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Acyl-coenzyme A--cholesterol acyltransferase activity in human liver
Clinical Science (London, England : 1979)
|April 1, 1979
Summary
Human liver microsomes contain cholesterol acyltransferase (ACAT), an enzyme crucial for cholesterol esterification. This enzyme exhibits distinct substrate utilization compared to its rat counterpart, with lower activity in human liver tissue.
Area of Science:
- Biochemistry
- Enzymology
- Human Physiology
Background:
- Cholesterol esterification is a key process in cellular lipid metabolism.
- Acyl-coenzyme A-cholesterol acyltransferase (ACAT) plays a vital role in this process.
- Understanding ACAT in human liver is important for metabolic research.
Purpose of the Study:
- To demonstrate the presence and characterize the activity of cholesterol acyltransferase (ACAT) in human liver microsomes.
- To compare the properties of human liver ACAT with those of rat liver ACAT.
- To quantify the esterification activity of ACAT in human liver.
Main Methods:
- Incubation of human liver microsomes with CoA, ATP, and radiolabeled oleate or cholesterol.
- Measurement of [14C]cholesteryl oleate formation as an indicator of ACAT activity.
- Comparison of substrate utilization and enzyme activity between human and rat liver preparations.
Main Results:
- Human liver microsomes catalyze the formation of cholesteryl oleate, confirming the presence of cholesterol acyltransferase (ACAT).
- Endogenous cholesterol levels in human microsomes adequately support esterification, similar to rat liver.
- Human liver ACAT shows reduced efficiency in utilizing added cholesterol as a substrate compared to rat liver ACAT.
- The activity of human liver ACAT was found to be 25% of that observed in rat liver under identical assay conditions.
Conclusions:
- Cholesterol acyltransferase (ACAT) is present and active in human liver microsomes.
- Human liver ACAT exhibits distinct substrate preferences, differing from rat liver ACAT.
- The lower specific activity of human liver ACAT suggests potential differences in cholesterol esterification regulation between species.