Purification and properties of methanol dehydrogenase from Methylophaga marina

Purification of methanol dehydrogenase from Methylophaga marina, in order to avoid the instability observed in crude extracts, was achieved initially by a rapid procedure using mainly an aqueous two-phase partition system composed of polyethylene glycol 1000 (50%, v/v) and potassium phosphate (50%, w/v). The purified enzyme gave a single band of protein after SDS-polyacrylamide gel electrophoresis. Antiserum raised against purified methanol dehydrogenase was used to detect possible protein contaminants in the enzyme preparation. The enzyme is an NAD-independent dehydrogenase containing pyrrolquinoline quinone (PQQ) as a prosthetic group. It is made of two apparently identical subunits giving a total MW of 145,000 for the native enzyme. The isoelectric point is 6.4. In addition to methanol and formaldehyde, multicarbon primary alcohols and aldehydes as well as secondary alcohols can be used as substrates. Except for ammonium chloride, which is a necessary activator in vitro, no effector was found which could modify the rate of enzyme activity under standard conditions of the assay. Although the main properties of this methanol dehydrogenase are similar to those already described in the literature, it does not belong in any of the five categories described by Anthony.