EFFECTS OF PH ON THE MAXIMAL RATES OF REACTIONS CATALYZED BY NAD-DEPENDENT HYDROGENASE FROM ALCALIGENES-EUTROPHUS

The effects of pH on the maximal rates of the hydrogenase and diaphora se reactions with various accepters catalyzed by NAD-dependent hydroge nase from Alcaligenes eutrophus H16 were studied, The data indicate th at at all pH values investigated, the electron transfer to the accepto r is the rate-limiting stage; hence, the reaction rate is essentially determined by the redox properties of the second substrate, The role o f the slow conformational changes associated with hydrogenase activati on is critical for the patterns of pH profiles of the catalytic activi ties of the enzyme.