SUBCELLULAR-DISTRIBUTION OF GTP-BINDING PROTEINS, G0 AND G12, IN RAT CEREBRAL-CORTEX

The localization of GTP-binding protein (G-protein) subunits, Go, G12a and β, in subcellular fractions of rat cerebral cortex was determined by means of immunoassays specific for the respective subunits. High concentrations of all three subunits were observed in both crude mitochondrial and microsomal fractions. Muscarinic cholinergic receptors were also densely localized in these fractions. Then the crude mitochondrial and microsomal fractions were subfractionated by sucrose density gradient centrifugation. Each fraction obtained was evaluated morphologically by electron microscopy and biochemically by determination of membrane markers. The crude mitochondrial fraction was subfractionated into myelin, synaptic plasma membrane, and mitochondrial fractions. All the G-protein subunits examined and muscarinic receptors were exclusively localized in the synaptic plasma membrane fraction. Among the submicrosomal fractions, the heavy smooth-surfaced microsomal fraction showed the highest concentrations of all G-protein subunits and receptors, while the rough-surfaced microsomal fraction contained low amounts of them. The heavy smooth-surfaced microsomal fraction also contained high specific activity of (Na+-K+)-ATPase, a marker of the plasma membrane. These results indicated that the Go, Ga2 and β subunits are mainly localized in the plasma membrane in the brain. © 1990 COPYRIGHT, 1990 BY THE JOURNAL OF BIOCHEMISTRY.