An NADH-Dependent Acetoacetyl-CoA Reductase from Euglena gracilis: Purification and Characterization, Including Inhibition by Acyl Carrier Protein

An NADH-dependent acetoacetyl-CoA reductase from Euglena gracilis variety bacillaris was extensively purified and characterized. Two different isoelectric forms of the reductase with identical characteristics otherwise were found. The reductase was noncompetitively inhibited by acyl carrier protein, K_i 5.6 micromolar at pH 5.4; this inhibition decreased with increasing pH or ionic strength. Coenzyme A was a competitive inhibitor, K_i 230 micromolar. Kinetic parameters with respect to acetoacetyl-CoA and NADH were sensitive to changes in pH and ionic strength.