Abstract
NADPH-dependent acetoacetyl-CoA (AcAc-CoA) reductase (EC 1.1.1.36) was purified to electrophoretic homogeneity from the methylotroph Methylobacterium extorquens – a producer of poly-3-hydroxybutyrate. The enzyme has an M r of 141 000 and consists of four identical subunits ( M r 31 000) and demonstrates absolute specificity for NADPH as cofactor. NADPH-AcAc-CoA reductase is inhibited by NADPH, AcAc-CoA, NADP and NAD but is activated by isocitrate and ATP. The calculated K m values were 11.6 and 41 μM for AcAc-CoA and NADPH, respectively. The results suggest that this enzyme plays a more important role in the coordinated operation of the tricarboxylic acid cycle and poly-3-hydroxybutyrate synthesis in M. extorquens than in the taxonomically related M. rhodesianum MB 126.
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