Inhibition of phosphatase and sulfatase by transition-state analogs

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Abstract
The inhibition constants for vanadate, chromate, molybdate, and tungstate have been determined with Escherichia coli alkaline phosphatase, potato acid phosphatase, and Helix pomatia aryl sulfatase. Vanadate was a potent inhibitor of all three enzymes. Inhibition of both phosphatases followed the order WO42- > MoO42- > CrO42-. The Ki values for potato acid phosphatase were about 3 orders of magnitude lower than those for alkaline phosphatase. Aryl sulfatase followed the reverse order of inhibition by group VI oxyanions. Phenol enhanced inhibition of alkaline phosphatase by vanadate and chromate but did not affect inhibition of acid phosphatase. Phenol enhanced inhibition of aryl sulfatase by metal oxyanions in all cases following the order H2VO4- > CrO42- > MoO42- > WO42-, and N-acetyltyrosine ethyl ester enhanced inhibition of aryl sulfatase by H2VO4- and CrO42- more strongly than did phenol. It is apparent that the effectiveness of metal oxyanions as inhibitors of phosphatases and sulfatases can be selectively enhanced in the presence of other solutes. The relevance of these obervations to the effects of transition oxyanions on protein phosphatases in vivo is discussed.