METHYLOBACTERIUM RHODESIANUM MB-126 POSSESSES 2 ACETOACETYL-COA REDUCTASES

Two constitutive acetoacetyl-CoA (AcAc-CoA) reductases were purified from Methylobacterium rhodesianum MB 126, an NADPH-linked D(-)-beta-hydroxybutyryl-CoA forming reductase (enzyme A) and an NADH- and NADPH-linked L(+)-beta-hydroxybutyryl-CoA forming reductase (enzyme B.) Enzyme A and B give apparent K-m values of 15 mu M and 30 mu M for AcAc-CoA, 18 mu M for NADPH and 30 mu M for NADH, respectively. They are inhibited by AcAc-CoA at concentrations higher than 25 mu M and 50 mu M, respectively. The contribution of the two reductases to poly-beta-hydroxybutyrate synthesis is discussed.