Nicotinoprotein methanol dehydrogenase enzymes in Gram-positive methylotrophic bacteria

A novel type of alcohol dehydrogenase enzyme has been characterized from Gr am-positive methylotrophic (Bacillus methanolicus, the actinomycetes Amycol atopsis methanolica and Mycobacterium gastri) and non-methylotrophic bacter ia (Rhodococcus strains). Its in vivo role is in oxidation of methanol and other primary alcohols. B. methanolicus displays activity of an NAD-depende nt methanol dehydrogenase (MDH), which is strongly stimulated by a specific (activator) protein. A. methanolica and M. gastri use an N,N'- dimethyl-4- nitrosoaniline (NDMA)-dependent MDH (methanol: NDMA oxidoreductase; MNO). M DH (43 kDa subunit) and MNO (49 kDa subunit) possess similar decameric stru ctures with five-fold symmetry, Both proteins contain Zn2+- and Mg2+-ions a nd tightly (but non-covalently) bound NAD(P)(H) cofactors. These nicotinopr oteins share a high degree of sequence similarity; they belong to Family II I of NAD(P)-dependent alcohol dehydrogenases (ADH). A. methanolica extracts also possess dye (dichlorophenol indophenol, DCPIP and 3-[4,5-dimethylthia zol-2-yl]-2,5-diphenyl-tetrazolium bromide, MTT)-linked ADH activities. The se represent the overall activities of multi-enzyme systems. MNO is part of the MTT-ADH complex. The other two proteins and their cofactors most likel y participate in transfer of reducing equivalents from the NADPH cofactor i n MNO to the respiratory chain. (C) 2000 Elsevier Science B.V. All rights r eserved.