Purification and characterization of B-Protein from human serum

B-Protein, present in the serum of individuals with cancer, has been purified to electrophoretic homogeneity. The purification procedure consisted of chromatography on Sephacryl S-200, Affi-Gel Blue, Con A-Sepharose 4B, wheat germ lectin-Sepharose and preparative polyacrylamide gel electrophoresis. The molecular weight of B-Protein is estimated to be 100 000 to 120 000. It is a glycoprotein which appears to be composed of two subunits, each with a molecular weight of approximately 52 000. Analytical polyacrylamide gel electrophoresis and analytical ultracentrifugation data indicate that purified B-Protein is homogenous. Isoelectric focusing studies also show the purified B-Protein to be homogenous in composition consisting of a single band of p I = 4.8. Amino acid analysis is consistent with this acidic isoelectric point. Other analyses that B-Protein contains 7% carbohydrate and 7% lipid in the form of triglycerides.