Browsing by Author "Olorunniji, F.J."

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    Catalytic cofactors (Mg2+ and Zn2+ ions) influence the pattern of vanadate Inhibition of the monoesterase activity of calf intestinal alkaline phosphatase
    (Nigerian Society for Experimental Biology, 2014) Igunnu, Adedoyin; Arise, R.O.; Adebayo, J.O.; Olorunniji, F.J.; Malomo, S.O.
    The mechanism of modulation of vanadate inhibition of alkaline phosphatase activity by catalytic cofactors has not been fully characterized. We investigated the effect of the interaction of catalytic cofactors (Mg2+ and Zn2+) and vanadate (an active site inhibitor) on the rate of hydrolysis of para-nitrophenyl phosphate (pNPP) (monoesterase reaction) by calf intestinal alkaline phosphatase (CIAP). The results showed that vanadate significantly inhibited ʻcofactor-freeʼ CIAP, and the inhibition was relieved by the presence of the catalytic cofactors in the reaction. Our results show that the absence of the cofactors did not significantly alter the Km of the reaction, but caused a decrease in the Vmax. Kinetic analyses showed that vanadate inhibited CIAP-catalyzed hydrolysis of pNPP by decreasing the Vmax and increasing the Km of the reaction. The presence of cofactors in the reaction alleviated the effect of vanadate by increasing the Vmax and decreasing the Km. The activity of the dialyzed CIAP was increased by the addition of catalytic cofactors to vanadate-inhibited enzyme. This study provides preliminary data that reversible inhibition of CIAP is subject to the influence of catalytic cofactors. Further studies will reveal detailed mechanistic aspects of this observation and its significance in the biological system.
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    Cofactor interactions in the activation of tissue non-specific alkaline phosphatase: Synergistic effects of Zn2+ and Mg2+ ions
    (Nigerian Society for Experimental Biology, 2007) Olorunniji, F.J.; Igunnu, Adedoyin; Adebayo, J.O.; Arise, R.O.; Malomo, S.O.
    The interactions of Mg2+ and Zn2+ ions in the activation of non-specific tissue alkaline phosphatase were investigated using crude extracts of rat kidney. Activation of alkaline phosphatase by the metal ions was accompanied by changes in the kinetic parameters of p nitrophenylphosphate hydrolysis. The results suggest some synergistic interactions between Mg2+ and Zn2+ ions in promoting the hydrolysis of p-nitrophenylphosphate by alkaline phosphatase. The results show that assays of alkaline phosphatase activity in homogenised tissue samples will give better responses if both Mg2+ and Zn2+ ions are included in the reactions.