Recent studies have suggested that parts of the hepatic activities of diacylglycerol acyltransferase and acyl choles-terol acyltransferase are expressed in the lumen of the endoplasmic reticulum (ER). However the ER membrane is impermeable to the long-chain fatty acyl-CoA substrates of these enzymes. Livermicrosomal vesicles thatwere shown to be at least 95%impermeable topalmitoyl-CoAwere used to demonstrate the membrane transport of palmitoylcarnitine and freeL-carnitine – processes that are necessary for an indirect route of provision of ER luminal fatty acyl-CoA through a luminal carnitine acyltransferase (CAT). .
