The influence of malathion and its decomposition products on free and immobilized acetylcholinesterase

The influence of malathion and its four main degradation products found in irradiated solutions (malaoxon, isomalathion, diethyl maleate and O,O-dimethyl phosphate) on acetylcholinesterase (AChE) of free and immobilized bovine erythrocytes was investigated. The concentration-dependent responses to malathion and related organophosphates, malaoxon and isomalathion, of both AChE bioassays used were obtained. The IC (50) values for free and immobilized AChE (3.7 +/- 0.2) x 10(-4) M/(1.6 +/- 0.1) x 10(-4), (2.4 +/- 0.3) x 10(-6)/(3.4 +/- 0.1) x 10(-6) M, and (3.2 +/- 0.3) x 10(-6) M/(2.7 +/- 0.2) x 10(-6) M were obtained in the presence of malathion, malaoxon and isomalathion, respectively. However, diethyl maleate inhibited AChE activity at concentrations GT = 10 mM, while O,O-dimethyl phosphate did not noticeably affect enzyme activity at all investigated concentrations. The relation between the structure of the compounds and their ability to inhibit enzyme activity was discussed