Conscripting the active-site zinc ion in carboxypeptidase A in inactivation chemistry by a new type of irreversible enzyme inactivator

Article abstract of DOI:10.1021/ja00096a001

A new strategy for irreversible inactivation of the metalloenzyme carboxypeptidase A (CPA) involving a proposed activation of a carbon-iodide bond in an inactivator by the active-site zinc ion toward nucleophilic substitution is described. 2-Benzyl-3-iodopropanoic acid (compound 1) was designed to bind the active site of CPA. An energy-minimized complex of 1 in the active site of CPA reveals that the iodo moiety comes within the coordination sphere of the zinc ion. Such metal coordination was expected to facilitate the departure of the halide in an S(N)2-type reaction by the side-chain functions of either Glu-270 or Tyr-248. Compound 1 was shown to inactivate CPA in a time-dependent manner, a process which was active-site directed and irreversible; a rate enhancement of approximately 10⁸ to 10⁹-fold is estimated for the inactivation chemistry by 1 over model metal-activated S(N)2 type reactions. 2-Benzyl-4-iodobutanoic acid (compound 6), an analog of 1 with an extended structure by one methylene unit, was shown to serve solely as a poor competitive inhibitor for CPA (K(i) = 0.41 ± 0.07 mM) but not as an irreversible inactivator; a discussion of the kinetic behavior by the two compounds is provided. The results reported herein hold the promise of a novel chemistry for selective inactivation of metalloenzymes.