A Radiorespirometric Study on the Contribution of the Hexose Monophosphate Pathway to Glucose Metabolism in Candida utilis CBS 621 Grown in Glucose-limited Chemostat Cultures

摘要

Summary: A radiorespirometric study of glucose metabolism in Candida utilis CBS 621 was done using glucose-limited chemostat cultures growing at a dilution rate of 0.1 h?1 with ammonium or nitrate as the nitrogen source. From a steady-state analysis of 14CO2 yields from [1-14C]- and [6-14C]glucose supplied in the medium feed it appeared that during growth with nitrate the flow of glucose through the hexose monophosphate (HMP) pathway was much higher than during growth with ammonium as the nitrogen source. The same phenomenon was apparent from an analysis of the rate of 14CO2 production after administration of small amounts of labelled glucose to samples withdrawn from steady-state cultures. Additionally, these experiments revealed not only that the initial fraction of glucose 6-phosphate routed into the HMP pathway increases, but also that recycling of hexose phosphates via this pathway increases when nitrate is used as the nitrogen source. From a quantitative analysis of the results it is concluded that the contribution of the HMP pathway to glucose metabolism is close to the theoretical minimum required to cover the NADPH requirement for biosynthesis.