Augmentation of cholesterol esterification in the microsomal membrane by the removal of membrane-bound ribosomes.
Acyl-CoA: cholesterol O-acyltransferase (ACAT) activity in rough microsomes was enhanced (2-fold) by the removal (40%) of ribosomes from the microsomal membrane with RNase. Although EDTA was as efficient as RNase in the removal of ribosomes the stimulation (3.2-fold) of ACAT activity was even more, suggesting that additional effects were induced by EDTA. Reconstitution of EDTA-treated microsomes with ribosomes decreased the cholesterol-esterifying activity (40%) of the degranulated microsomes. Alternate possibilities were considered for the enhancement of ACAT activity by EDTA, namely, suppression of the hydrolysis of added palmitoyl-CoA substrate, the hydrolysis of cholesteryl ester, and the removal of metal suppressor of ACAT activity. Neither acyl-CoA hydrolase nor cholesteryl ester hydrolase activity was decreased after degranulation of microsomes. ACAT activity of EDTA-treated microsomes compared to the control was enhanced rather than suppressed after the addition of Ca2+, Mg2+, and Ba2+ ions whereas other metal ions (Co2+, Cu2+, Zn2+) almost completely suppressed ACAT activity in both the EDTA-treated and buffer-treated microsomes. It is concluded that the enhanced ACAT activity was largely due to the removal of ribosomes from the microsomal membrane.
D000818:Animals; D002458:Cell Fractionation; D002788:Cholesterol Esters / Q000378:metabolism*; D004492:Edetic Acid / Q000494:pharmacology; D008297:Male; D008854:Microscopy, Electron; D008862:Microsomes, Liver / Q000201:enzymology*; D051381:Rats; D011919:Rats, Inbred Strains; D012260:Ribonucleases / Q000378:metabolism; D012270:Ribosomes / Q000502:physiology*; D002785:Sterol O-Acyltransferase / Q000378:metabolism*
D002788:Cholesterol Esters; D004492:Edetic Acid; D002785:Sterol O-Acyltransferase; D012260:Ribonucleases