Phosphate transfer pathway substrate specificity

The ring nitrogen of pyridoxal phosphate exerts a strong electron-withdrawing effect on the aldimine, and this leads to weakening of all three bonds about the a-carbon of the substrate. In nonenzymic model systems, all the possible pyridoxal-catalyzed reactions are observed a-decarboxylation, amino-transfer, racemization, and side chain elimination and replacement reactions. By contrast, enzymes show specificity for the reaction pathway followed which bond is cleaved will depend on the orientation of the Schiff base relative to reactive groups of the catalytic site. 

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