Metal Displacement Effects on Monoesterase Activity of Calf Intestinal Alkaline Phosphatase

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Nigerian Society of Biochemistry and Molecular Biology


The mechanism of modulation of alkaline phosphatase activity by metal ions has not been fully elucidated. We investigated the time-dependent modulatory effects of Mg 2+ and Zn 2+ in promoting the hydrolysis of para-nitrophenyl phosphate (monoesterase reaction) by calf intestinal alkaline phosphatase (CIAP) and the effects of addition of the activating metal ions to the metal-inhibited enzyme. The CIAP was affected by changes in pre-incubation time in the presence of the two metal cofactors. Both Mg 2+ (0.1 – 0.25 mM) and Zn 2+ (0.1 – 5 mM) modulated Zn 2+ - and Mg 2+ - inhibited monoesterase activity of CIAP. The CIAP activity was inhibited when the enzyme was pre-incubated with 1 mM Ca 2+ . Further addition of Mg 2+ (0.1 – 2 mM) did not completely restore the activity though partly relieved the inhibition caused by Ca 2+ - pre-incubated enzyme. Again, addition of 2mM Zn 2+ to Ca 2+ - pre-incubated alkaline phosphatase completely restored the activity of the enzyme. This study suggests that Mg 2+ and Zn 2+ regulate the catalytic property of each other and modulate the inhibitory effect of Ca 2+ in alkaline phosphatase catalysis through a displacement effect. The modulation of Ca 2+ -inhibited CIAP activity by Mg 2+ and Zn 2+ may be explored in the treatment of disorders of bone mineralization especially those arising from inhibited alkaline phosphatase activity.



Alkaline phosphatase, monoesterase reaction, metal ion cofactors, displacement reaction