The role of NADH- and NADPH-linked acetoacetyl-CoA reductases in the poly-3-hydroxybutyrate synthesizing organism<i>Alcaligenes eutrophus</i>

Abstract

Two constitutive acetoacetyl-CoA (AcAc-CoA) reductases were purified from Alcaligenes eutrophus.Incorporation of [1)4C]-acetyl-CoA into poly-3-hydroxybutyrate (PHB) by systems reconstituted from purified preparations of either 3-ketothiolase, AcAc-CoA reductase and PHB synthase, occurred only when NADPH-AcAc-CoA reductase was present.The NADH reductase was active with all of the D(-)-and L( + )-3-hydroxyacyl-CoA substrates tested (C4-Ct0), whereas the NADPH reductase was only active with D(--)-3hydroxyacyl-CoAs (C4-C6).The products of AcAc-CoA reduction by the NADH-and NADPH-linked enzymes were L(+)-3-hydroxybutyryl-CoA and D(-)-3-hydroxybutyryl-CoA, respectively.The NADH-linked enzyme had an M r of 150,000 (containing identical M r 30,000 subunits) and the NADPH-linked enzyme appeared to be a tetramer (M, 84,000) with identical sub-