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Inhibition Studies of Purple Acid Phosphatases: Implications for the Catalytic Mechanism

Elliott, Tristan W. and Mitic, Natasa and Gahan, Lawrence R. and Guddat, Luke W. and Schenk, Gerhard (2006) Inhibition Studies of Purple Acid Phosphatases: Implications for the Catalytic Mechanism. Journal of the Brazilian Chemical Society, 17 (8). pp. 1558-1565. ISSN 0103-5053

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Abstract

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.

Item Type: Article
Additional Information: 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 .
Keywords: purple acid phosphatase; catalytic mechanism; kinetics; enzyme inhibition;
Subjects: Science & Engineering > Chemistry
Item ID: 3711
Identification Number: /10.1590/S0103-50532006000800011
Depositing User: Gary Schenk
Date Deposited: 30 May 2012 15:50
Journal or Publication Title: Journal of the Brazilian Chemical Society
Publisher: Sociedade Brasileira de Química
Refereed: Yes
URI:

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