Oxidation, photosensitized by certain diketones, of enzymes and protection against such oxidation by histidine derivatives

Abstract

Bovine milk lactoperoxidase, eel acetylcholinesterase, and Aeromonas aminopeptidase were photooxidized and inactivated in broad-spectrum visible light in the presence of 2,3-butanedione and l-phenyl-l,2-propanedione. Methylglyoxal caused similar effects at 25zt nm. 2-Thiol-L-histidine and 3-methyl-L-histidine protected the enzymes against photoinactivation more effectively than N3−, even at a molar ratio of 2:1 (protector to enzyme). These compounds also delayed the photoinactivation of acetylcholinesterase, induced by ultraviolet light.