An analog-ligand having a conformation that substantially corresponds to the conformation of a hydrolytic transition state of an amide or ester reactant ligand is used to produce receptor molecules of predetermined specificity. The receptor molecules include an antibody combining site that binds to a reactant ligand and thereby stabilizes the tetrahedral carbon atom of the amide or ester hydrolysis transition state of that reactant ligand to catalytically hydrolyze the reactant ligand at a predetermined site.