Highly Acidic Proteins from Human Brain: Purification and Properties of Glu-50 Protein

Abstract

Three extremely acidic proteins were isolated from human brain and purified to apparent homogeneity. One of them, Glu-50 protein, contained much glutamic acid (about 50% of the total amino acids). Its purification involved ammonium sulfate fractionation, DEAE-Sephadex α-50 chromatography, and gel filtration on Sephadex G-100 and G-75. Its molecular weight was determined to be 11,000 by SDS polyacrylamide gel electrophoresis and 34,000–36,000 by gel filtration on Sephadex G-75, suggesting that it consists of three identical polypeptide chains. Its isoelectric point was pH 3.9. Its N-terminal amino acid sequence was NH₂-Asp-Glu-Pro-Pro-Asp-Glu and its C-terminal amino acid was Lys. It contained no detectable carbohydrate.