5)x10(3) M(-1). Major protein unfolding occurred with reduction of alpha-helix from 29% (free protein) to 20% and increase of beta-sheet from 39% (free protein) to 45% in the aspirin-, ascorbate-, and cis-Pt-RNase complexes, while minor increase of alpha-helix was observed for AZT-RNase adduct.
    Journal of biomolecular Structure & Dynamics 03/2008; 25(4):387-94. · 2.98 Impact Factor
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    ABSTRACT: Aspirin is an anti-inflammatory drug and a main source of protein acetylation that can alter enzymatic activity and protein functions. Ribonuclease A (RNase A) with several high-affinity binding sites is a possible target for many organic and inorganic molecules (Leonidas at al., [2003] Protein Sci. 12, 2559-2574). This study was designed to examine the interaction of aspirin with RNase Aat physiologic conditions. Reaction mixtures of constant protein concentration (3 mM) and different aspirin contents (0.0002-2 mM) are studied by ultraviolet-visible, Fourier transform infrared, and circular dichroism spectroscopic methods to determine the drug binding mode, the drug-binding constant, and the effects of drug complexation on the protein conformation in aqueous solution. Spectroscopic results showed one major binding for the aspirin-RNase complexes with overall binding constant of K = 3.57 x 10(4) M-1. Minor reductions in the protein alpha-helix from 15.5 to 14.1% (circular dichroism) using CDPro program and 26 to 21% (infrared) were observed on aspirin interaction. The changes are indicative of some degree of protein unfolding on drug complexation.
    Cell Biochemistry and Biophysics 02/2006; 46(1):27-33. · 1.91 Impact Factor
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    ABSTRACT: The question addressed in this study is how does the protein-DNA complexation affect the structure and dynamics of DNA and protein in aqueous solution. We examined the interaction of calf-thymus DNA with human serum albumin (HSA) in aqueous solution at physiological conditions, using constant DNA concentration of 12.5 mM (phosphate) and various HSA contents 0.25 to 2% or 0.04 to 0.3 mM. Affinity capillary electrophoresis and FTIR spectroscopic methods were used to determine the protein binding mode, the association constant, sequence preference, and the biopolymer secondary structural changes in the HSA-DNA complexes. Spectroscopic evidence showed two types of HSA-DNA complexes with strong binding of K(1) = 4.5 x 10(5) M(-1) and weak binding of K(2) = 6.10 x 10(4) M(-1). The two major binding sites were located on the G-C bases and the backbone PO(2) group. The protein-DNA interaction stabilizes the HSA secondary structure. A minor alteration of B-DNA structure was observed, while no major protein conformational changes occurred.
    DNA and Cell Biology 02/2006; 25(1):63-8. · 2.34 Impact Factor
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    ABSTRACT: The interaction of taxol with DNA has major biological importance since it is shown the presence of higher concentration of taxol in the nucleus, than in the human lung tumor cell. Therefore, in this report we examine the interaction of taxol with calf-thymus DNA in aqueous solution at physiological pH, using constant DNA concentration (25 or 1.25 mM phosphate) and various taxol/DNA (phosphate) ratios 1/200 to 1/2. Capillary electrophoresis and Fourier transform infrared (FTIR) difference spectroscopic methods are used to characterize the nature of drug-DNA interaction and to determine the taxol binding site, the binding constant, sequence selectivity, helix stability and biopolymer secondary structure in the taxol-DNA complexes in vitro. Structural analysis showed that taxol is an external DNA binder with no affinity towards DNA intercalation. The major target of taxol is A-T, G-C bases and the backbone PO(2) groups. Two bindings were observed for taxol-DNA complexes with K(1)= 1.4 x 10(4) M(-1) and K(2)=3.5 X 10(3) M(-1). The taxol-DNA interaction is associated with a partial helix stabilization and no major alterations of B-DNA structures.
    Mini Reviews in Medicinal Chemistry 04/2005; 5(3):307-11. · 2.87 Impact Factor
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    ABSTRACT: Porphyrins and their metal derivatives are strong nucleic acids binders. Some of these compounds have been used for radiation sensitization therapy of cancer and are targeted to interact with cellular DNA. Chlorophyll (Chl) binds DNA via guanine N-7 atom (major groove) and the backbone phosphate group (Neault and Tajmir-Riahi. Biophys. J. 76, 2177, 1999), whereas chlorophyllin (Chln) intercalates into A-T and G-C regions (Neault and Tajmir-Riahi. J. Phys. Chem. B. 102, 1610, 1998). This study was designed to examine the interaction of RNA with chlorophyll a and chlorophyllin in aqueous solution at physiological pH with pigment/RNA(phosphate) ratios (r) of 1/80 to 1/2. Fourier transform infrared (FTIR) and UV-visible difference spectroscopic methods were used to characterize the nature of pigment-RNA interaction and to establish correlation between spectral changes and the pigment binding mode, binding constant, RNA secondary structure and structural variations of pigment-RNA complexes in aqueous solution. Spectroscopic results showed that Chl and Chln bind RNA through G-C and A-U bases and the backbone phosphate group with overall binding constants of KChl = 1.95 x 10(5) M(-1) and KChln = 1.61 x 10(5) M(-1). The larger K value obtained for Chl-RNA complexes is attributed to the formation of more stable five or six-coordinate Mg cation in the RNA adducts, while the four-coordination Cu(II) in Chln can be more stable than that of the five or six-coordinated copper ion in the Chln-RNA complexes. Aggregation of pigment-RNA complexes occurs at high metalloporphyrin concentrations. No biopolymer secondary structural changes were observed upon pigment interaction and RNA remains in the A-family structure in these pigment complexes.
    Journal of biomolecular Structure & Dynamics 09/2004; 22(1):45-50. · 2.98 Impact Factor
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    ABSTRACT: Ribonuclease A (RNase A) with several high affinity binding sites is a possible target for many organic and inorganic molecules. 3'-Azido-3'-deoxythymidine (AZT) is the first clinically effective drug for the treatment of human immunodeficiency virus (HIV) infection. The drug interactions with protein and nucleic acids are associated with its mechanism of action in vivo. This study was designed to examine the interaction of AZT with RNase A under physiological conditions. Reaction mixtures of constant protein concentration (2%) and different drug contents (0.0001-0.1 mM) are studied by UV-visible, FTIR, and circular dichroism spectroscopic methods in order to determine the drug binding mode, the drug binding constant, and the effects of drug complexation on the protein and AZT conformations in aqueous solution. The spectroscopic results showed one major binding for the AZT-RNase complexes with an overall binding constant of 5.29 x 10(5) M(-1). An increase in the protein alpha helicity was observed upon AZT interaction, whereas drug sugar pucker remained in the C2'-endo/anti conformation in the AZT-RNase complexes.
    Biopolymers 02/2003; 72(6):435-41. · 2.88 Impact Factor
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    ABSTRACT: The Na(+),K(+)-ATPase is an integral membrane protein which transports sodium and potassium cations against an electrochemical gradient. The transport of Na(+) and K(+) ions is presumably connected to an oscillation of the enzyme between the two conformational states, the E(1) (Na(+)) and the E(2) (K(+)) conformations. The E(1) and E(2) states have different affinities for ligand interaction. However, the determination of the secondary structure of this enzyme in its sodium and potassium forms has been the subject of much controversy. This study was designed to provide a quantitative analysis of the secondary structure of the Na(+),K(+)-ATPase in its sodium (E(1)) and potassium (E(2)) states in both H(2)O and D(2)O solutions at physiological pH, using Fourier transform infrared (FTIR) with its self-deconvolution and second derivative resolution enhancement methods, as well as curve-fitting procedures. Spectroscopic analysis showed that the secondary structure of the sodium salt of the Na(+),K(+)-ATPase in H(2)O solution contains alpha-helix 19.8+/-1%, beta-sheet 25.6+/-1%, turn 9.1+/-1%, and beta-anti 7.5+/-1%, whereas in D(2)O solution, the enzyme shows alpha-helix 16.8+/-1%, beta-sheet 24.5+/-1.5%, turn 10.9+/-1%, beta-anti 9.8+/-1%, and random coil 38.0+/-2%. Similarly, the potassium salt in H(2)O solution contains alpha-helix 16.6+/-1%, beta-sheet 26.4+/-1.5%, turn 8.9+/-1%, and beta-anti 8.1+/-1%, while in D(2)O solution it shows alpha-helix 16.2+/-1%, beta-sheet 24.5+/-1.5%, turn 10.3+/-1%, beta-anti 9.0+/-1%, and random coil 40+/-2%. Thus the main differences for the sodium and potassium forms of the Na(+),K(+)-ATPase are alpha-helix 3.2% in H(2)O and 0.6% in D(2)O, beta-sheet (pleated and anti) 1.5% in H(2)O and random structure 2% (D(2)O), while for other minor components (turn structure), the differences are less than 1%.
    Journal of biomolecular Structure & Dynamics 11/2002; 20(2):173-8. · 2.98 Impact Factor
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    ABSTRACT: The thymidine analog 3'-azido-3'-deoxythymidine (AZT) is still one of the effective drugs against human immunodeficiency (HIV) infection. AZT has been used as inhibitor of HIV-1 reverse transcriptase, the virus encoded enzyme which catalyzes transcription of viral RNA to DNA. The drug interaction with protein has been included in its mechanism of action. Human serum albumin (HSA) is a carrier of many drugs in vivo and thus AZT-HSA complexation can serve as a model for drug-protein interaction. This study was designed to examine the interaction of AZT with human serum albumin at physiological conditions using constant protein concentration (0.2% or 2%) and different drug contents (5 to 1000 microM). Capillary electrophoresis, FTIR and CD spectroscopic methods were used to determine the drug binding mode, the drug binding constant and the effects of drug-HSA complexation on the protein and AZT conformations in aqueous solution. Capillary electrophoresis and spectroscopic results showed two major bindings for the AZT-HSA complexes with K(1)=1.9 x 10(6) M(-1)and K(2)= 2.1 x 10(4) M(-1). Minor alterations of the protein secondary structure from that of the alpha-helix to beta-sheet were observed upon drug complexation, whereas the drug sugar pucker remained in the C2'-endo/anti conformation upon protein interaction.
    Journal of biomolecular Structure & Dynamics 07/2002; 19(6):1007-14. · 2.98 Impact Factor
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    ABSTRACT: cis-Pt(NH(3))(2)Cl(2) (cisplatin) is an antitumor drug with many severe toxic side effects including enzymatic changes associated with its mechanism of action. This study was designed to examine the interaction of cisplatin drug with the Na(+), K(+)-dependent adenosine triphosphatase (Na,K-ATPase) in H(2)O and D(2)O solutions at physiological pH, using drug concentrations of 0.1 microM to 1 mM. UV absorption spectra and Fourier transform infrared difference spectroscopy with its self-deconvolution, second derivative resolution enhancement and curve-fitting procedures were applied to characterize the drug binding mode, the drug binding constant and the protein secondary structure in the cisplatin-ATPase complexes. Spectroscopic evidence showed that at low drug concentration (0.1 microM), cisplatin binds mainly to the lipid portion of the enzyme, whereas at higher drug contents, the Pt cation interaction is through the polypeptide C==O and C-N groups with overall binding constant of K=1.93 x 10(4) M(-1). At high cisplatin concentration (1 mM), drug binding results in protein secondary structural changes from that of the alpha-helix 19.8%; beta-pleated 25.6%; turn 9.1%; beta-antiparallel 7.5% and random 38%, in the free Na,K-ATPase to that of the alpha-helix 22.2%; beta-pleated 23.2%; turn 9.4%; beta-antiparallel 2.2% and random 43%, in the cis-Pt-ATPase complexes.
    Journal of Inorganic Biochemistry 10/2001; 86(2-3):603-9. · 3.20 Impact Factor
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    ABSTRACT: Ag(I) is a strong nucleic acids binder and forms several complexes with DNA such as types I, II, and III. However, the details of the binding mode of silver(I) in the Ag-polynucleotides remains unknown. Therefore, it was of interest to examine the binding of Ag(I) with calf-thymus DNA and bakers yeast RNA in aqueous solutions at pH 7.1-6.6 with constant concentration of DNA or RNA and various concentrations of Ag(I). Fourier transform infrared spectroscopy and capillary electrophoresis were used to analyze the Ag(I) binding mode, the binding constant, and the polynucleotides' structural changes in the Ag-DNA and Ag-RNA complexes. The spectroscopic results showed that in the type I complex formed with DNA, Ag(I) binds to guanine N7 at low cation concentration (r = 1/80) and adenine N7 site at higher concentrations (r = 1/20 to 1/10), but not to the backbone phosphate group. At r = 1/2, type II complexes formed with DNA in which Ag(I) binds to the G-C and A-T base pairs. On the other hand, Ag(I) binds to the guanine N7 atom but not to the adenine and the backbone phosphate group in the Ag-RNA complexes. Although a minor alteration of the sugar-phosphate geometry was observed, DNA remained in the B-family structure, whereas RNA retained its A conformation. Scatchard analysis following capillary electrophoresis showed two binding sites for the Ag-DNA complexes with K(1) = 8.3 x 10(4) M(-1) for the guanine and K(2) = 1.5 x 10(4) M(-1) for the adenine bases. On the other hand, Ag-RNA adducts showed one binding site with K = 1.5 x 10(5) M(-1) for the guanine bases.
    Biophysical Journal 10/2001; 81(3):1580-7. · 3.67 Impact Factor
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    ABSTRACT: Anions interact with protein to induce structural changes at ligand binding sites. The effects of anion complexation include structural stabilization and promote cation-protein interaction. This study was designed to examine the interaction of aspirin and ascorbate anions with the Na+, K+-dependent adenosine triphosphatase (Na,K-ATPase) in H2O and D2O solutions at physiological pH, using anion concentrations of 0.1 microM to 1 mM with final protein concentration of 0.5 to 1 mg/ml. Absorption spectra and Fourier transform infrared (FTIR) difference spectroscopy with its self-deconvolution, second derivative resolution enhancement and curve-fitting procedures were applied to characterize the anion binding mode, binding constant, and the protein secondary structure in the anion-ATPase complexes. Spectroscopic evidence showed that the anion interaction is mainly through the polypeptide C=O and C-N groups with minor perturbation of the lipid moiety. Evidence for this came from major spectral changes (intensity variations) of the protein amide I and amide II vibrations at 1651 and 1550 cm(-1). respectively. The anion-ATPase binding constants were K=6.45 x 10(3) M(-1) for aspirin and K=1.04 x 10(4) M(-1) for ascorbate complexes. The anion interaction resulted in major protein secondary structural changes from that of the alpha-helix 19.8%; beta-pleated sheet 25.6%; turn 9.1%; beta-antiparallel 7.5% and random 38% in the free Na,K-ATPase to that of the alpha-helix 24-26%; beta-pleated 17-18%; turn 8%; beta-antiparallel 5-3% and random 45.0% in the anion-ATPase complexes.
    Journal of biomolecular Structure & Dynamics 09/2001; 19(1):95-102. · 2.98 Impact Factor
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    ABSTRACT: The herbicides 6-chloro-N-ethyl-N'-(1-methylethyl)-1,3,5-triazine-2,4-diamine (atrazine) and 2,4-dichlorophenoxyacetic acid (2,4-D) are widely used in agricultural practice to fight dicotyledon weeds mainly in maize, cereals, and lucerne. As a result, these compounds are found not only in the plants, soil, and water, but also in the cultivated ground in the following years as well as in agricultural products such as fruits, milk, butter, and sugar beet. The toxicological effects of herbicides occur in vivo, when transported to the target organ through the bloodstream. It has been suggested that human serum albumin (HSA) serves as a carrier protein to transport 2,4-D to molecular targets. This study was designed to examine the interaction of atrazine and 2,4-D with HSA in aqueous solution at physiological pH with herbicide concentrations of 0.0001-1 mM, and final protein concentration of 1% w/v. Gel and capillary electrophoresis, UV-visible and Fourier transform infrared spectroscopic methods were used to determine the drug binding mode, the drug binding constant, and the protein secondary structure in aqueous solution. Structural analysis showed that different types of herbicide-HSA complexes are formed with stoichiometric ratios (drug/protein) of 3:1 and 11:1 for atrazine and 4.5:1 and 10:1 for 2,4-D complexes. Atrazine showed a weak binding affinity (K=3.50 x 10(4) M(-1)), whereas two bindings (K(1)=2.50 x 10(4) M(-1) and K(2)=8.0 x 10(3) M(-1)) were observed for 2,4-D complexes. The herbicide binding results in major protein secondary structural changes from that of the alpha-helix 55% to 45--39% and beta-sheet 22% to 24--32%, beta-anti 12% to 10--22% and turn 11% to 12--15%, in the drug-HSA complexes. The observed spectral changes indicate a partial unfolding of the protein structure, in the presence of herbicides in aqueous solution.
    Biochimica et Biophysica Acta 08/2001; 1548(1):129-38. · 4.66 Impact Factor
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    ABSTRACT: Taxol (paclitaxel) is an anticancer drug, which interacts with microtuble proteins, in a manner that catalyzes their formation from tubulin and stabilizes the resulting structures (Nogales et al., Nature 375 (1995) 424-427). This study was designed to examine the interaction of taxol with human serum albumin (HSA) in aqueous solution at physiological pH with drug concentrations of 0.0001-0.1 mM, and HSA (fatty acid free) concentration of 2% w/v. Gel electrophoresis, absorption spectra and Fourier transform infrared (FTIR) spectroscopy with self-deconvolution and second-derivative resolution enhancement were used to determine the drug binding mode, binding constant and the protein secondary structure in the presence of taxol in aqueous solution. Spectroscopic evidence showed that taxol-protein interaction results into two types of drug-HSA complexes with overall binding constant of K=1.43 x 10(4) M(-1). The molar ratios of complexes were of taxol/HSA 30/1 (30 mM taxol) and 90/1 (90 mM taxol) with the complex ratios of 1.9 and 3.4 drug molecules per HSA molecule, respectively. The taxol binding results in major protein secondary structural changes from that of the alpha-helix 55 to 45% and beta-sheet 22 to 26%, beta-anti 12 to 15% and turn 11 to 16%, in the taxol-HSA complexes. The observed spectral changes indicate a partial unfolding of the protein structure, in the presence of taxol in aqueous solution.
    Biochimica et Biophysica Acta 04/2000; 1478(1):61-8. · 4.66 Impact Factor
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    ABSTRACT: cis-Pt(NH3)2Cl2 (cisplatin) is an antitumor drug with many severe toxic side effects including enzymatic structural changes associated with its mechanism of action. This study is designed to examine the interaction of cisplatin drug with ribonuclease A (RNase A) in aqueous solution at physiological pH, using drug concentration of 0.0001 mM to 0.1 mM with final protein concentration of 2% w/v. Absorption spectra and Fourier transform infrared (FTIR) spectroscopy with its self-deconvolution, second derivative resolution enhancement and curve-fitting procedures were used to characterize the drug binding mode, association constant and the protein secondary structure in the cisplatin-RNase complexes. Spectroscopic results show that at low drug concentration (0.0001 mM), no interaction occurs between cisplatin and RNase, while at higher drug concentrations, cisplatin binds indirectly to the polypeptide C=O, C-N (via H2O or NH3 group) and directly to the S-H donor atom with overall binding constant 5.66 x 10(3)M(-1). At high drug concentration, major protein secondary structural changes occur from that of the alpha-helix 29% (free enzyme) to 20% and beta-sheet 39% (free enzyme) to 45% in the cisplatin-RNase complexes. The observed structural changes indicate a partial protein unfolding in the presence of cisplatin at high drug concentration.
    Journal of biomolecular Structure & Dynamics 09/1999; 17(1):101-9. · 2.98 Impact Factor
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    J F Neault, H A Tajmir-Riahi
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    ABSTRACT: Porphyrins and metalloporphyrins are strong DNA binders. Some of these compounds have been used for radiation sensitization therapy of cancer and are targeted to interact with cellular DNA. This study was designed to examine the interaction of calf thymus DNA with chlorophyll a (CHL) in aqueous solution at physiological pH with CHL/DNA(phosphate) ratios (r) of 1/160, 1/80, 1/40, 1/20, 1/10, and 1/5. Fourier transform infrared (FTIR) difference spectroscopy was used to characterize the nature of DNA-pigment interactions and to establish correlations between spectral changes and the CHL binding mode, binding constant, sequence selectivity, DNA secondary structure, and structural variations of DNA-CHL complexes in aqueous solution. Spectroscopic results showed that CHL is an external DNA binder with no affinity for DNA intercalation. At low pigment concentration (r = 1/160, 1/80, and 1/40), there are two major binding sites for CHL on DNA duplex: 1) Mg-PO2 and 2) Mg-N7 (guanine) with an overall binding constant of K = 1.13 x 10(4) M-1. The pigment distributions are 60% with the backbone PO2 group and 20% with the G-C base pairs. The chlorophyll interaction is associated with a major reduction of B-DNA structure in favor of A-DNA. At high chlorophyll content (r = 1/10), helix opening occurs, with major spectral alterations of the G-C and A-T bases. At high chlorophyll concentration (1/5), pigment aggregation is observed, which does not favor CHL-DNA complexation.
    Biophysical Journal 05/1999; 76(4):2177-82. · 3.67 Impact Factor