Brady P S, Ramsay R R, Brady L J
Department of Food Science and Nutrition, University of Minnesota, St. Paul 55108.
FASEB J. 1993 Aug;7(11):1039-44. doi: 10.1096/fasebj.7.11.8370473.
Long-chain carnitine acyltransferases are a family of enzymes found in mitochondria, peroxisomes, and endoplasmic reticulum that catalyze the exchange of carnitine for coenzyme A in the fatty acyl-CoA. Conversion of the fatty acyl-CoA to fatty acylcarnitine renders the fatty acid more permeable to the various cellular membranes. The mitochondrial carnitine palmitoyltransferases are considered important in the regulation of mitochondrial beta-oxidation of long-chain fatty acids. However, palmitoylcarnitine produced by peroxisomal carnitine octanoyltransferase or by microsomal carnitine palmitoyltransferase is not different from that produced by the mitochondrial enzyme. Therefore, for there to be control of fatty acid oxidation by the long-chain carnitine acyltransferases, there would have to be some mechanism to coordinately regulate these varied enzymes. The first system of regulation involves inhibition by malonyl-CoA, an intermediate in the synthesis of fatty acids. Malonyl-CoA inhibits long-chain carnitine acyltransferase activity by all three enzymes at similar concentrations in the physiological range. In addition, the mitochondrial and peroxisomal enzymes are known to be regulated at the level of mRNA transcription by a number of shared factors. Although the microsomal enzyme is less well studied, there does, indeed, appear to be a pattern of coordinate regulation for this system.
长链肉碱酰基转移酶是一类存在于线粒体、过氧化物酶体和内质网中的酶，它们催化肉碱与脂肪酸辅酶A中的辅酶A进行交换。脂肪酸辅酶A转化为脂肪酰肉碱后，脂肪酸对各种细胞膜的通透性更高。线粒体肉碱棕榈酰转移酶被认为在长链脂肪酸的线粒体β氧化调节中起重要作用。然而，过氧化物酶体肉碱辛酰转移酶或微粒体肉碱棕榈酰转移酶产生的棕榈酰肉碱与线粒体酶产生的并无不同。因此，要通过长链肉碱酰基转移酶来控制脂肪酸氧化，就必须有某种机制来协调调节这些不同的酶。第一种调节系统涉及丙二酰辅酶A的抑制作用，丙二酰辅酶A是脂肪酸合成的中间产物。在生理范围内，丙二酰辅酶A以相似的浓度抑制这三种酶的长链肉碱酰基转移酶活性。此外，已知线粒体和过氧化物酶体酶在mRNA转录水平受到多种共同因子的调节。虽然微粒体酶的研究较少，但这个系统确实似乎存在一种协调调节模式。
