Metabolism of methanol by Rhodopseudomonas acidophila

Rhodopseudomonas acidophila strain 10050, 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 [14C5methanol and [14C]bicarbonate indicated that fixation of carbon dioxide occurred via the ribulose diphosphate cycle and C3 + CO 2 fixation reaction(s). No evidence was obtained for operation of a reduced C1 fixation sequence. This conclusion was borne out by the enzyme content of cell-free extracts of the organism.