Characterization of two plasma membrane proteins abundant in rat brain.

Plasma membranes were isolated from rat brain cortices and their proteins characterized by two-dimensional electrophoresis. Approximately 500 polypeptides with relative molecular weights (mol. wt.) between 20 kDa and 120 kDa and isoelectric points (pI) between 4.2 and 8.5 were visualized by silver staining. Two proteins, MP1 and MP2, comprised about 5% each of the total by mass. Their mol. wts. were 56 kDa and 43 kDa, and their pIs were 4.2 and 4.3, respectively. The two proteins were present in membranes of cultured granule neurons and cortical astrocytes and absent in liver and kidney. They were both substrates for phosphorylation by protein kinase C. MP2 is similar, if not identical, to a major phosphoprotein in growth cones, pp46 (also termed GAP-43, B-50, F1).