Purification and steady-state kinetic analysis of yeast thiosulfate reductase.

Thiosulfate reductase has been purified approximately 70-fold from an extract of bakers' yeast. An enzyme with a molecular weight of 17,000, a Stokes radius of 19 Å, and a pI of 5.1 was obtained. Initial velocity and inhibition studies indicate that the substrates add in a random fashion. Further evidence suggests that the rapid-equilibrium assumption is not totally applicable. The enzyme has two distinct but closely situated substrate binding sites—one for compounds with an RSO₃^? structure and one for the sulfhydryl substrate.