Distinct Metal Ion Requirements for the Phosphomonoesterase and
Phosphodiesterase Activities of Calf Intestinal Alkaline Phosphatase
Adedoyin Igunnu1, Dunsin S Osalaye2, Olufunso O Olorunsogo2, Sylvia O Malomo**, 1, Femi J Olorunniji*, 1, 3
1 Department of Biochemistry, Faculty of Science, University of Ilorin, Ilorin, Nigeria
2 Department of Biochemistry, College of Basic Medical Sciences, University of Ibadan, Ibadan, Nigeria
3 Institute of Molecular Cell and Systems Biology, University of Glasgow, Bower Building, Glasgow G12 8QQ, Scotland,
The roles of Mg2+ and Zn2+ ions in promoting phosphoryl transfer catalysed by alkaline phosphatase are yet to be fully characterised. We investigated the divalent metal ion requirements for the monoesterase and diesterase activities of calf intestinal alkaline phosphatase. The synergistic effect of Mg2+ and Zn2+ in promoting the hydrolysis of para-nitrophenyl phosphate (monoesterase reaction) by alkaline phosphatase is not observed in the hydrolysis of the diesterase substrate, bis-para-nitrophenyl phosphate. Indeed, the diesterase reaction is inhibited by concentrations of Mg2+ that were optimal for the monoesterase reaction. This study reveals that the substrate specificities of alkaline phosphatases and related bimetalloenzymes are subject to regulation by changes in the nature and availability of cofactors, and the different cofactor requirements of the monoesterase and diesterase reactions of mammalian alkaline phosphatases could have significance for the biological functions of the enzymes.
Keywords: Alkaline phosphatase, phosphodiester hydrolysis, metal ion cofactors.
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* Address correspondence to these authors at the Institute of Molecular Cell
and Systems Biology, University of Glasgow, Bower Building, Glasgow
G12 8QQ, Scotland, UK; Tel: +441413303331;
E-mail: Femi.Olorunniji@glasgow.ac.uk** Department of Biochemistry, Faculty of Science, University of Ilorin, Ilorin,
Nigeria; Tel: +2348033736997; E-mail: email@example.com