Human -fetoprotein. Isolation, characterization, and demonstration of microheterogeneity.

Abstract Human α-fetoprotein has been isolated from the sera of hepatoma patients by the combined techniques of preparative electrophoresis, Sephadex gel filtration, and preparative isoelectric focusing. The purity of the isolated α-fetoprotein was demonstrable by (a) a single line on Ouchterlony immunodiffusion versus anti-α-fetoprotein, with no reaction versus a potent polyvalent anti-human serum of anti-albumin; (b) a single band on sodium dodecyl sulfate polyacrylamide electrophoresis; and (c) the production of monospecific antibody upon immunization of rabbits. The molecular weight of α-fetoprotein was 72,000 by sodium dodecyl sulfate acrylamide electrophoresis. Two major molecular forms of α-fetoprotein were found by isoelectric focusing, ion exchange chromatography, and agarose electrophoresis. Both forms were present in most hepatoma and fetal sera, but their relative amounts appeared to have no relationship to gestational age, clinical status, serum concentration, or method of storage. The two forms, with isoelectric points of 4.85 and 5.2, were isolated by preparative isoelectric focusing and were found to convert to a single homogeneous form with slower electrophoretic mobility after treatment with neuraminidase.