Characterization of the Assimilatory and Dissimilatory Pathways of Carbon Metabolism during Growth of Methylophilus methylotrophus on Methanol

Abstract

The enzyme profile of methanol-grown Methylophilus methylotrophus has been determined. It shows that the organism uses a variant of the ribulose monophosphate cycle of formaldehyde fixation that involves cleavage of hexose phosphate by 2-keto-3-deoxy-6-phosphogluconate aldolase and a rearrangement sequence involving transketolase and transaldolase. The organism possesses high concentrations of a glucose-6-phosphate dehydrogenase active with both NADP+ and NAD+, and two separate 6-phosphogluconate dehydrogenases, one active with both NADP and NAD+ and the other active only with NAD+. In addition, the organism contains methanol dehydrogenase, and NAD+-linked formaldehyde and formate dehydrogenases, thus possessing the enzymic potential necessary for both cyclic and linear sequences for oxidation of the formaldehyde derived from methanol. Hexulose phosphate synthase, phosphohexuloisomerase, glucose-6-phosphate dehydrogenase and the two 6-phosphogluconate dehydrogenases have been purified, characterized and examined for possible regulatory properties.