Synthesis of brain-specific acidic proteins in rat and mouse cerebral slices

Optimal conditions for incorporation of radioactive amiino acids into protein by slices of brain have been established. Protein synthesis continued for at least 4 h at 35 degrees. The highest incorporation of amino acids into protein was obtained with 20-50 mg wet weight per ml incubated at pH 7.1. After incubation of 500 mg of slices acidic proteins were separated by saltfractionation and electrophoresis on 14% polyacrylamide gel. The most acidic band was shown to contain S-100 protein. Indentification was solubility of the protein in 100% (NH4)2SO4, electrophoretic mobility at pH 8.9, precipitation with specific antibodies, and 2-dimensional electrophoresis in polyacrylamide gel. The protein band was insoluble in 50% methanol and contained between 0.06 and 0.2% of the radioactivity present in the total soluble proteins; while other well separated acidic proteins contained about 10 times the radioactivity of S-100 protein.