A rat serum glycoprotein whose synthesis rate increases greatly during inflammation

Abstract

Crossed immunoelectrophoresis of rat serum demonstrated considerably increased serum concentrations of at least ten different proteins during turpentine-induced inflammation. One protein, which moved during electrophoresis like an α1 globulin, showed a particularly large increase. This protein was purified to homogeneity by ammmonium sulfate fractionation followed by chromatography on DEAE-cellulose, Sephadex G-100, and concanavalin A-Sepharose, and finally disc electrophoresis in polyacrylamide gel. It has a molecular weight of 56,000 determined by equilibrium ultracentrifugation. An apparent molecular weight of 68,000 was estimated for the reduced protein by electrophoresis in polyacrylamide gel plus sodium dodecyl sulfate, suggesting that the native protein is composed of a single polypeptide chain. It has an E(1%)(280, 1cm) of 5.2, an isoelectric pH of 4.7 and contains 19% carbohydrate. The protein does not inhibit bovine trypsin or chymotrypsin. Its physical properties and amino acid composition distinguish this protein from all other rat serum proteins hitherto characterized. During acute inflammation, induced 25 h previously, rats incorporated 20 times more [14C]leucine into this particular protein than did normal rats. However, incorporation into total serum protein during acute inflammation increased only slightly. Regardless of whether inflammation was induced by surgical injury or by a subcutaneous turpentine injection, within 48 h the serum concentration of this major acute-phase protein rose from the normal value of 0.46 g/liter to a maximum value of 7.2 g/liter, which constituted 10% of the total serum protein.