Analogues of intermediates in the action of pig kidney prolidase.

Dicarboxylic acids, resembling the collected substrates for the reverse peptide bond forming reaction, were bound several orders of magnitude more tightly than substrates, products, or previously known competitive inhibitors of reactions catalyzed by pig kidney prolidase (EC 3.4.13.9), a dipeptidase that cleaves peptide bonds to the nitrogen atom of proline. Other inhibitors containing a phosphoryl or phosphonyl group in addition to a carboxyl substituent were bound even more tightly, in a manner consistent with their possible resemblance to tetrahedral intermediates in substrate hydrolysis. These included several analogues of phosphoenol pyruvate, of which the most potent was (Z)-3-bromophosphoenolpyruvate (Ki = 4.6 x 10(-9) M). Ki values were found to vary with changing pH in a manner consistent with displacement of a hydroxide ion from the active site.