HYDROGENASE-I OF CLOSTRIDIUM-PASTEURIANUM FUNCTIONS AS A NOVEL SELENITE REDUCTASE

Clostridium pasteurianum's hydrogenase I, an important constitutive me tabolic enzyme, has been shown to function as a 'novel selenite reduct ase: Selenite reductase activity was found to co-purify with hydrogena se I activity; the fold purification and specific activities for these two activities paralleled each other throughout the purification step s. The highly purified hydrogenase I apparent K-m for the selenite sub strate was 0.2 mM. The stoichiometry for the enzymatic reduction of Se O32- to Se-0 via H-2 oxidation, was determined to be 2.3:1(H-2:Se-0), very close to the theoretical ratio of 2:1 for this reduction reaction . Known electron carriers required for hydrogenase I activity were als o found to couple its selenite reductase activity, the most efficient one being ferredoxin. The purified hydrogenase I not only reduced sele nite but also tellurite, and its selenite activity was completely inhi bited by O-2 and CuSO4, potent inhibitors of hydrogenase I activity.