Nonenzymatic Hydrolysis of Adenosine 5′-Triphosphate in Micellar and Reversed Micellar Systems

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Abstract
The nonenzymatic hydrolysis of adenosine 5′-triphosphate (ATP) in micellar and reversed micellar system was examined as an approach to elucidate the function of ATPase. In aqueous micellar systems an anionic surfactant does not affect the hydrolysis rate, but a cationic surfactant, cetyltrimethylammonium bromide(CTAB), retards the hydrolysis. This deceleration effect is interpreted to be owing to the pH change or accumulation of hydroxide ions at the cationic micellar-water interface which serves as reaction site. In the reversed micellar system where aqueous ATP phase is solubilized in n-hexane by dodecylammonium propionate(DAP), the hydrolysis rate of ATP is enhanced by several times as compared with that in an aqueous system. Addition of Mg2+ or Ca2+ enhances the hydrolysis rate markedly only in the DAP reversed micellar system. The catalytic effect of the DAP reversed micellar system is discussed with respect to the polarity of water phase solubilized in the core of reversed micelles.