Physicochemical Properties of Bovine Mammary Fatty Acid Synthetase

• Published in: The Journal of biological chemistry 1974-01, Vol.249 (1), p.118-125
• Main Authors: Maitra, Shyamal K., Kumar, Soma
• Format: Article
• Language: English
• Subjects: animal science; livestock; zoology
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1016/S0021-9258(19)43099-8

Fatty acid synthetase from lactating bovine mammary gland has an s020, w of 13.5 and a molecular weight of 530,000 as determined by sedimentation equilibrium. This enzyme is not cold-labile and can be stored at 4° with little loss in enzyme activity for up to 2 weeks in 0.25 m potassium phosphate buffer, pH 6.8, containing 1.0 mm dithiothreitol in an atmosphere of N2. At room temperature the activity was lost in 3 days. In Tris (10mm)-glycine (35 mm) buffer, pH 8.45, the enzyme dissociated completely in about 27 hours into obviously nonidentical, but inseparable 9 S subunits with molecular weights of 220,000 with a loss of most of the fatty acid synthetase and crotonyl-CoA reductase activities. On filtration of these subunits through Sephadex G-50, equilibrated with 0.25 m potassium phosphate buffer, pH 6.8, containing 10-3m dithiothreitol, they reassociated with partial recovery of both fatty acid synthetic and crotonyl-CoA reductase activities. Prolonged dialysis of the enzyme against Tris buffer resulted in the loss of both activities completely. The ressociation, as judged by the recovery of the two activities of the enzyme, then took 14 to 19 days to be accomplished. The various size-shape parameters are consistent with a model in which the two half-molecular rod-shaped subcomplexes are held together in the native enzyme complex head to head with the catalytic sites of all the constitutive enzymes of the complex juxtaposed near each other. The crotonyl-CoA reductase activity is also believed to occur at a nearby site as the structural integrity of the native enzyme complex is essential for this activity also.