H Mansuri-Torshizi

University of Tehran, Tehrān, Ostan-e Tehran, Iran

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Publications (4)6.47 Total impact

  • E Amin, A A Saboury, H Mansuri-Torshizi, A A Moosavi-Movahedi
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    ABSTRACT: A novel monofunctional benzyldithiocarbamate, C(6)H(5)CH(2)NHCSSNa (I), and a bifunctional p-xylidine-bis(dithiocarbamate), NaSSCNHCH(2)C(6)H(4)CH(2)NHCSSNa (II), as sodium salts, were synthesized by reaction between p-xylylenediamine or benzylamine with CS(2) in the presence of NaOH. They were characterized by spectroscopic techniques such as (1)H NMR, IR, and elemental analysis. These water-soluble compounds were examined for their inhibition of both activities of mushroom tyrosinase (MT) from a commercial source of Agricus bisporus. l-3,4- Dihydroxyphenylalanine (L-DOPA) and l-tyrosine were used as natural substrates for the catecholase and cresolase enzyme reactions, respectively. Kinetic studies showed noncompetitive inhibition of I and mixed type inhibition of II on both activities of MT. The inhibition constant (K(I)) of II was smaller than that of I. Raising the temperature from 27 to 37 degrees C caused a decrease in K(I) values of I and an increase in values of II. The binding process for inhibition of I was only entropy driven, which means that the predominant interaction in the active site of the enzyme is hydrophobic; meanwhile, the electrostatic interaction can be important for the inhibition of II due to the enthalpy driven binding process. Fluorescence studies showed a decrease of emission intensity without a shift of emission maximum in the presence of different concentrations of compounds. An extrinsic fluorescence study did not show any considerable change of the tertiary structure of MT. Probably, the conformation of inhibitor-bound MT is stable and inflexible compared with uninhibited MT.
    Journal of Enzyme Inhibition and Medicinal Chemistry 09/2009; 25(2):272-81. · 1.50 Impact Factor
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    ABSTRACT: Three iso-alkyldithiocarbonates (xanthates), as sodium salts, C3H7OCS2Na (I), C4H9OCS2Na (II) and C5H11OCS2Na (III), were synthesized, by the reaction between CS2 with the corresponding iso-alcohol in the presence of NaOH, and examined for inhibition of both cresolase and catecholase activities of mushroom tyrosinase (MT) from a commercial source of Agricus bisporus. 4-[(4-methylbenzo)azo]-1,2-benzendiol (MeBACat) and 4-[(4-methylphenyl)azo]-phenol (MePAPh) were used as synthetic substrates for the enzyme for the catecholase and cresolase reactions, respectively. Lineweaver-Burk plots showed different patterns of mixed and competitive inhibition for the three xanthates and also for cresolase and catecholase activities of MT. For cresolase activity, I and II showed a mixed inhibition pattern but III showed a competitive inhibition pattern. For catecholase activity, I showed mixed inhibition but II and III showed competitive inhibition. These new synthesized compounds are potent inhibitors of MT with K(i) values of 9.8, 7.2 and 6.1 microM for cresolase inhibitory activity, and also 12.9, 21.8 and 42.2 microM for catecholase inhibitory activity for I, II and III, respectively. They showed a greater inhibitory potency towards the cresolase activity of MT. Both substrate and inhibitor can be bound to the enzyme with negative cooperativity between the binding sites (alpha > 1) and this negative cooperativity increases with increasing length of the aliphatic tail in these compounds in both cresolase and catecholase activities. The cresolase inhibition is related to the chelating of the copper ions at the active site by a negative head group (S-) of the anion xanthate, which leads to similar values of K(i) for all three xanthates. Different K(i) values for catecholase inhibition are related to different interactions of the aliphatic chains of I, II and III with hydrophobic pockets in the active site of the enzyme.
    Journal of Enzyme Inhibition and Medicinal Chemistry 05/2007; 22(2):239-46. · 1.50 Impact Factor
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    ABSTRACT: Three new n-alkyl dithiocarbamate compounds, as sodium salts, C4H9NHCS2Na (I), C6H13NHCS2Na (II) and C8H17NHCS2Na (III), were synthesized and examined for inhibition of both cresolase and catecholase activities of mushroom tyrosinase (MT) from a commercial source of Agaricus bisporus in 10 mM phosphate buffer pH 6.8, at 293K using UV spectrophotometry. Caffeic acid and p-coumaric acid were used as natural substrates for the enzyme for the catecholase and cresolase reactions, respectively. Lineweaver-Burk plots showed different patterns of mixed and competitive inhibition for catecholase and cresolase reactions, respectively. These new synthetic compounds can be classified as potent inhibitors of MT due to Ki values of 0.8, 1.0 and 1.8 microM for cresolase inhibitory activity, and also 9.4, 14.5 and 28.1 microM for catecholase inhibitory activity for I, II and III, respectively. They showed a greater potency in the inhibitory effect towards the cresolase activity of MT. Both substrate and inhibitor can be bound to the enzyme with negative cooperativity between the binding sites (alpha > 1) and this negative cooperativity increases with increasing length of the aliphatic tail in these compounds. The inhibition mechanism is presumably related to the chelating of the binuclear coppers at the active site and the different Ki values may be related to different interaction of the aliphatic chains of I, II and III with the hydrophobic pocket in the active site of the enzyme.
    Journal of Enzyme Inhibition and Medicinal Chemistry 08/2005; 20(4):393-9. · 1.50 Impact Factor
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    ABSTRACT: Binding properties and conformational change of human growth hormone (hGH) upon interaction with Fe3+ were investigated at 27 °C in NaCl solution, 50 mM, by calorimetry and spectroscopy. UV spectroscopy indicates that thermal denaturation of hGH is an irreversible process and is accompanied by aggregation. At an optimum concentration of iron thermal denaturation of hGH becomes reversible. Results from equilibrium dialysis and isothermal titration calorimetry indicate a set of four binding sites on hGH for Fe3+. Interaction of three iron ions with hGH prevents irreversibility and aggregation. Differential scanning calorimetry confirms the UV spectroscopic finding. Domain analysis by DSC shows that in the presence of iron, there are at least two main transitions corresponding with the two groups of helices. Deconvolution of the main transitions provides two sub-transitions each, the first pair is similar, but the second pair is considerably different in the enthalpy change of unfolding. Interaction of iron ions with hGH prevents aggregation by an effect on the hydrophobicity and provides information about its structure and thermal denaturation.
    Thermochimica Acta 01/2005; 438:178-183. · 1.99 Impact Factor