Acyl-coenzyme A: cholesterol acyltransferase. Transfer of cholesterol to its substrate pool and modulation of activity
| Autor: | K.A. Mitropoulos, Stella Synouri-Vrettakou |
|---|---|
| Rok vydání: | 1983 |
| Předmět: |
Male
Sterol O-acyltransferase In Vitro Techniques Biochemistry chemistry.chemical_compound Animals Phospholipids chemistry.chemical_classification Liposome Cholesterol Vesicle Reverse cholesterol transport Temperature Substrate (chemistry) Rats Inbred Strains Rats Enzyme Activation Enzyme chemistry Liposomes Microsome Microsomes Liver lipids (amino acids peptides and proteins) Acyl Coenzyme A Acyltransferases Sterol O-Acyltransferase |
| Zdroj: | European journal of biochemistry. 133(2) |
| ISSN: | 0014-2956 |
| Popis: | The preincubation at 37°C of rat liver microsomal fraction, followed by re-isolation of the treated vesicles, results in a time-dependent increase in the activity of acyl-CoA: cholesterol acyltransferase. The presence of cholesterol-phospholipid (1:1, mol/mol) liposomes results in higher rate of increase in activity and under these conditions the rate of increase is liposomal cholesterol concentration-dependent. The preincubation of the microsomal fraction in the presence of [3H]cholesterol-phospholipid liposomes results in transfer of [3H]cholesterol to the re-isolated microsomal vesicles and this transfer follows first-order kinetics in respect to the donor concentration. These preincubations result also in a time-dependent and liposomal cholesterol concentration-dependent increase in the incorporation of [3H]cholesterol into the cholesteryl oleate produced on assay of cholesterol acyltransferase activity. From specific radioactivity data of the cholesteryl esters synthesised on assay of cholesterol acyltransferase in treated microsomal preparations, the rate of liposomal [3H]cholesterol equilibration with the cholesterol acyltransferase substrate pool can be calculated. The half-time of this transfer decreased with the concentration of liposomal cholesterol present during the preincubation. The activation energy for the transfer of liposomal cholesterol to the cholesterol acyltranferase substrate pool was 87.9 kJ/mol and was independent of the concentration of liposomal cholesterol. The activation energy for the rate of increase of total cholesteryl oleate was similar to this value for low concentrations of liposomal cholesterol and progressively decreased with increasing concentrations of liposomal cholesterol. The liposomal cholesterol and progressively decreased with increasing concentrations of liposomal cholesterol. The data suggest that under the present conditions, the time-dependent and temperature-dependent increase in cholesterol acyltransferase activity is due to the transfer of non-esterified cholesterol from other microsomal and/or liposomal vesicles to the vesicles that contain the enzyme and therefore to increased availability of substrate. |
| Databáze: | OpenAIRE |
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