2,4-dienoyl-CoA reductase from Escherichia coli is a novel iron-sulfur flavoprotein that functions in fatty acid beta-oxidation

2,4-Dienoyl-CoA reductase is an enzyme that is required for the beta-oxidat ion of unsaturated fatty acids with even-numbered double bonds, The 2,4-die noyl-CoA reductase from Escherichia coli was studied to explore the catalyt ic and structural properties that distinguish this enzyme from the correspo nding eukaryotic reductases. The E. coli reductase was found to contain 1 m ol of flavin mononucleotide and 4 mol each of acid-labile iron and sulfur i n addition to 1 mol of flavin adenine dinucleotide per mole of protein. Red ox titrations revealed a requirement for 5 mol of electrons to completely r educe 1 mol of enzyme and provided evidence for the formation of a red semi quinone intermediate. The reductase caused a significant polarization of th e substrate carbonyl group as indicated by an enzyme-induced red shift of 3 8 nm in the spectrum of 5-phenyl-2,4-pentadienoyl-CoA. However, suspected c is --> trans isomerase and Delta(3),Delta(2)-enoyl-CoA isomerase activities were not detected in this enzyme. It is concluded that the 2,4-dienoyl-CoA reductases from E. coli and eukaryotic organisms are structurally and mech anistically unrelated enzymes that catalyze the same type of reaction with similar efficiencies. (C) 2000 Academic Press.