Elliott, Tristan W. and Mitic, Natasa and Gahan, Lawrence R. and Guddat, Luke W. and Schenk, Gerhard
Inhibition Studies of Purple Acid Phosphatases: Implications for the Catalytic Mechanism.
Journal of the Brazilian Chemical Society, 17 (8).
Purple acid phosphatases (PAPs) belong to the family of binuclear metallohydrolases and catalyse
the hydrolysis of a large group of phosphoester substrates at acidic pH. Despite structural conservation
in their active sites PAPs appear to display mechanistic versatility. Here, aspects of the catalytic
mechanism of two PAPs are investigated using the inhibitors vanadate and fluoride as probes. While
the magnitude of their vanadate inhibition constants are similar the two enzymes differ with respect
to the mode of inhibition; vanadate interacts in a non-competitive fashion with pig PAP (Ki = 40
μmol L-1) while it inhibits red kidney bean PAP competitively (Ki = 30 μmol L-1). Similarly, fluoride
also acts as a competitive inhibitor for red kidney bean PAP, independent of pH, while the inhibition
of pig PAP by fluoride is uncompetitive at low pH and non-competitive at higher pH, independent of
metal ion composition. Furthermore, while fluoride acts as a slow-binding inhibitor in pig PAP it
binds rapidly to the catalytic site of the red kidney bean enzyme. Since vanadate and fluoride are
proposed to act as transition state and nucleophile mimics, respectively, the observed differences in
inhibition kinetics indicate subtle but distinct variations in the reaction mechanism of these enzymes.
||The definitive version of this article is available from the Journal of the Brazilian Chemical Society, Vol. 17, No. 8, 1558-1565, 2006, http://dx.doi.org/10.1590/S0103-50532006000800011 .
||purple acid phosphatase; catalytic mechanism; kinetics; enzyme inhibition;
||Science & Engineering > Chemistry
||30 May 2012 15:50
|Journal or Publication Title:
||Journal of the Brazilian Chemical Society
||Sociedade Brasileira de Química
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