THIOSULFATE REDUCTASE FROM CHLAMYDOMONAS

Thiosulfate reductase (thiosulfate-thiol sulfurtransferase, (EC 2.8.1. 3) TSR) and rhodanese (thiosulfate-cyanide sulfurtransferase, (EC 2.8. 1.1) RDN) activities have been identified in crude extracts from the e ukaryotic green alga Chlamydomonas reinhardtii. These activities co-pu rified after several purification steps and no isoforms have been sepa rated. Kinetic studies indicate that dithiols (DTE) exert a competitiv e inhibition on rhodanese activity, the affinity for DTE being 28-fold higher than that for cyanide. These results support the idea that bot h activities are mediated by the same protein. The activities are not sensitive to thiol reagents, whereas they are inhibited by specific ar ginine-modifying reagents. The physiological role of this enzyme could be basically the assimilation of S-sulfane by the alga.