Kwok C T, Burnett W, Hardie I R
J Lipid Res. 1981 May;22(4):570-9.
Microsomal cholesterol 7 alpha-hydroxylase (EC 1.14.13.7) in rat liver was assayed by a single-isotope-incorporation method, and factors influencing its activity were studied. Crude cytosol contained a non-catalytic activator which was heat-stable and on-dialyzable. This activator enhanced cholesterol 7 alpha-hydroxylase catalytic activity. The stimulatory property of this cytosolic activator was not altered by cholestyramine feeding, and was retained after fractionation by ammonium sulfate of saturation up to 65%. 3-Hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) stimulated hydroxylase activity at concentrations up to 90 micro M. ATP at concentration greater than 1.2 mM inhibited hydroxylase activity. NaF was stimulatory at concentrations up to 50 mM with a maximum stimulatory effect at 10 mM, and was antagonistic in effect to ATP. HMG-CoA and ATP at the above inhibitory concentrations and higher abolished the activating effect of the cytosolic factor.
采用单同位素掺入法检测大鼠肝脏微粒体胆固醇7α-羟化酶（EC 1.14.13.7），并研究影响其活性的因素。粗制胞质溶胶含有一种非催化激活剂，该激活剂耐热且不可透析。这种激活剂可增强胆固醇7α-羟化酶的催化活性。喂食消胆胺不会改变这种胞质激活剂的刺激特性，且在饱和度高达65%的硫酸铵分级分离后仍能保留其特性。3-羟基-3-甲基戊二酰辅酶A（HMG-CoA）在浓度高达90微摩尔时刺激羟化酶活性。浓度大于1.2毫摩尔的ATP抑制羟化酶活性。氟化钠在浓度高达50毫摩尔时具有刺激作用，在10毫摩尔时具有最大刺激作用，且对ATP具有拮抗作用。上述抑制浓度及更高浓度的HMG-CoA和ATP消除了胞质因子的激活作用。
