Adenylate cyclases in two populations of membranes purified from neuroblastoma X glioma hybrid (NG 108-15) cells.

Abstract

Membranes from neuroblastoma X glioma NG108-15 hybrid cells were purified by equilibrium centrifugation on continuous and discontinuous gradients of sorbitol, using homogenates of cells which were pretreated with concanavalin A to increase membrane density. Adenylate cyclase was purified 24-fold in a heavy (H) membrane fraction from discontinuous gradients, opiate-stimulated guanosine-5'-triphosphatase was purified 3-fold, and opiate binding to receptors was increased 10-fold in this fraction. The relative purification of this membrane fraction is also verified by the fact that it contains a single protein (Mr = 58,000) which is covalently labeled by a reactive opiate analog (Klee, W. A., Simonds, W. F., Sweat, F. W., Burke, T. R., Jacobson, A. E., and Rice, K. C. (1982) FEBS Lett. 150, 125). The method of plasma membrane purification after cell treatment with concanavalin A (Lutton, J. K., Frederich, R. C. Jr., and Perkins, J. P. (1979) J. Biol. Chem. 254, 11181) appears generally applicable as established here with 3H-concanavalin A. Between 15 and 20% of the adenylate cyclase in whole-cell homogenates was recovered at low densities in continuous and discontinuous gradients and was only purified 2-fold above activity in the cell homogenate. There are significant differences between ligand binding, adenylate cyclase, and GTPase activities in light (L) and heavy (H) membrane fractions. GTPase activity in the L-membrane fraction was decreased from that in the cell homogenate and was not stimulated by opiates. Adenylate cyclase from L-membranes is only slightly inhibited by opiates in support of other data relating opiate inhibition to stimulation of GTPase (Koski, G., and Klee, W. A. (1981) Proc. Natl. Acad. Sci. 78, 4185).