METAL-CATALYZED INACTIVATION OF BOVINE GLUCOSE-6-PHOSPHATE-DEHYDROGENASE - ROLE OF THIOLS

The role of thiols as oxidant scavengers during inactivation of bovine glucose-6-phosphate dehydrogenase by metal-catalyzed oxidation system s has been studied in vitro, Partial inactivation of the enzyme was ac hieved by the metal-catalyzed oxidation systems Fe(II)/H2O2/EDTA or Fe (II)/H2O2/ADP under specific conditions, When EDTA as chelator was pre sent in the oxidation system, both cysteine and N-acetylcysteine at lo w concentrations (0.1-1 mM) drastically enhanced inactivation, while c ysteinyl-glycine and glutathione did not, The thiol-mediated inactivat ion was inhibitable by superoxide dismutase, Depletion of enzyme activ ity by cysteine was paralleled by an increase of the carbonyl content, which indicates oxidative injury. However, when EDTA as chelator was replaced by the natural chelator ADP, all thiols studied acted as anti oxidants, It is therefore concluded that the nature of the chelator as a constituent of the metal-catalyzed oxidation systems determines whe ther the antioxidative function of some thiols is shifted to a prooxid ative function against glucose-6-phosphate dehydrogenase.