A novel quinoprotein methanol dehydrogenase containing an additional 32-kilodalton peptide purified from Acetobacter methanolicus: Identification of the peptide as a MoxJ product

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Abstract
Acetobacter methanolicus is a unique acetic acid bacterium which has a methanol oxidase respiratory chain in addition to an ethanol oxidase respiratory chain. In this study, two different forms of methanol dehydrogenase (type I and II MDHs) were purified from A. methanolicus grown on methanol. Type I MDH was more basic (pI of 8.0) and smaller (M(r) of 148K) than type II MDH (pI of 6.7 and M(r) of 177K). Type I MDH consisted of alpha and beta subunits of 62 and 10 kDa, which has the same alpha 2 beta 2 conformation as the enzymes purified so far. The type II MDH contained an additional peptide of 32 kDa, of which a single copy was estimated to bind to the alpha 2 beta 2-MDH judging from the whole molecular weight and the stoichiometry of each subunit determined in sodium dodecyl sulfate-high-performance gel filtration chromatography. Compared with type I MDH, type II MDH exhibited a lower enzyme activity, but the electron-transfer activity to cytochrome cL was much more resistant to the inhibition with NaCl or EDTA. The possibility could be excluded that type II MDH is an artificial complex of type I MDH with a 32-kDa peptide, since it was inducible with methanol and could be detected in the periplasm, as well as the other subunits. Furthermore, the N-terminal amino acid sequence of the 32-kDa peptide showed a high homology to that of the moxJ product deduced from the DNA sequence of Paracoccus denitrificans or Methylobacterium extorquens AM1.(ABSTRACT TRUNCATED AT 250 WORDS)

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