Pyruvate and phosphoenolpyruvate carboxylase in methylotrophs

The activity of pyruvate and phosphoenolpyruvate carboxylases was determined in cell extracts of obligate and facultative methylotrophs which metabolized monocarbon reduced compounds via different pathways. Phosphoenolpyruvate carboxylase was found to be the only enzyme responsible for the high level of CO2 fixation by methylotrophs with the serine pathway (Methylosinus trichosporium, Hyphomicrobium vulgare, Pseudomonas methylica). Methylotrophs with the hexulose phosphate pathway Mehylobacter chroococcum, Methylomonas methanica, Pseudomonas oleovorans, Arthrobacter globiformis) and yeast (Candida methylica) assimilated less CO2 but contained more enzymes involved in arboxylation of phosphoenolpyruvate (phosphoenolpyruvate carboxylase, EG 4.1.1.31; phosphoenolpyruvate carboxykinase, EC 4.1.1.32) or pyruvate (pyruvate carboxylase, EC 6.4.1.1; malic-enzyme, EC 4.1.1.40). Phosphoenolpyruvate carboxytransphosphorylase (EC 4.1.1.38) was not found in any of the studied strains. The properties and the role of carboxylases in the metabolism of methylotrophs are discussed.