Reinvestigation of extremely acidic proteins in bovine brain

Analysis of bovine brain extract by disc electrophoresis on a 20% polyacrylamide gel indicated the existence of three extremely acidic proteins. These proteins were isolated by column chromatography on DEAE-Sephadex A-50 and Sephadex G-75. The isolated proteins (PAP I-a, PAP I-b and PAP II) were homogeneous in various methods including 7.5% and 20% gel electrophoresis or gel chromatography, and share, in the extract, 85% of the total of the acidic proteins that migrate with the bromophenol blue marker in 7.5% gels. Their physicochemical properties, including molecular weight, ultraviolet absorption spectra or amino acid composition were similar, especially those between PAP I-a and PAP I-b where a part of primary structure appeared to be common in their tryptic peptide maps. These two proteins were identified to be the nervous system specific protein S 100 by immunochemical and electrophoresis methods as well as by amino acid analysis, and the other protein PAP II was revealed to be a calcium-binding protein. The existence and properties of the isolated proteins are discussed with relation to the heterogeneity problem of S 100 protein.