Analogous Mechanisms of Biological Damage Induced by Ascorbate and Superoxide in the Presence of Copper. Progress Report, July 1982-June 1983

摘要

The mechanism of enzymatic inactivation of purified and membrane-bound acetylcholine esterase (AChE) by ascorbate and copper was investigated. While the exposure of the enzyme to either ascorbate or copper did not cause enzymatic inactivation, the incubation of the enzyme with a combination of both ascorbate and copper resulted in a loss of AChE activity, which was time dependent. The presence of molecular oxygen or hydrogen peroxide was indispensable for the enzymatic inactivation. Scavengers of hydroxyl radicals at concentrations of up to 100mM did not provide protection to AChE. Only mannitol at very high concentrations (above 1M) efficiently prevented the inactivation of the enzyme. The kinetics of the aerobic oxidation of reduced ascorbate in the presence of AChE and copper closely followed the rate of enzyme inactivation. Addition of the chelating agents, EDTA and diethylentriaminepentaacetic acid, prevented both the oxidation of ascorbate and the inactivation of the enzyme. In the presence of low concentrations of histidine (0.5 to 2.0mM), which forms high affinity complexes with copper, the rate of ascorbate oxidation was similar to that recorded in its absence. On the other hand, no enzyme inactivation was indicated in the presence of histidine. Low temperature EPR measurements have demonstrated the binding of copper to the enzyme, and have shown the reduction of the cupric-enzyme to the corresponding cuprous complex. (ERA citation 08:044758)