Purification and characterization of a novel brain-specific 14-kDa protein

A new acidic protein specifically present in the brain was purified to homogeneity from bovine brain. The apparent molecular mass was estimated to be 14 kDa by sodium dodecyl sulfate-polyacrylamide gel electrophoresis, and 57 kDa by gel filtration, a finding suggesting that it exists as a tetramer under physiological conditions. The protein had a high content of Glu and Pro, and its pI was 4.3. The first six amino acid residues of the protein were Met-Asp-Val-Phe-Met-Lys, and the amino terminal was blocked. The distribution of the protein examined by Ouchterlony gel immunodiffusion indicates that it is present specifically in brain, including rat, human, and bovine, but could not be detected in 10 other rat tissues examined. The protein was absent in Purkinje cell bodies, as examined by electron microscopic immunocytochemistry, but was present in nerve terminals that make synapse-like contacts with Purkinje cells and in neurons with dark granules in the globus pallidus of the rat.