They irreversibly inhibit the proton pump molecule and hence,acid secretion requires synthesis of new proton pumps(ref Rang and Dale 5/e p370-371, goidman gilman 12/e p1311-1312) The activated form of PPI binds covalently with sulfahydryl groups of cysteine in the H+ K+ atpase ,irreversbly inacativating the pump molecule.acid secretion resumes only after new pump molecules are synthesized and inseed into the luminal membranes ptoviding a prolonged suppresion of acid secretion despite the much shoer pladma half lives of the parent compounds.