Purification and properties of methanol dehydrogenase from Hyphomicrobium x

(1) A method for the isolation of methanol dehydrogenase (alcohol:(acceptor) oxidoreductase, EC 1.1.99.8) from Hyphomicrobium X is decribed. The purified enzyme was resolved by polyacrylamide gel electrophoresis into one main and two minor active bands. Iron and manganese were the only detected metals in the enzyme preparation. (2) The substrate, methanol, was oxidized to formic acid by a stoichiometric amount of artificial electron acceptor. During the reaction, no free formaldehyde could be detected. Other primary alcohols were oxidized to the corresponding aldehydes were a poor substrate or no substrate at all. (3) Some new and efficient one-electron acceptors were found. With these electron acceptors, the enzyme had a high pH optimum and ammonia was still required in the assay system. (4) ESR spectroscopy showed the presence of an enzyme-bound organic free radical. With X-band ESR the signal had a peak-to-peak linewidth of about 0.7 mT. The signal was further resolved by Q-band ESR and the values gparallel = 2.0024 and gperpendicular = 2.0056 were derived. (5) Under denaturing conditions the ESR signal and enzymatic activity disappeared at the same time as fluorescence appeared. Enzymatic activity is not restored when extracted cofactor and apoenzyme are brought together under normal conditions. Some properties of the unusual prosthetic group are presented in a preliminary form.