Synthesis of Brain-Specific Acidic Proteins in Rat and Mouse Cerebral Slices

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Abstract
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.