Formation of d-3-hydroxybutyryl-coenzyme A by an acetoacetyl-coenzyme A reductase in Syntrophomonas wolfei subsp. wolfei

Cell-free extracts of Syntrophomonas wolfei subsp. wolfei synthesized d-(-)-3-hydroxybutyryl-coenzyme A (CoA) (the stereoisomer required for the synthesis of poly--hydroxyalkanoate) from acetoacetyl-CoA, but not crotonyl-CoA, and NAD(P)H. Ammonium sulfate fractionation and ion exchange chromatography separated an acetoacetyl-CoA reductase activity that formed d-(-)-3-hydroxybutyryl-CoA from the -oxidation enzyme activity, l-(+)-3-hydroxyacyl-CoA dehydrogenase. The former activity was further purified by hydroxylapatite and affinity chromatography. The most pure acetoacetyl-CoA reductase preparations formed d-(-)-3-hydroxybutyryl-CoA from acetoacetyl-CoA and had high specific activities using either NADH or NADPH as the electron donor. Thus, S. wolfei makes d-(-)-3-hydroxybutyryl-CoA by an acetoacetyl-CoA reductase rather than by a d-isomer specific enoyl-CoA hydratase and the reducing equivalents required for PHA synthesis from acetoacetyl-CoA can be supplied from the NADH made during -oxidation.