期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：1983
卷号：80
期号：8
页码：2175-2178
DOI：10.1073/pnas.80.8.2175
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：A loss in cholesterol 7 alpha-hydroxylase activity [cholesterol 7 alpha-monooxygenase; cholesterol,NADPH:oxygen oxidoreductase (7 alpha-hydroxylating), EC 1.14.13.17 ] was seen when rat liver microsomes were incubated in the presence of Ca2+, Mg2+, or Mn2+. The loss in enzyme activity was complete within only 5 min of incubation with Ca2+ and Mn2+, whereas Mg2+ required 10 to 15 min of incubation with microsomes to produce a similar inhibition. This effect of metal ions could be blocked if the incubations were carried out in phosphate buffer. Similarly, preincubation of microsomes in the presence of NaF completely prevented the loss in enzyme activity due to Ca2+ and Mg2+ ions, but only partially the loss due to Mn2+. These results suggest metal ion activation of an endogenous microsomal phosphatase, which in turn may inactivate cholesterol 7 alpha-hydroxylase through its dephosphorylation. Further, a dialyzable microsomal factor appears to be essential for stabilizing the enzyme, because dialysis of a microsomal suspension results in a considerable loss of enzyme activity.
