Purification and characterization of cytoplasmic thioltransferase (glutathione:disulfide oxidoreductase) from rat liver

Abstract

An enzyme catalyzing thiol-disulfide interchange of glutathione and disulfides and the reaction between glutathione and thiosulfate esters was purified 40,000-fold from rat liver cytosol. The enzyme, named thioltransferase was homogeneous in several electrophoretic systems, had an isoelectric point at pH 9.6, and contained 8.6% (wt/wt) carbohydrate. The catalytic activity had a distinct optimum at pH 7.5. A series of substrates was tested at a constant glutathione level; the kcat values (at 4 mM glutathione) were all in the range of about 104 min-1. The substrates included mixed disulfides of glutathione, other low MW disulfides, S-sulfocysteine and S-sulfoglutathione and peptide disulfides such as insulin, oxytocin, RNAse and the mixed disulfide glutathione and egg-white lysozyme. The enzymatic reaction was inhibited by an excess of glutathione (> 4 mM).