Metabolism of Isolated Fat Cells

Abstract A procedure is described for preparing sacs of plasma membrane from free fat cells. The resultant spherical were essentially devoid of fat and contained 25% of the mitochondria, 2% of the soluble glycolytic enzymes measured (glucose 6-phosphate dehydrogenase, fructose 1,6-diphosphate aldolase, lactic dehydrogenase), and 15% of the hexokinase activity originally present in fat cells. A large fraction of the hexokinase activity was associated with particles. Some ghosts were nucleated, but all contained undefined particles and vesicles. The plasma membrane of ghosts was semipermeable to ions and sucrose and thus retained some of the characteristics of permeability shown by the plasma membrane of intact fat cells. Adenyl cyclase activity was found in ghosts and in a particulate fraction containing mitochondria released during lysis of fat cells. Ghosts contained 62% of the adenyl cyclase activity, with specific activities that averaged 2.5 times that found in the mitochondrial fraction. The enzyme was not dissociated from membranes by sonic oscillation. Adrenocorticotropin stimulated adenyl cyclase activity in both ghosts and mitochondria fractions, the effect of the hormone being greater on ghosts.