The radiolysis of glyceraldehyde-3-phosphate dehydrogenase.

Abstract

This study quantified the radiation-induced loss of active sites and sulphydryl groups from glyceraldehyde-3-phosphate dehydrogenase, expressed as molecules per 100 eV, across nitrous-oxide-saturated, aerated, and argon-saturated aqueous solutions. Molecular hydrogen peroxide generated a sulphenic acid derivative that could be restored by post-irradiation dithiothreitol treatment. Under aerated conditions, both hydroxyl radicals (.OH) and superoxide radicals (.O2-) inactivated the enzyme at approximately 26% efficiency. In oxygen-free solutions, .OH efficiency was reduced, and inactivation attributable to hydrogen radicals (.H) or hydrated electrons (eaq-) was not substantial. A clear correlation was observed between sulphydryl group loss and active-site inactivation, suggesting that SH oxidation is a primary mechanism of enzyme damage.

Mechanism

Hydroxyl and superoxide radicals generated by radiolysis oxidize sulphydryl groups at or near the enzyme active site, forming sulphenic acid intermediates and causing loss of catalytic activity.