Metal Displacement Effects on Monoesterase Activity of Calf Intestinal Alkaline Phosphatase
No Thumbnail Available
Date
2012
Journal Title
Journal ISSN
Volume Title
Publisher
Nigerian Society of Biochemistry and Molecular Biology
Abstract
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.
Description
Keywords
Alkaline phosphatase, monoesterase reaction, metal ion cofactors, displacement reaction