Purification and characterization of a liver-specific antigen.

A liver-specific antigen (F-antigen) previously demonstrated in saline extracts of BALB/c mouse liver by double immunodiffusion was isolated and characterized. The antigen was found widely distributed among mammals but absent from avian and frog liver extracts. In immunoelectrophoresis it had an electrophoretic mobility similar to that of serum beta2-globulins, was relatively thermolabile, and was precipitated at 30 to 70% saturated ammonium sulfate concentrations. Evidence was presented that this antigen is a protein or a moiety closely associated with protein. Gel-filtration on Sephadex G-200 revealed liver-specific antigenicity in the second peak. Ion-exchange chromatography on DEAE-Sephadex A-50 revealed four peaks of which only the third one exhibited liver-specific antigenicity. This active peak contained 11 polypeptides on SDS polyacrylamide gel electrophoresis. After electrophoresis on acrylamide gel in the absence of SDS, antigenic activity was detected on one fast-moving band. Extraction of the protein band followed by SDS gel electrophoresis showed one major component of m.w. 75,000 and two major bands of m.w. 72,000 and 93,000, respectively.