Abstract
Cyanocobinamide (Factor B) and aquocobalamin (OH-B_<12>) inhibited yeast alcohol dehydrogenase (YADH). This inhibition was remarkably increased by the addition of GSH. GSSG, however, did not affect the inhibition of YADH with OH-B_<12> or Factor B. The inhibition with Factor B and GSH was suppressed by the addition of catalase. Completely inhibited YADH, obtained by the gel filtration of a reaction mixture, was found to lose about 7 SH groups (mol/YADH mol) and to release the GSH bound to the enzyme by CySH reduction. The inhibited YADH was partially reactivated by CySH. From these results it was concluded that OH-B_<12> and Factor B catalyze the formation of mixed disulfides between small molecular thiols and YADH.
