Kwok C T, Pillay S P, Hardie I R
Biochem Biophys Res Commun. 1983 Nov 15;116(3):966-73. doi: 10.1016/s0006-291x(83)80236-8.
Cholesterol 7 alpha-hydroxylase when assayed under conditions that favour phosphorylation can be activated or inactivated by MgATP, depending on ATP concentration and the pH of the incubation medium. Maximum stimulation of 7 alpha-hydroxylase was obtained with 0.5 mM ATP in both acidic and alkaline pH. At a pH lower than 7.4, 7 alpha-hydroxylase was inactivated by 2.0 and 3.0 mM MgATP. The inactivation by 3 mM MgATP was significantly greater at pH 6.7 than pH 7.4. Protein kinases enhanced these effects, suggesting covalent modification of the enzyme by phosphorylation. These findings are consistent with a protein kinase catalyzed phosphorylation, and suggest that MgATP may have a dual role in the activation and inactivation of 7 alpha-hydroxylase in vivo.
在有利于磷酸化的条件下进行测定时，胆固醇7α-羟化酶可被MgATP激活或失活，这取决于ATP浓度和孵育介质的pH值。在酸性和碱性pH条件下，0.5 mM ATP均可使7α-羟化酶获得最大刺激。在pH低于7.4时，2.0 mM和3.0 mM MgATP可使7α-羟化酶失活。在pH 6.7时，3 mM MgATP引起的失活作用比pH 7.4时显著更强。蛋白激酶增强了这些效应，提示该酶通过磷酸化进行共价修饰。这些发现与蛋白激酶催化的磷酸化作用一致，并表明MgATP在体内7α-羟化酶的激活和失活过程中可能具有双重作用。
