The immunological crossreaction between human alpha-fetoprotein and serum albumin and its relation with the binding ability.

Abstract

The crossreactivity between human α-fetoprotein and serum albumin in their unfolded forms was investigated by immunological methods. On enzyme immunoassay and immunostaining, reduced and carboxyamidomethylated human α-fetoprotein and serum albumin crossreacted with antibodies to their unfolded forms and weakly reacted with those to their native forms. Peptide fragments of human α-fetoprotein and serum albumin cleaved only by cyanogen bromide were nonreactive with antibodies to their native forms and with those to their unfolded forms. However, after reduction and carboxyamidomethylation, the peptide fragments prepared were mostly crossreactive with antibodies of their unfolded forms, but not with those of their native forms. While the native forms of human α-fetoprotein and serum albumin and their peptide fragments obtained by cyanogen bromide cleavage retained binding abilities with bilirubin and anilinonaphthalene sulfonate, the unfolded forms had no binding abilities. These findings suggest that the binding abilities, proposed to be related to the biological functions of human α-fetoprotein and serum albumin, are mainly attributable to their conformational character rather than to their primary sequences.