Heterogeneity of human alpha-fetoprotein as revealed by isoelectric focusing in urea-containing gels.

The heterogeneity of human alpha-fetoprotein has been studied by analytical isoelectric focusing in polyacrylamide gel slabs in the presence of 8 M urea. Six major isoelectric variants could be identified over a pH range of 6.0--6.2. Verification of their identity was achieved by crossed immunoelectrophoresis into agarose gel containing monospecific antiserum to human alpha-fetoprotein. Complete desialylation of the protein did not abolish the heterogeneity; a complex pattern of major alpha-fetoprotein bands persisted over a more alkaline pH range. We have been able to correlate the pattern of alpha-fetoprotein heterogeneity seen following extended agarose gel electrophoresis with that obtained during isoelectric focusing in the presence of urea. The quantity of certain alpha-fetoprotein charge isomers in various alpha-fetoprotein isolates may be important in considering certain biological functions of this protein.