Characterization of protein F1 (47 kDa, 4.5 pI): a kinase C substrate directly related to neural plasticity.

We recently demonstrated that long-term potentiation in rat hippocampal formation leads to a selective increase in the phosphorylation of a 47-kDa protein band (F1). The present report provided evidence, using two-dimensional gel electrophoresis, that only one major phosphoprotein in rat is found at 47 kDa under conditions identical to those used in that earlier study. This protein, which we also term F1, has an isoelectric point of 4.5 and is increased in phosphorylation after long-term potentiation. In addition to this identification, we demonstrated in two-dimensional gels that protein F1 is a membrane-enriched kinase C substrate whose phosphorylation is stimulated by Ca2+ and phosphatidylserine. Protein F1 may be equivalent to several reported proteins: a brain-specific, synaptically enriched protein (B-50), a major membrane-bound growth cone protein (pp46), and a fast axonally transported "growth-associated protein" (GAP43; 44- to 49-kDa goldfish optic nerve protein). Protein F1 participation in neural plasticity may thus involve growth occurring at synaptic loci.