METHYLOBACTERIUM-RHODESIANUM MB-126 POSSESSES 2 STEREOSPECIFIC CROTONYL-COA HYDRATASES

Two distinct crotonyl-CoA hydratases of Methylobacterium rhodesianum MB 126 were separated by column chromatography on DEAE-Sepharose CL-6B. The two enzymes were further purified by chromatography on red 120 agarose and Mono Q. Enzyme A was specific for L(+)-hydroxybutyryl-CoA. It had an apparent molecular weight of 160 000 with two identical subunits of 43 000 and 34 000. The apparent K-m values for L(+)-hydroxybutyryl-CoA and crotonyl-CoA were 83 and 90 mu M, respectively. Enzyme B was specific for D(-)-hydroxybutyryl-CoA. It had an apparent molecular weight of 39 000 with identical subunits of 12 500. It showed sigmoidal kinetics for crotonyl-CoA, and the Hill coefficient was about 2.5. The apparent K-m value for D(-)-hydroxybutyryl-CoA was 0.5 mM. The possible contribution of a sequence including beta-ketothiolase, NADH-linked L(+)-specific acetoacetyl-CoA reductase, and two stereospecific crotonyl-CoA hydratases to PHB synthesis in methylotrophic serine-pathway bacteria is discussed.