Gary Gerfen

Albert Einstein College of Medicine, New York City, New York, United States

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Publications (8)20.59 Total impact

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    ABSTRACT: The giant extracellular hemoglobin (erythrocruorin) from the earth worm (Lumbricus terrestris) has shown promise as a potential hemoglobin-based oxygen carrier (HBOC) in in vivo animal studies. An important beneficial characteristic of this hemoglobin (LtHb) is the large number of heme-based oxygen transport sites which helps overcome issues of osmotic stress when attempting to provide enough material for efficient oxygen delivery. A potentially important additional property is the capacity of the HBOC either to generate nitric oxide (NO) or to preserve NO bioactivity in order to compensate for decreased levels of NO in the circulation.. The present study compares the NO generating and NO bioactivity-preserving capability of LtHb with that of human adult hemoglobin (HbA) through several reactions including: nitrite reductase, reductive nitrosylation and, the still controversial, nitrite anhydrase reaction. An assignment of a heme bound dintrogen trioxide as the stable intermediate associated with the nitrite anhydrase reaction in both LtHb and HbA is supported based on functional and EPR spectroscopic studies. The role of the redox potential as a factor contributing to the NO generating activity of these two proteins is evaluated. The results show that LtHb undergoes the same reactions as HbA and that the reduced efficacy for these reactions for LtHb relative to HbA is consistent with the much higher redox potential of LtHb. Evidence of functional heterogeneity in LtHb is explained in terms of the large difference in the redox potential of the isolated subunits.
    The Journal of biological chemistry. 11/2014;
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    ABSTRACT: Herein are reported unique properties of the human 2-oxoglutarate dehydrogenase multienzyme complex (OGDHc), a rate-limiting enzyme in the Krebs (citric acid) cycle. (a) Functionally competent 2-oxoglutarate dehydrogenase (E1o-h) and dihydrolipoylsuccinyl transferase (E2o-h) components have been expressed according to kinetic and spectroscopic evidence. (b) A stable free radical, consistent with the C2-(C2α-hydroxy)-γ-carboxypropylidene thiamin diphosphate (ThDP) cation radical was detected by electron spin resonance on reacting of the E1o-h with 2-oxoglutarate (OG) by itself or when assembled from individual components into OGDHc. (c) An unusual stability of the E1o-h-bound C2-(2α-hydroxy)-γ-carboxy-propylidene thiamin diphosphate (the ThDP-enamine/C2α-carbanion, the first post-decarboxylation intermediate) was observed, likely stabilized by the 5-carboxyl group of OG, not reported before. (d) The reaction of OG with the E1o-h gave rise to superoxide anion and hydrogen peroxide (reactive oxygen species, ROS). (e) The relatively stable enzyme-bound enamine is the likely substrate for oxidation by O2, leading to the superoxide anion radical (in d) and the radical (in b). (f)The specific activity assessed for ROS formation compared to the NADH (overall complex) activity, as well as the fraction of radical intermediate occupying active centers of E1o-h are consistent with each other, and indicate that radical/ROS formation is an off-pathway side reaction comprising less than 1% of the on-pathway reactivity. Yet, the nearly ubiquitous presence of OGDHc in human tissues, including the brain, makes these findings of considerable importance in human metabolism, and perhaps disease.
    Journal of Biological Chemistry 09/2014; · 4.65 Impact Factor
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    ABSTRACT: Abstract There is a need for radioprotectors that protect normal tissues from ionizing radiation in patients receiving high doses of radiation and during nuclear emergencies. We investigated the possibility of creating an efficient oral radioprotector based on the natural pigment melanin that would act as an internal shield and protect the tissues via Compton scattering followed by free radical scavenging. CD-1 mice were fed melanin-containing black edible mushrooms Auricularia auricila-judae before 9 Gy total body irradiation. The location of the mushrooms in the body before irradiation was determined by in vivo fluorescent imaging. Black mushrooms protected 80% of mice from the lethal dose, while control mice or those given melanin-devoid mushrooms died from gastrointestinal syndrome. The crypts of mice given black mushrooms showed less apoptosis and more cell division than those in control mice, and their white blood cell and platelet counts were restored at 45 days to preradiation levels. The role of melanin in radioprotection was proven by the fact that mice given white mushrooms supplemented with melanin survived at the same rate as mice given black mushrooms. The ability of melanin-containing mushrooms to provide remarkable protection against radiation suggests that they could be developed into oral radioprotectors.
    Cancer Biotherapy & Radiopharmaceuticals 11/2012; 27(9):570-6. · 1.44 Impact Factor
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    ABSTRACT: Sporothrix schenckii is the etiological agent of sporotrichosis, the main subcutaneous mycosis in Latin America. Melanin is an important virulence factor of S. schenckii, which produces DHN-melanin in conidia and yeast cells. Additionally, L-DOPA can be used to enhance melanin production on these structures as well as on hyphae. Some fungi are able to synthesize another type of melanoid pigment called pyomelanin as a result of tyrosine catabolism. Since there is no information about tyrosine catabolism in Sporothrix, we cultured 73 strains, including representatives of the newly described Sporothrix species of medical interest, such as S. brasiliensis, S. schenckii, and S. globosa in a minimal medium with tyrosine. All but one strain were able to produce a melanoid pigment with a negative charge in this culture medium after nine days of incubation. A S. schenckii DHN-melanin mutant strain also produced pigment in presence of tyrosine. Further analysis showed that pigment production occurs in both filamentous and yeast phases, and pigment accumulates in supernatants during stationary phase growth. Notably, sulcotrione inhibits pigment production. Melanin ghosts of wild type and DHN-mutant strains obtained when the fungus was cultured with tyrosine were similar to melanin ghosts yielded on absence of precursor, indicating that this melanin does not polymerize on fungal cell-wall. However, pyomelanin producing fungal cells were more resistant to nitrogen-derived oxidants and to ultraviolet light. In conclusion, at least three species of the Sporothrix complex are able to produce pyomelanin in the presence of tyrosine and this pigment might be involved in virulence.
    Applied and Environmental Microbiology 10/2012; · 3.95 Impact Factor
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    ABSTRACT: Melanin, a high-molecular weight pigment that is ubiquitous in nature, protects melanized microorganisms against high doses of ionizing radiation. However, the physics of melanin interaction with ionizing radiation is unknown. We rationally designed melanins from either 5-S-cysteinyl-DOPA, L-cysteine/L-DOPA, or L-DOPA with diverse structures as shown by elemental analysis and HPLC. Sulfur-containing melanins had higher predicted attenuation coefficients than non-sulfur-containing melanins. All synthetic melanins displayed strong electron paramagnetic resonance (2.14.10(18), 7.09.10(18), and 9.05.10(17) spins/g, respectively), with sulfur-containing melanins demonstrating more complex spectra and higher numbers of stable free radicals. There was no change in the quality or quantity of the stable free radicals after high-dose (30,000 cGy), high-energy ((137)Cs, 661.6 keV) irradiation, indicating a high degree of radical stability as well as a robust resistance to the ionizing effects of gamma irradiation. The rationally designed melanins protected mammalian cells against ionizing radiation of different energies. We propose that due to melanin's numerous aromatic oligomers containing multiple pi-electron system, a generated Compton recoil electron gradually loses energy while passing through the pigment, until its energy is sufficiently low that it can be trapped by stable free radicals present in the pigment. Controlled dissipation of high-energy recoil electrons by melanin prevents secondary ionizations and the generation of damaging free radical species.
    PLoS ONE 01/2009; 4(9):e7229. · 3.53 Impact Factor
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    ABSTRACT: Given the increasing prevalence of cryptococcosis caused by Cryptococcus gattii (serotypes B and C) strains, there is a need for rapid and reliable tests that discriminate C. gattii from Cryptococcus neoformans (serotypes A, D, and AD). Seventy-two C. neoformans strains, sixty-seven C. gattii strains, and five Candida albicans strains were analyzed for their ability to grow and produce pigment on minimal D-tryptophan D-proline (m-DTDP) medium, on yeast carbon base D-tryptophan D-proline (YCB-DTDP) medium, and on fructose D-tryptophan glycine (m-FDTG) medium. Of the C. gattii and C. neoformans isolates, 94% and 0% grew on m-DTDP agar, respectively, and 98% and 0% grew in YCB-DTDP medium, respectively. C. gattii produced large amounts of brown intracellular pigment(s) on m-DTDP agar and smaller amounts of yellow-brown (amber) extracellular pigment(s). C. albicans grew on both media and produced a pink photoactivated pigment on m-DTDP agar. C. gattii produced large amounts of brown intracellular pigments on the differential medium m-FDTG, whereas C. neoformans produced smaller amounts of the brown pigments and C. albicans produced a pink pigment. The pigments produced by C. gattii from D-tryptophan were distinct and were not related to melanin formation from 3,4-dihydroxyphenylalanine. Thin-layer chromatography of the methanol-extracted C. gattii cells detected four different pigments, including brown (two types), yellow, and pink-purple compounds. We conclude that tryptophan-derived pigments are not melanins and that growth on m-DTDP or YCB-DTDP agar can be used to rapidly differentiate C. gattii from C. neoformans.
    Journal of clinical microbiology 02/2008; 46(1):255-64. · 4.16 Impact Factor
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    ABSTRACT: The human fungal pathogen Cryptococcus neoformans produces melanin in the presence of various substrates, including the L enantiomer of 3,4-dihydroxyphenylalanine (DOPA). The enzyme laccase catalyses the formation of melanin by oxidizing L-DOPA, initiating a series of presumably spontaneous reactions that ultimately leads to the polymerization of the pigment in the yeast cell wall. There, melanin protects the cell from a multitude of environmental and host assaults. Thus, the ability of C. neoformans to produce pigments from a variety of available substrates is likely to confer a survival advantage. A number of C. neoformans isolates of different serotypes produced pigments from D-DOPA, the stereoisomer of L-DOPA. Acid-resistant particles were isolated from pigmented C. neoformans cells grown in the presence of D-DOPA. Biophysical characterization showed the particles had a stably detectable free-radical signal by EPR, and negative zeta potential, similar to L-DOPA-derived particles. No major differences were found between L- and D-DOPA ghosts in terms of binding to anti-melanin antibodies, or in overall architecture when imaged by electron microscopy. C. neoformans cells utilized L- and D-DOPA at a similar rate. Overall, our results indicate that C. neoformans shows little stereoselectivity for utilizing DOPA in melanin synthesis. The ability of C. neoformans to use both L and D enantiomers for melanization implies that this organism has access to a greater potential pool of substrates for melanin synthesis, and this could potentially be exploited in the design of therapeutic inhibitors of laccase.
    Microbiology 01/2008; 153(Pt 12):3954-62. · 2.85 Impact Factor
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    ABSTRACT: Hydrogen sulfide (H2S) has been regarded as a poisonous gas with a wide spectrum of cytotoxic effects. However, a new controversial role is emerging for H2S in the chemistry of biological systems. It has been found that H2S is synthesized endogenously in mammalian tissues and that it functions as a neuromodulator, and a smooth muscle relaxant [1]. However, the reaction of H2S with Hb and Mb, in the presence of H2O2or O2, results in covalent modification of the heme pyrrole ring bearing the 4-vinyl group, generating the so-called sulfmyoglobin and sulfhemoglobin derivatives. These sulfheme derivatives have lower O2 affinity affecting the heme protein functionality, resulting in a rare blood disease called sulfhemoglobinemia. For the formation of the sulfheme complex, the presence of a heme-ferryl and RSH species are needed, in addition to the adequate oriented histidine in the heme distal site and . However, the structural transient species are not known. Analysis of the sulfheme complex to further comprehend the mechanism and action mode of H2S in the human body, as well as in other organisms is essential. Therefore, it is important to define the relationship between H2S and hemeproteins since these proteins are prime targets. Here, we focus on determining the key intermediates controlling the appropriate interactions that lead to the formation of the sulfheme protein. To accomplish this aim, EPR analysis on Myoglobin (Mb) in the presence of H2S and H2O2 or O2 was performed. The data showed bands associated with ferric low spin species. Thus, the results indicate that the final sulfheme complex is a six coordinated low spin specie. Also, the data showed the development of bands associated characteristic thiol radical bands around 2.051 g and 2.032 g values. Interestingly, the formation of the thiol radicals was not observed upon the reaction of Mb with H2S, in the absence of O2 or H2O2. These data suggests that a thiol radical is a key intermediate in the mechanism that leads to the sulfMb complex formation. As a consequence, the results produced insight into the chemistry of H2S with hemeproteins where H2S reacts as an anti-oxidant, limiting the availability of the heme ferryls species to react with nearby amino acids. Therefore, the evidence shows that a single Histidine E7 amino acid controls the selective toxicity and reactivity of H2S with different hemoglobins, limiting ROS activity with heme proteins.
    Nitric Oxide. 27:S35.