CHARACTERIZATION OF MICROSOMAL CHOLOYL-COENZYME-A SYNTHETASE
CHARACTERIZATION OF MICROSOMAL CHOLOYL-COENZYME-A SYNTHETASE
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DOI：
10.1042/bj1630357
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发表时间：
1977-01-01
影响因子：
4.1
通讯作者：
ZAKIM, D
中科院分区：
文献类型：
--
作者：
VESSEY, DA;ZAKIM, D
在适当的试验条件下首次表征胆酰辅酶A合成酶（EC 6.2.1.7）[豚鼠肝脏]。反应的最适pH为pH 7.2-7.3。该反应对二价阳离子有绝对的要求。几种不同的金属离子满足这一要求，但Mn 2+和Mg 2+是最有效的。The .**图形 **。从动力学数据外推的CoA的Km（表观Km）为50 μ M，但事实上，CoA浓度高于25 μ M时，反应速率几乎没有增加。The .**图形 **。ATP的浓度为600 μ M。高浓度的ATP似乎引起底物抑制。The .**图形 **。胆酸盐的浓度为6 μ M。通过用N-乙基马来酰亚胺处理微粒体部分来抑制酶。在试验中加入各种结合和非结合胆汁盐也可抑制酶。非结合胆汁盐比结合胆汁盐具有更强的抑制作用。高浓度的油酸抑制该酶。胆酰辅酶A合成酶的性质没有修改的微粒体膜的脂质相的性质的改变。用磷脂酶A处理不直接改变活性。Triton N-101和Triton X-100也对活性没有影响，并且该酶对膜的脂质部分内的温度诱导的相变不敏感。通过用Triton N-101处理，酶可以以活性形式从微粒体膜中溶解。
Choloyl-CoA synthetase (EC 6.2.1.7) [guinea pig liver] was characterized for the 1st time under appropriate assay conditions. The pH optimum for the reaction is pH 7.2-7.3. The reaction has an absolute requirement for bivalent cation. Several different metal ions fulfil this requirement, but Mn2+ and Mg2+ were the most effective. The .**GRAPHIC**. (apparent Km) for CoA, extrapolated from kinetic data, is 50 .mu.M, but in fact the rate of reaction is increased little by concentrations of CoA above 25 .mu.M. The .**GRAPHIC**. for ATP is 600 .mu.M. High concentrations of ATP appear to cause substrate inhibition. The .**GRAPHIC**. for cholate was 6 .mu.M. The enzyme was inhibited by treating the microsomal fraction with N-ethylmaleimide. The inclusion of various conjugated and unconjugated bile salts in the assay also inhibited the enzyme. Unconjugated bile salts were more potent inhibitors than the conjugated bile salts. High concentrations of oleic acid inhibited the enzyme. The properties of choloyl-CoA synthetase were not modified by alterations of the properties of the lipid phase of the microsomal membrane. Treatment with phospholipase A did not alter activity directly. Triton N-101 and Triton X-100 also were without effect on activity, and the enzyme was insensitive to temperature-induced phase transitions within the lipid portion of the membrane. The enzyme can be solubilized from the microsomal membrane in an active form by treatment with Triton N-101.