Crotonyl Coenzyme A Reductase Activity of Bovine Mammary Fatty Acid Synthetase

Abstract

Abstract Lactating bovine mammary fatty acid synthetase, the enzyme complex that synthesizes fatty acids from a primer, malonyl-CoA, and TPNH, is shown to have a relatively high crotonyl-CoA reductase activity. Throughout purification to homogeneity the ratio of the reductase to the synthetase activities remains constant and the two activities emerge superimposed on gel filtration. Although the investigation showed that the reductase activity of the enzyme is an inherent property of the enzyme, the pH profiles and the rates of recovery of the two activities of the enzyme by preincubation were not the same. Synthetase gave a bell-shaped pH profile with an optimum at pH 6.8 while the reductase reaction showed maximum activity in the range of pH 7 to 8.5. The reductase activity was influenced by preincubation while the synthetase was not. The crotonyl-CoA reductase reaction requires TPNH as electron donor, but at a 20-fold higher concentration DPNH will substitute for TPNH with 50% Vmax. As a result of the presence of the reductase activity crotonyl-CoA substitutes as a primer in fatty acid synthesis as effectively as butyryl-CoA, a primer decidedly better than acetyl-CoA.