Kerkhoff C, Beuck M, Threige-Rasmussen J, Spener F, Knudsen J, Schmitz G
Institut fur Klinische Chemie und Laboratoriumsmedizin, Klinikum der Universitat Regensburg, Germany.
Biochim Biophys Acta. 1997 Jun 2;1346(2):163-72. doi: 10.1016/s0005-2760(97)00030-1.
It is demonstrated that the acyl-CoA:cholesterol acyltransferase (ACAT) enzyme activity in rough endoplasmatic reticulum membranes is regulated by the acyl-CoA binding protein (ACBP). The ACAT activity is strongly inhibited by different ACBP/oleoyl-CoA complexes depending from the molar ratio of protein and fatty acid-CoA. Other lipid binding proteins such as bovine serum albumin and the liver fatty acid binding protein do not show any effects on ACAT activity. In addition, we can show that cholesterol loading with acetylated low density lipoproteins does not lead to an increase of the ACBP mRNA level. Consequently, the increase of the intracellular concentration of fatty acids because of the cholesteryl ester accumulation renders ACAT more active for cholesterol esterification. In binding studies we have characterized binding sites on microsomal membranes for the ACAT substrate oleoyl-CoA and the ACAT inhibitor diazepam. Diazepam competes with oleoyl-CoA and vice versa for its binding to microsomal membranes. This common binding site is suggested to be responsible for the transfer from ACBP-bound oleoyl-CoA to ACAT and, therefore, to be essential for the microsomal cholesterol esterification.
结果表明，糙面内质网膜中的酰基辅酶A：胆固醇酰基转移酶（ACAT）的酶活性受酰基辅酶A结合蛋白（ACBP）调控。不同的ACBP/油酰辅酶A复合物会根据蛋白质与脂肪酸辅酶A的摩尔比强烈抑制ACAT活性。其他脂质结合蛋白，如牛血清白蛋白和肝脏脂肪酸结合蛋白，对ACAT活性没有任何影响。此外，我们可以证明，用乙酰化低密度脂蛋白进行胆固醇加载不会导致ACBP mRNA水平升高。因此，由于胆固醇酯积累导致细胞内脂肪酸浓度增加，使得ACAT在胆固醇酯化方面更具活性。在结合研究中，我们对微粒体膜上ACAT底物油酰辅酶A和ACAT抑制剂地西泮的结合位点进行了表征。地西泮与油酰辅酶A竞争与其结合到微粒体膜上，反之亦然。这个共同的结合位点被认为负责将ACBP结合的油酰辅酶A转移到ACAT，因此，对微粒体胆固醇酯化至关重要。
