Ribulose bisphosphate carboxylase is present at a high specific activity in extracts of methanol-grown Microccus denitrificans. Enzymic and physiological evidence indicates that, during growth on methanol, the ribulose bisphosphate cycle is the route of carbon assimilation.

SUMMARYRhodopseudomonas acidophila strain I 0050, grown anaerobically in the light on methanol, contained a methanol and formaldehyde dehydrogenase which could be coupled to phenazine methosulphate ; an NAD-linked formaldehyde dehydrogenase which required GSH for activity; and an NAD-linked formate dehydrogenase. The specific activities of these enzymes varied in a non-coordinate manner when the organism was grown on different alcohols, formate or succinate. The affinity of the phenazine methosulphate linked methanol dehydrogenase for methanol was increased 10-fold if the cell-free extract was prepared and assayed in the absence of oxygen. Pulse-labelling experiments with [14C]methanol and [14C]bicarbonate indicated that fixation of carbon dioxide occurred via the ribulose diphosphate cycle and C3 + COz fixation reaction(s). No evidence was obtained for operation of a reduced C, fixation sequence. This conclusion was borne out by the enzyme content of cell-free extracts of the organism.

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