Substrate specificity of the purified primary alcohol dehydrogenases from methanol-oxidizing bacteria

Hyphomicrobium strain WC, Pseudomonas strain TP-1, and Pseudomonas strain W1 are capable of growth on methanol as the sole source of carbon and energy. Methanol-grown cells of each organism contain a primary alcohol dehydrogenase that has been purified to homogeneity. Each enzyme has a molecular weight of 120,000 and shows an in vitro requirement for phenazine methosulfate and ammonium ions for enzymatic activity. Normal aliphatic alcohols are oxidized rapidly by each enzyme. The presence of a methyl group on the carbon atom adjacent to the primary alcohol group lowers the enzymatic activity. This effect is reduced as the methyl substituent is moved further away from the hydroxyl group. The effect of other substituents on enzymatic activity is reported. Methanol, formaldehyde, and to a limited extent acetaldehyde are oxidized by the primary alcohol dehydrogenases. Higher aldehydes are not oxidized. A possible explanation for this specificity, with regard to aldehydes, is presented in terms of degree of hydration of the aldehyde.