content of endoplasmic reticulum membranes. The data also showed that a modest decrease in SOAT activity led to suppressive effects on Abeta generation. SOAT2 (ACAT2) In a recent study, it was shown that SOAT2 activity is upregulated as a result of chronic renal failure. This study was specific to hepatic SOAT, which plays a major role in hepatic production and release of very low density lipoprotein (VLDL), release of cholesterol, foam cell formation, and atherogenesis. In another study, non-human primates revealed a positive correlation between liver cholesteryl ester secretion rate and the development of coronal artery atherosclerosis. The results of the experiment are indicative that under all of the conditions of cellular cholesterol availability tested, the relative level of SOAT2 expression affects the cholesteryl ester content, and therefore the atherogenecity of nascent apoB-containing lipoproteins. Yeast In yeast, acyl-CoA:sterol acyltransferase (ASAT) is functionally equivalent to ACAT. Although studies in vitro and in yeast suggest that the acyl-CoA binding protein (ACBP) may modulate long-chain fatty acyl-CoA (LCFA-CoA) distribution, the physiological function in mammals is unresolved. Recent research suggests that ACBP expression may play a role in LCFA-CoA metabolism in a physiological context. In S. cerevisiae, the accumulation of ergosteryl esters accompanies entry into the stationary phase and sporulation. Researchers have identified two genes in yeast, ARE2 and ARE1, that encode the different isozymes of ASAT. In yeast, Are2 is the major catalytic isoform. Mitotic cell growth and spore germination are not compromised when these genes are deleted, but diploids that are homozygous for an ARE2 null mutation exhibit a decrease in sporulation efficiency. Plant Synthesis of Steryl Esters In plants cellular sterol ester synthesis is performed by an enzyme different from mammalian ACAT and yeast ASAT; it is performed by Phospholipid:Sterol Acyltransferase (PSAT). A recent study shows that PSAT is involved in the regulation of the pool of free sterols and the amount of free sterol intermediates in the membranes. It is also described as the only intracellular enzyme discovered that catalyzes an acyl-CoA independent sterol ester formation. PSAT is therefore considered to have a similar physiological function in plant cells as ACAT in animal cells. See also ACAT1 mRNA Lecithin—cholesterol acyltransferase (LCAT) References Further reading Figure 2 of the esterification reaction with one molecule of free cholesterol, oleic acid, catalyzed by acyl-CoA: cholesterol acyltransferase. It gives the cholesterol ester cholesterol oleate. from EC 2.3.1 Enzymes of unknown structure