Kinetic Analysis of Vanadium Inhibition on the Ni²⁺-stimulated Calcineurin Enzyme Activity

Abstract

Calcineurin (CN) is a Ca²⁺/calmodulin-binding protein serine/threonine phosphatase that plays a pivotal role in a variety of cellular functions, such as immune and nerve systems in our body. It is well known that the phosphatase activity is stimulated by Ni²⁺ and Mn²⁺ ions in vitro . Previously, we examined the effect of three types of vanadium ion, orthovanadate ions (VO₄^3-), metavanadate ions (VO₃^-) and vanadyl ions (VO²⁺) on Ni²⁺-stimulated phosphatase activity of CN. We have found that Ni²⁺-stimulated CN activity was inhibited by VO₄^3-, VO₃^- or VO²⁺. In the present study, we further examined effect of vanadium ions (VO₄^3- or VO₃^-) inhibition on the kinetics of Ni²⁺-stimulated CN activity. It has been shown that VO₄^3- and VO₃^- inhibitions of Ni²⁺-stimulated phosphatase were competitive inhibition using Lineweaver-Burk plot. Inhibition constants (Ki) for VO₄^3- and for VO₃^- were seen at 4.76 μmol/L and 7.16 μmol/L, respectively.