Similarities between Protein IIIa and Protein IIIb, Two Prominent Synaptic Vesicle-Associated Phosphoproteins (Journal Version)

摘要

Protein IIIa (Mr 74,000) and protein IIIb (Mr 55,000) are two major phosphoproteins found in mammalian brain. It was previously shown in intact nerve cells that the phosphorylation state of these two proteins could be increased by electrical stimulation, by depolarizing agents in the presence of calcium, and by 8-bromo-cAMP. The authors now report that protein IIIa and protein IIIb possess significant structural homology as indicated by immunochemical studies using polyclonal and monoclonal antibodies and by peptide mapping studies. A quantitative radioimmunoassay using immunolabeling in SDS-polyacrylamide gels has been used to study the tissue distribution and regional and subcellular distribution in the brain of the two proteins. The two proteins were found only in nervous tissue and the adrenal medulla. Within the central nervous system, both proteins exhibited a distribution that parallels the relative density of nerve terminals. Subcellular fractionation studies indicated that both proteins are associated with synaptic vesicles. (Copyright (c) 1987 Society for Neuroscience.)