Fatty Acid Synthetase from Lactating Rat Mammary Gland

Fatty acid synthetase has been purified from lactating rat mammary gland and some of its physical and kinetic properties studied. This synthetase is an asymmetrical multienzyme complex of molecular weight 478,000 which readily dissociates into approximately half-molecular weight subunits. The sedimentation and diffusion coefficients of the native enzyme are 12.9 set X lo-l3 and 2.56 cm2 se@ X lo-‘, respectively. The enzyme contains one 4’-phosphopantetheine residue and approximately 56 sulfhydryl groups per mole. Under optimum assay conditions, palmitic acid is the major product. With respect to size, shape, 4’-phosphopantetheine content, turnover number, and products of the reaction, the enzyme is very similar to the fatty acid synthetases purified from pigeon and rat liver. Studies of the kinetic properties, however, have revealed several differences in the Michaelis-Menten constants and inhibition and activation characteristics of the fatty acid synthetases from mammary gland and liver.