The purification and properties of the fatty acid synthetase of pigeon liver.

The fatty acid synthetase of pigeon liver catalyzes the conversion of acetyland malonyl-coenzyme A to long chain saturated fatty acids in the presence of reduced nicotinamide adenine dinucleotide phosphate. The major product of the reaction is palmitic acid, but small amounts of other long chain fatty acids are also formed. The over-all reaction for the synthesis of palmitic acid is: 1 acetyl-CoA + 7 malonyl-CoA + 14 NADPH + 14 H+ + 1 palmitic acid + 14 NADP+ + 7 COz + 8 CoA + 6 Hz0 (1). Acetyl-CoA serves as a primer for the reaction, and it is incorporated into the methyl end of the palmitic acid (2). The synthesis of palmitic acid is achieved through the formation of a series of intermediates covalently bound to protein (3-5). In this process, acetyl-enzyme is condensed with malonyl-enzyme to yield acetoacetyl-enzyme with the concomitant release of COZ. Acetoacetyl-enzyme is then reduced, dehydrated, and again reduced to butyryl-enzyme. The condensation, reduction, and dehydration reactions are repeated seven times, and each time a 2-carbon unit from malonyl-CoA is added to the intermediate acyl-enzyme compound. The formation of P-hydroxy-fl-methylglutaryl coenzyme A, 3,5diketohexanoic acid, and mevalonic acid is also effected by the partially purified pigeon liver fatty acid synthetase (3, 6). The pigeon liver enzyme was purified by Bressler and Wakil (1) to an activity of 0.3 pmole of NADPH oxidized per min per mg of protein. The integrity of this enzyme system was not established, however. In the current work, the fatty acid synthetase was purified to an activity of 1.0 pmole of NADPH oxidized per min per mg of protein. Enzyme of this activity behaves as a single homogeneous protein on sedimentation, on moving boundary electrophoresis, and on chromatography on diethylaminoethyl cellulose. This protein has a molecular weight of 5.4 x lo5 g per mole. It does not contain flavin, but it does contain at least 50 sulfhydryl groups. The purified fatty acid synthetase effects the formation of acetyland malonyl-enzyme from acetyland malonyl-CoA,