An Enzymic Analysis of NADPH Production and Consumption in Candida utilis

Abstract

C. utilis CBS 621 was grown in chemostat cultures at radiation rate [D] of D = 0.1 h-1 on glucose, xylose, gluconate, acetate or ethanol as the growth-limiting substrate with ammonia or nitrate as the N source and analyzed for NADPH-producing and NADPH-consuming enzyme activities. Nitrate and nitrite reductases were strictly NADPH-dependent. For all C sources, growth with nitrate resulted in elevated levels of HMP [hexose monophosphate] pathway enzymes. NADP+-linked isocitrate dehydrogenase did not vary significantly with the NADPH requirement for biosynthesis. Growth on ethanol strongly enhanced activity of NADP+-linked aldehyde dehydrogenase. Neither NADP+-linked malic enzyme nor transhydrogenase activities were detectable under any of the growth conditions. The absence of transhydrogenase was confirmed by the enzyme profiles of cells grown on mixtures of glucose and formate. The HMP pathway and possibly NADP+-linked isocitrate dehydrogenase are the major sources of NADPH in C. utilis.