[Regulation of glucose-6-phosphate dehydrogenase in the obligate methylotrophic bacterium Pseudomonas W6]

[Regulation of PEP-carboxylase of the facultative methylotrop Acetobacter sp. MB 58]

Acetobacter sp. MB 58 assimilates methanol via the fructose-1,6-bisphosphate variant of the hexulose phosphate pathway. Glyceraldehyde-3-phosphate originates as net product of an assimilation loop involving the regeneration of the C1-acceptor ribulose-5-phosphate and must be available for the de novo synthesis of the C1-acceptor as well as for the oxidative glycolysis. It is made probable in a regulatory model that this is accomplished via alternating anabolic and catabolic phases which are controlled by concerted action of PEP-carboxylase and pyruvate kinase. Whereas Ac-CoA is a crucial effector and alpha-ketoglutarate and aspartate are inhibitors for the PEP-carboxylase, the pyruvate kinase is assumed to be regulated by energy charge.

Purification and properties of glucose-6-phosphate dehydrogenase (NADP+/NAD+) and 6-phosphogluconate dehydrogenase (NADP+/NAD+) from methanol-grown Pseudomonas C

Glucose-6-phosphate dehydrogenase (D-glucose-6-phosphate:NADPH+ 1-oxidoreductase, EC 1.1.1.49) and 6-phosphogluconate dehydrogenase (6-phospho-D-gluconate:NADP+ 2-oxidoreductase, EC 1.1.1943) have been purified from methanol-grown Pseudomonas C. Glucose-6-phosphate dehydrogenase exhibits activity with either NADP+ or NAD+ as coenzymes, V NADP+ = 0.96 V NAD+.Km values of 22, 290, and 250 microns are obtained for NADP+, NAD+ and glucose 6-phosphate (NADP+ as the coenzyme), respectively. ATP inhibits Glc-6P dehydrogenase activity with NAD+ as coenzyme and to a less extent the activity with DANP+. In the presence of MgCl2, ATP inhibition of Blc-6P dehydrogeanse activity is abolished. 6-Phosphogluconate dehydrogenase has a dual specificity for both NADP+ or NAD+ as coenzymes, V NADP+ = 1.66 V NAD+.Km values of 20, 500 and 100 microns are obtained for NADP+, NAD+ and 6-phosphogluconate (NADP+ as the coenzyme), respectively. With NAD+ as the coenzyme ATP inhibits 6-phosphogluconate dehydrogeanse activity, while with NADP+ as the coenzyme, activity was less affected. The possible role of these enzymes in the metabolism of one-carbon (C1)-compounds in Pseudomonas C is discussed and compared with other methylotrophic microorganisms.