Antigenic modification of polypeptides

Claim 1

A process for preparing an isoimmunogen for controlling biological action in an animal which comprises: activating a hormone endogenous to said animal, non-hormonal polypeptide endogenous to said animal or a synthetic or natural fragment of either having a sulfhydryl group thereon by treatment thereof with an activator of the structure ##STR16## where X represents a non-reacting group comprising substituted or unsubstituted phenyl or C 1-10 alkylene moieties, or a combination thereof, or an amino acid chain, so as to cause reaction of the maleiimide group of the activator with a said sulfhydryl group on said hormone, peptide or fragment and so as to minimize reaction of the active ester group with any amino group present on said hormone, peptide or fragment; and treating the resulting activated hormone, peptide or fragment at slightly alkaline pH with a carrier moiety biologically foreign to said animal and selected having a size sufficient to elicit antibody response following the administration thereof into the body of said animal.