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.
Subject(s)
Bivalvia/enzymology , Methyl Parathion/pharmacology , Parathion/analogs & derivatives , Succinate Dehydrogenase/antagonists & inhibitors , Animals , Cysteine/pharmacology , Hydrogen-Ion Concentration , Kinetics , Liver/enzymology , Oximes/pharmacology , Pancreas/enzymology , TemperatureABSTRACT
Oxygen consumption and sodium, potassium and calcium concentration were determined in the freshwater mussel, Lamellidens marginalis, and its tissues during methyl parathion (MP) toxicity. A transient increase followed by decrease in whole animal or tissue respiration as a function of time was observed. Greater loss of calcium by the mantle, sodium by the gill, and calcium and sodium by the hepatopancreas and foot was observed. As compared to calcium and sodium, the loss of potassium by the tissues was less.
