Comparative analysis of two types of methanol dehydrogenase from Methylophaga aminisulfidivorans MPT grown on methanol

Two types of methanol dehydrogenase (MDH) were obtained from a novel marine methylotrophic bacterium, Methylophaga aminisulfidivorans MPT, grown on methanol. Type I MDH consisted of two identical dimers of α (65.98 kDa) and β (7.58 kDa) subunits organized to form the α2β2tetramer. Type II MDH contained an additional MxaJ protein (27.86 kDa) and had more specific activity than type I MDH. The Km values of type I and II MDH for methanol under cytochrome cL reduction assay system were estimated to be 50.3 and 13.0 μM, respectively, and the isoelectric points of type I and II MDH were determined to be 5.4 and 5.8, respectively. The average molar ratios of α:β, α:MxaJ, and β:MxaJ in type II MDH were approximately 1:0.99, 1:0.41 and 1:0.42, respectively. Based on these results, the original conformation of the MDH of M. aminisulfidivorans MPTis most likely the α2β2-MxaJ complex. During purification, the lysozyme and freeze-thawing cell disruption method significantly increased the amount of type II MDH in the soluble fraction compared with strong physical disruption methods such as sonication and French Press. (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)