The diversity of the immune response, which can provide a panel of catalytic antibodies with varying degrees of catalytic activity and substrate specificity by immunization with a single hapten,raises the question concerning the extent to which a rationally designed hapten dictates the paratopes for catalytic function in the antigen-combining site. We have investigated the biochemical properties within a panel of six hydrolytic catalytic antibodies elicited against a phosphonate transition state analog 3 and:have examined the correlation between the functions and the antigen-combining-site structures. Although the individual values for k(cat), K-m, and K-TsA (the affinity for the transition state analog) of the six antibodies differed substantially, the transition state analysis (k(cat)/k(uncat) versus K-S/K-TSA) displayed a linear relationship (slope = 0.99) with the four antibodies 6D9, 8D11, 4D5, and 9C10, which have homologous primary amino acid sequences,providing evidence that all of the differential binding energy of the transition state vs the ground state is available for the rate enhancement. This also suggested that these four antibodies catalyze the hydrolysis by variations of the same basic mechanism of transition state stabilization.