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M M Shah

Publications and source records attributed to M M Shah.

28 records · Page 2Linked to original sources
PubMed1992

On the mechanism of inhibition of the veratryl alcohol oxidase activity of lignin peroxidase H2 by EDTA.

The mechanism of inhibition of the veratryl alcohol oxidase activity of lignin peroxidase H2 (LiPH2) by EDTA was investigated. It was found that EDTA was decarboxylated and that cytochrome c, nitro blue tetrazolium, ferric iron, and molecular oxygen were reduced in a reaction mixture containing LiPH2, H2O2, veratryl alcohol, and EDTA. The reductive activity observed with LiPH2 followed first order kinetics with respect to the concentration of EDTA. Stoichiometry studies showed that in the presence of sufficient EDTA, 1.7 mol of ferric iron were reduced per mole of H2O2 added to the reaction mixture. Superoxide- and EDTA-derived radicals were detected by ESR spin trapping upon incubation of LiPH2 with H2O2, veratryl alcohol, and EDTA. The Km values of veratryl alcohol and H2O2 remained the same for both the oxidative and reductive activities of LiPH2. Reductive activity was also observed with LiPH2 and EDTA using other free radical mediators in the place of veratryl alcohol, such as 1,4-dimethoxybenzene, 1,2,3- and 1,2,4-trimethoxybenzenes, and 1,2,4,5-tetramethoxybenzene. EDTA reduced the cation radical of 1,2,4,5-tetramethoxybenzene formed by LiPH2 in the presence of H2O2. Hence, it is proposed that the apparent inhibition of the veratryl alcohol oxidase activity of LiPH2 by EDTA is due to the reduction of the veratryl alcohol cation radical intermediate back to veratryl alcohol by EDTA. The reduction of cytochrome c, nitro blue tetrazolium, ferric ion, and molecular oxygen appears to be mediated by the EDTA radical formed by reduction of the veratryl alcohol cation radical.

Alcohol Oxidoreductases↗
PubMed1992

Use of white rot fungi in the degradation of environmental chemicals.

White rot fungi have been shown to mineralize a wide variety of environmental pollutants. These fungi secrete a number of enzymes that are involved in its unique ability to degrade lignin, the structural component of woody plants. Lignin is a very complex heteropolymer that can only be degraded by white rot fungi. Degradation is complete without energy value to the fungus. The evolution of this ability has apparently given the organism the ability to degrade structurally diverse and normally very recalcitrant environmental pollutants such as DDT, PCB, benzo(a)pyrene, TNT, etc. Some of the major enzymes that are secreted by the fungi are peroxidases with unique properties. In addition to their ability to catalyze a wide variety of oxidations, they can also catalyze indirect oxidations and reductions. The fungi synthesize and secrete hydrogen peroxide to activate the peroxidases, veratryl alcohol to serve as a free radical intermediate for indirect oxidations, and electron donors, such as oxalate, which with veratryl alcohol catalyze reductions. Reductions are often required for subsequent oxidation of chemicals by the peroxidases. The enzymes can also reduce molecular oxygen.

Basidiomycota↗
PubMed1991

Effect of pretreatment on simultaneous saccharification and fermentation of hardwood into acetone/butanol.

The effectiveness of pretreatments on hardwood substrate was investigated in connection with its subsequent conversion by simultaneous saccharification and fermentation (SSF), using Clostridium acetobutylicum. The main objectives of the pretreatment were to achieve efficient separation of lignin from carbohydrates, and to obtain maximum sugar yield on enzymatic hydrolysis of pretreated wood. Two methods have given promising results: (1) supercritical CO2-SO2 treatment, and (2) monoethanolamine (MEA) treatment. The MEA pretreatment removed above 90% of hardwood lignin while retaining 83% of carbohydrates. With CO2-SO2 pretreatment, the degree of lignin separation was lower. Under the scheme of SSF, the pretreated hardwood was converted to acetone, butanol, and ethanol (ABE) via single stage processing by cellulase enzyme system and C. acetobutylicum cells. The product yield in the process was such that 15 g of ABE/100 g of dry aspen wood was produced. In the overall process of SSF, the enzymatic hydrolysis was found to be the rate-limiting step. The ability of C. acetobutylicum to metabolize various 6-carbon and 5-carbon sugars resulted in efficient utilization of all available sugars from hardwood.

Acetone↗
PubMed1991

Metabolism of cyanide by Phanerochaete chrysosporium.

The oxidation of veratryl alcohol (3,4-dimethoxybenzyl alcohol) by lignin peroxidase H2 (LiP H2) from the white rot fungus Phanerochaete chrysosporium was strongly inhibited by sodium cyanide. The I50 was estimated to be about 2-3 microM. In contrast, sodium cyanide binds to the native enzyme with an apparent sodium cyanide dissociation constant Kd of about 10 microM. Inhibition of the veratryl alcohol oxidase activity of LiP H2 by cyanide was reversible. Ligninolytic cultures of P. chrysosporium mineralized cyanide at a rate that was proportional to the concentration of cyanide to 2 mM. The N-tert-butyl-alpha-phenylnitrone-cyanyl radical adduct was observed by ESR spin trapping upon incubation of LiP H2 with H2O2 and sodium cyanide. The identity of the spin adduct was confirmed using 13C-labeled cyanide. Six-day-old cultures of the fungus were more tolerant to sodium cyanide toxicity than spores. Toxicity measurements were based on the effect of sodium cyanide on respiration of the fungus as determined by the metabolism of [14C]glucose to [14C]CO2. We propose that this tolerance of the mature fungus was due to its ability to mineralize cyanide and that this fungus might be effective in treating environmental pollution sites contaminated with cyanide.

Alcohol Oxidoreductases↗
PubMed1980

Factor VIII related antigen/coagulant activity ratio as a predictor of fetal growth retardation: a comparison with hormone and uric acid measurements.

Factor VIII related antigen (VIIIRAg), Factor VIII coagulant activity (VIIIC), plasma uric acid, total plasma oestriol, plasma human placental lactogen (hPL) and urine oestrogen/creatinine ratio were measured in a group of 21 patients clinically suspected of fetal growth retardation and compared with normal pregnancy. Of the hormone assays, hPL was better than either oestrial or oestrogen/creatinine ratio at distinguishing between normal and growth retarded pregnancies. Uric acid levels tended to be higher than normal in patients with fetal growth retardation, but the best means of distinguishing normal from growth retarded pregnancies proved to be the VIIIRAg/VIIIC ratio. This ratio was significantly elevated in fetal growth retardation compared with normal pregnancy, and the increase was evident as early as 30 weeks gestation. Using the VIIIRAg/VIIIC ratio test, the outcome of 17 of the 21 suspect pregnancies could be correctly predicted.

Antigens↗
PubMed1980

Enzyme-linked immunoassay for placental lactogen in human serum.

We describe an enzyme-linked immunoassay for measuring human placental lactogen (HPL) in serum. After suitable dilution, sera are pipetted into the wells of polyvinyl microtitre plates previously coated with anti-HPL. After incubation the sera are decanted, and replaced by a conjugate of horseradish peroxidase and anti-HPL. An amount of enzyme proportional to the concentration of HPL in the serum is bound to the wells via an antibody--HPL--antibody bridge. Peroxidase activity is measured by oxidation of o-phenylenediamine, the resulting color being related to the concentration of HPL. Results correlate well with those by radioimmunoassay (r = 0.96). Our between-assay coefficient of variation was 13%; no discernible effect of protein was observed. This 4-h assay can be used to monitor placental function in pregnancy.

Evaluation Studies as Topic↗