Oxidation of methanol by facultative and obligate methylotrophs.

1. The newly isolated methanol obligate Methylomonas sp. and the methanol facultative Pseudomonas sp. oxidize methanol at an unchanged rate over concentration range from 0.1 to 600 mM; the oxidation rate by the obligate methylotroph is 2.5 times higher (300 nmoles O2/min/mg dry wt.). Low-molecular alcohols, formaldehyde and formate serve as respiratory substrates for the intact cells of both methylotrophs. 2. Methanol dehydrogenase of both methylotrophs isolated should be classified as the phenazine methosulphate-dependent pteridine-type enzyme of double methanol-and formaldehyde-dehydrogenase function. This soluble enzyme is stimulated about 10-fold by NH+4, which results in enhancement of V max, and shows the same specificity and the same affinity toward methanol and formaldehyde (K m about 5 X 10(-5) M). Heat-inactivation of the 10-fold purified enzyme is associated with the release of a watersoluble pigment with maximum fluorescence at 420-430 nm. 3. NAD-deendent formate dehydrogenase was found to catalyse the third step of methanol oxidation in both methylotrophs.