Rhodanese as a thioredoxin oxidase

A major catalytic difference bt tween thr two most common isoforms of bovin e liver mitochondrial rhodanese (thiosulfate: cyanide sulfurtransferase, EC 2.8.1.1) has bren observed. Both isoforms were shown to be capable of usin g reduced thioredoxin as a sulfur-acceptor substrate. However, only the les s negative form in common with the recombinant mammalian rhodanese expresse d in E, coli. can also catalyze the direct oxidation of reduced thioredoxin evidently by reactive oxygen species. These activities are understood in t erms of the established persulfide structure (R-S-SH) of the covalently sub stituted rhodanese in the sulfurtransferase reaction and an analogous sulfe nic acid structure (R-S-OH) when the enzyme acts as a thioredoxin oxidase. The observations suggest a role for one rhodanese isoform in the detoxicati on of intramitochondrial oxygen free radicals. (C) 2000 Published by Elsevi er Science Ltd, All rights reserved.