Diesterase Activity and Substrate Binding in Purple Acid Phosphatases
Cox, Robynn S. and Schenk, Gerhard and Mitic, Natasa and Gahan, Lawrence R. and Hengge, Alvan C. (2007) Diesterase Activity and Substrate Binding in Purple Acid Phosphatases. Journal of the American Chemical Society, 129 . pp. 9550-9551.
Purple acid phosphatases (PAPs) are dinuclear monoesterases1,2 that are structurally diverse but with a conserved set of ligands to the Fe3+-M2+ metal centers (M2+ ) Fe, Zn, or Mn).3 The identity of the nucleophile and the substrate binding mode have been matters of controversy (Figure 1).1,3-5 In one proposal, substrate binds to the divalent metal and is attacked by a terminal Fe3+-bound hydroxide. In an alternative mechanism, substrate coordinates first to the divalent metal and then forms a bridging complex, followed by nucleophilic attack by the í-hydroxide. We report that the PAPs from pig and kidney bean catalyze the hydrolysis of diesters if the second ester group is small, and the kinetics of the reaction with methyl p-nitrophenylphosphate suggest that a terminal-bound hydroxide is the nucleophile for the diester, followed by attack of the bridging hydroxide upon the resulting monoester without release into solution.
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