POSSIBLE DIFFERENCES IN THE REGENERATIVE ROLES PLAYED BY THIOLTRANSFERASE AND THIOREDOXIN FOR OXIDATIVELY DAMAGED PROTEINS

A possible involvement of thioltransferase (also known as glutaredoxin ) in the regenerative reaction of proteins inactivated by oxidative st ress were examined in vitro using the enzyme purified from bovine live r. Thioltransferase at physiological concentrations, together with glu tathione, glutathione reductase and NADPH, regenerated the oxidatively damaged proteins with a comparable potency to that of thioredoxin. Ex periments performed with protein substrates with their critical cystei ne residues oxidized differently, that is, phosphofruktokinase and gly ceraldehyde 3-phosphate dehydrogenase with mixed disulfide bonds and g lyceraldehyde 3-phosphate dehydrogenase with sulfenyl or sulfinyl grou ps, indicated that thioltransferase regenerated the proteins inactivat ed by mixed disulfide formation more efficiently than thioredoxin, whe reas thioredoxin preferentially regenerated the proteins inactivated b y monothiol oxidation to sulfenic or sulfinic acid. These findings sug gested that thioltransferase exerted regenerative effects on oxidative ly damaged proteins like its cognate protein, thioredoxin, but with di fferent substrate specificity, and their relative contribution to the regeneration reaction is dependent on the form of the oxidized thiols of the damaged proteins.