Study on physiological function of a brainspecific 14 kDa protein (PNP 14)

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A novel brain-specific protein with a molecular mass of 14 kDa was found and purified from bovine crebral cortex. In the present work, the primary structure of PNP 14 was determined. This protein is composed of 134 amino acid residues (molecularmass = 14,122 Da). We found that the protein was phosphorylated in*2+*vivo as well as in vitro. In vitro experiments showed that Ca*, calmodulin-dependent protein kinase II is responsible for the phosphorylation of Ser118, and tyrosine kinases such as EGF receptors and pp60^<v-src> catalyze tyrosine phosphorylation of PNP 14. The phosphorylation site of PNP 14 phosphorylated by EGF receptors was Tyr39. PNP 14 formed complex with phosphtidylinositol 3-kinase or pp60^<c-src>. Localization of PNP 14 and its mRNA expression in rat brain were investigated by immunohistochemistry and in situ hybridization. PNP 14 immunoreactivity was detected in cerebellar cortex. No PNP 14 immunoreactivity was detected in cerebellar medulla. In cerebrum, the immunoreactivity was found throughout cerebral cortex, especially in the layr V.It was also found in hippocampus and striatum. Electron microscopic observation revealed that the immunoreactivity was detected in the cytoplasmic matrix in the presynaptic axon terminals. PNP 14 mRNA was observed in granular layr of cerbellar cortex, hippocampus and cerebral cortex. These findings suggested that PNP 14 play important role in presynaptic axon terminals and the function is regulated by phosphorylation reaction.