Antigenic regions of bovine somatotropin as defined by monoclonal antibodies

Three distinct antigenic regions of bovine somatotropin (bST) were identified on the basis of the ability of a set of monoclonal antibodies to bind to proteolytic fragments and deletion variants of recombinant bST (rbST) in Western blot analyses. One of the regions is further subdivided into two epitopes on the basis of the cross-reaction of somatotropins from several species with the same set of antibodies in solid-phase RIA. The RIA and Western blot results suggest that amino acids 134–150, 181–190 and the amino terminus may be involved in the binding specificity of antibodies to the bovine somatotropin molecule. The total of four antigenic regions on the bST molecule parallels results described for human somatotropin. Labeled antibody competition tests were used to show that the epitope involving amino acids 134–150 is spatially separated from the other three epitopes.