Characterisation of a red form of methanol dehydrogenase from the marine methylotrophMethylophaga marina

The quinoprotein methanol dehydrogenase (MDH) of the marine methylotroph Methylophaga marina is similar to that of other methylotrophs in being an α2β2 tetramer containing two molecules of PQQ and a single atom of calcium. Its electron acceptor is cytochrome cL and interaction of the two proteins is by way of carboxylates on the cytochrome and lysyl residues on the α subunit of MDH. The reaction was not, however, sensitive to high ionic strength as was the reaction in non-halophilic bacteria. A red form of the enzyme was sometimes produced which had a low specific activity and a low calcium content. Activity was restored by incubation with Ca2+ which also produced the typical (green) enzyme, with a typical absorption spectrum. This provides the first demonstration of reconstitution of active MDH from enzyme lacking calcium isolated from a wild-type methylotroph.