The obligate methanol-utilising bacterium strain 4025 contains cytochromes b and c. Cytochrome a is never present. 2. The soluble cytochrome c is similar to that from other methylotrophs in reacting (slowly) with carbon monoxide and it can be separated into two types, differing markedly in their isoelectric points. 3. Some of the cytochrome b reacts rapidly with carbon monoxide and is thus the likely cytochrome oxidase (cytochrome o). 4. The partially purified, NAD+-independent methanol dehydrogenase is similar to such enzymes from the other methanol-utilising bacteria in respect of its prosthetic group, dependence on ammonia or methylamine for activity and its wide substrate specificity. 5. The fluorescence seen in colonies of this organism is probably due to a flavin derivative. 6. This study of electron transport components does not shed any light on the unusually high copper requirement shown by this methylotroph.
