title: Phospholipid fatty acid modification of rat liver microsomes affects acylcoenzyme A:cholesterol acyltransferase activity.
abstract: The effect of phospholipid fatty acyl composition on the activity of acylcoenzyme A:cholesterol acyltransferase was investigated in rat liver microsomes. Specific phosphatidylcholine replacements were produced by incubating the microsomes with liposomes and bovine liver phospholipid-exchange protein. Although the fatty acid composition of the microsomes was modified appreciably, there was no change in the microsomal phospholipid or cholesterol content. As compared to microsomes enriched for 2 h with dioleoylphosphatidylcholine, those enriched with dipalmitoylphosphatidylcholine exhibited 30-45% less acyl-CoA:cholesterol acyltransferase activity. Enrichment with 1-palmitoyl-2-linoleoylphosphatidylcholine increased acyl-CoA:cholesterol acyltransferase activity by 20%. By contrast, dilinoleoylphosphatidylcholine abolished microsomal acyl-CoA:cholesterol acyltransferase activity almost completely. Addition of cofactors that stimulated microsomal lipid peroxidation inhibited acyl-CoA:cholesterol acyltransferase activity by only 10%, however, and did not increase the inhibition produced by submaximal amounts of dilinoleoylphosphatidylcholine. Certain of the phosphatidylcholine replacements produced changes in palmitoyl-CoA hydrolase, NADPH-dependent lipid peroxidase, glucose-6-phosphatase and UDPglucuronyl transferase activities, but they did not closely correlate with the alterations in acyl-CoA:cholesterol acyltransferase activity. Electron spin resonance measurements with the 5-nitroxystearate probe indicated that microsomal lipid ordering was reduced to a roughly similar extent by dioleoyl- or by dilinoleoylphosphatidylcholine enrichment. Since these enrichments produce widely different effects on acyl-CoA:cholesterol acyltransferase activity, changes in bulk membrane lipid fluidity cannot be the only factor responsible for phospholipid fatty acid compositional effect on acyl-CoA:cholesterol acyltransferase. The present results are more consistent with a modulation resulting from either changes in the lipid microenvironment of acyl-CoA:cholesterol acyltransferase or a direct interaction between specific phosphatidylcholine fatty acyl groups and acyl-CoA:cholesterol acyltransferase.
mesh_terms: D000214:Acyl Coenzyme A / Q000378:metabolism*; D000217:Acyltransferases / Q000378:metabolism*; D000818:Animals; D002784:Cholesterol / Q000378:metabolism; D004578:Electron Spin Resonance Spectroscopy; D005227:Fatty Acids / Q000378:metabolism*; D008081:Liposomes / Q000378:metabolism; D008563:Membrane Lipids / Q000378:metabolism; D008862:Microsomes, Liver / Q000201:enzymology*; D010743:Phospholipids / Q000378:metabolism*; D051381:Rats; D002785:Sterol O-Acyltransferase / Q000378:metabolism*
chemical_list: D000214:Acyl Coenzyme A; D005227:Fatty Acids; D008081:Liposomes; D008563:Membrane Lipids; D010743:Phospholipids; D002784:Cholesterol; D000217:Acyltransferases; D002785:Sterol O-Acyltransferase