A palmityl-CoA synthetase stimulating factor of particle free supernatants

Abstract

1. 1.|A factor in the particle-free supernatant of tissue homogenates has been shown to stimulate palmityl-CoA synthetase (acid:CoA ligase (AMP), EC 6.2.1.3) in particulate subcellular fractions. The factor is a heat-labile, (NH 4) 2SO 4-precipitable macromolecule, probably a protein. 2. 2.|By repeated fractionation with (NH 4) 2SO 4, the factor has been obtained almost free from contaminating palmityl-CoA synthetase in the supernatant. 3. 3.|The factor has been found in several organs of the rat, and in livers from animals of different species. The factor from different organs and species stimulated the palmityl-CoA synthetase in all organs tested. 4. 4.|It is shown that the effect of the stimulating factor obtained in the supernatant is to increase the formation of palmityl-CoA by the subcellular particulate fractions. 5. 5.|In the presence of the supernatant factor, maximum palmityl-CoA synthetase activity is obtained when ATP and Mg 2+ are added in approximately equimolar amounts. Excess ATP or excess Mg 2+ inhibits the stimulating effect of the supernatant factor. In the absence of the factor, excess ATP or excess Mg 2+ has no inhibiting effect on the synthetase activity. The supernatant factor does not change the requirements for CoA. 6. 6.|Preincubation of microsomes with supernatant in the presence of Mg 2+ and ATP activates the microsomal palmityl-CoA synthetase. 7. 7.|The possibility that the stimulating factor may be a palmityl-CoA synthetase kinase, is discussed.