Studies on α2-Macroglobulin in Bovine Plasma

Bovine plasma α₂-macroglobulin was purified from pseudoglobulin fraction by a combination of chromatographies on DEAE-Sephadex A-50 and CM-cellulose, and gel filtrations on Sephadex G-150 and Sepharose 4B. By these procedures, 1.2 g of purified preparation could be obtained from two liters of bovine plasma. The purified material was homogeneous as judged by immunoelectrophoresis, starch gel and disc electrophoresis, isoelectric focusing and ultracentrifugation. The α₂-macroglobulin was characterized in terms of its major physical and chemical properties. The molecular weight was determined to be approximately 800,000, and the $s20,w•$ value 17.8S, the $D20,w•$ value 1.93×10⁻⁷ cm²/sec, and the value 0.72 were obtained. The isoelectric point of this protein was found to be pH 5.07 indicating that the protein is acidic. The polypeptide portion of α₂-macroglobulin consisted of 6, 519 amino acid residues and was poor in half-cystine and tryptophan residues. A net negative charge was calculated as 97 from the amino acid analysis and this value was in good accordance with the acidic nature of the protein. The carbohydrate composition was determined to be hexose, 4.50%, glucosamine, 3.14%, sialic acid, 0.1%, and the molar ratio of mannose to galactose was 1: 1. From these results, it was concluded that α₂-macroglobulins of human, porcine and bovine plasmas resemble for each other with respect to their physical and chemical properties.