The antibody-enzyme analogy. Comparison of enzymes and antibodies specific for phosphopyridoxyltyrosine.

Reduced Schiff base compounds of pyridoxal-P and tyrosine, which were used to induce specific antibodies described in the preceding article (V. Raso and B. D. Stolar, Biochemistry, 1975), caused active site-directed inhibition of tyrosine transaminase and tyrosine decarboxylase. The antibodies, studied as analogs of enzymes, were able to bind an unsaturated Schiff base catalytic intermediate, as shown by equilibrium dialysis and absorbance difference spectroscopy. Schiff base formation can proceed while the pyridoxal-P and tyrosine are within the antibody combining site, but the rate of this bimolecular condensation within the sites was not greater than the rate in free solution. Antibody did effect a small rate enhancement for the pyridoxal-P-catalyzed transamination of L-tyrosine. These results are discussed in light of current ideas in the mechanisms of enzyme catalysis.