title: Kinetics of succinic dehydrogenase inhibition by methyl parathion and its recovery by oximes and L-cysteine in hepatopancreas of Lamellidens marginalis.
abstract: Effects in vitro of methyl parathion on some kinetic constants of succinic dehydrogenase (SDH) in hepatopancreas of freshwater mussel, L. marginalis were studied. Altered pH vs. specific activity curves for SDH demonstrated significant inhibition by methyl parathion in buffered acidic, neutral and alkaline ranges. At high pH ranges IC50 (12.5 microM) of methyl parathion did not cause 50% inhibition enzyme as it did at neutral and acidic pHs. Activation energies (delta E) were found to be increased suggesting decreased efficiency of enzyme in presence of methyl parathion. Non-competitive inhibition with respect to activation by succinate was indicated by decreased maximal velocity (V) without change in Michaelis Menten constant (Km). Pyridine-2-aldoxime (25 microM), pyridine-4-aldoxime (15 microM) and L-cysteine (40 microM) neutralized the inhibition of SDH by methyl parathion (12.5 microM). The kinetic data suggests that inhibition of SDH by methyl parathion was pH and temperature independent.
mesh_terms: D000818:Animals; D049872:Bivalvia / Q000201:enzymology*; D003545:Cysteine / Q000494:pharmacology; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D008099:Liver / Q000201:enzymology; D008743:Methyl Parathion / Q000494:pharmacology*; D010091:Oximes / Q000494:pharmacology; D010179:Pancreas / Q000201:enzymology; D010278:Parathion / Q000031:analogs & derivatives*; D013385:Succinate Dehydrogenase / Q000037:antagonists & inhibitors*; D013696:Temperature
chemical_list: D010091:Oximes; D008743:Methyl Parathion; D010278:Parathion; D013385:Succinate Dehydrogenase; D003545:Cysteine