Impact of endosulfan on lactate dehydrogenase from the freshwater catfish Clarias batrachus

The impact of a sublethal concentration of an organochlorine insecticide endosulfan on the activity, specific activity, electrophoretic patterns and kinetic properties of crude and purified lactate dehydrogenase (LDH) from the liver and the skeletal muscle of the freshwater catfish, Clarias batrachus, was evaluated. The endosulfan significantly reduced the activity and the specific activity of liver and muscle LDH but had no effect on total protein content. The inhibition of LDH produced by endosulfan was of mixed competitive noncompetitive (KiE < KiES) nature in both the tissues. The PAGE shows the presence of one predominant LDH-specific band in the liver as well as the skeletal muscle. The muscle LDH is more anodic than the liver LDH. There are no endosulfan-associated differences in the relative charges of the crude as well as purified LDH in the two tissues. The relative molecular mass of purified LDH in the liver and the skeletal muscle remains unaltered in response to treatment to endosulfan. The purified LDH, like crude LDH, from the liver and the skeletal muscle in endosulfan-treated fish also shows mixed competitive-noncompetitive (KiE < KiES) inhibition. The nature of inhibition in vivo and in vitro appears to be the same. Oxamate acts as a mixed competitive-noncompetitive inhibitor of purified LDH from the liver and the skeletal muscle of the control fish. The inhibition pattern of the Liver LDH remains unaltered, whereas it is modulated by endosulfan in the case of muscle LDH. These results demonstrate that endosulfan inhibits liver and muscle LDH through enzyme-endosulfan complexing. (C) 1997 Academic Press.