Inhibition studies of purple acid phosphatases: implications for the catalytic mechanism

Journal of the Brazilian Chemical Society

Mitic, Nataša¹  University of Queensland, St. Lucia, Australia¹  Schenk, Gerhard¹  Elliott, Tristan W.¹  Guddat, Luke W.¹  Gahan, Lawrence R.¹ 

关键词: purple acid phosphatase;    catalytic mechanism;    kinetics;    enzyme inhibition;   

DOI  :  10.1590/S0103-50532006000800011

学科分类：化学（综合）

来源: SciELO

【 摘 要 】

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.

【 授权许可】

Unknown