Sreenivasa Moorthy K, Kasi Reddy B, Swami K S, Sreeramulu Chetty C
Arch Int Physiol Biochim. 1984 Oct;92(3):147-51. doi: 10.3109/13813458409104494.
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.
研究了甲基对硫磷对淡水贻贝边缘鳞虫肝胰腺中琥珀酸脱氢酶（SDH）某些动力学常数的体外影响。SDH的pH与比活性曲线的改变表明，在缓冲的酸性、中性和碱性范围内，甲基对硫磷具有显著抑制作用。在高pH范围内，甲基对硫磷的IC50（12.5微摩尔）不像在中性和酸性pH时那样能使酶产生50%的抑制。发现活化能（ΔE）增加，这表明在甲基对硫磷存在下酶的效率降低。琥珀酸激活的最大速度（V）降低，而米氏常数（Km）不变，表明对琥珀酸激活存在非竞争性抑制。吡啶 - 2 - 醛肟（25微摩尔）、吡啶 - 4 - 醛肟（15微摩尔）和L - 半胱氨酸（40微摩尔）可中和甲基对硫磷（12.5微摩尔）对SDH的抑制。动力学数据表明，甲基对硫磷对SDH的抑制与pH和温度无关。
