Adeva-Andany María M, Calvo-Castro Isabel, Fernández-Fernández Carlos, Donapetry-García Cristóbal, Pedre-Piñeiro Ana María
Hospital Juan Cardona, Rúa Pardo Bazán, Ferrol, Spain.
IUBMB Life. 2017 Aug;69(8):578-594. doi: 10.1002/iub.1646. Epub 2017 Jun 26.
Carnitine acyltransferases catalyze the reversible transfer of acyl groups from acyl-coenzyme A esters to l-carnitine, forming acyl-carnitine esters that may be transported across cell membranes. l-Carnitine is a wáter-soluble compound that humans may obtain both by food ingestion and endogenous synthesis from trimethyl-lysine. Most l-carnitine is intracellular, being present predominantly in liver, skeletal muscle, heart and kidney. The organic cation transporter-2 facilitates l-carnitine uptake inside cells. Congenital dysfunction of this transporter causes primary l-carnitine deficiency. Carnitine acetyltransferase is involved in the export of excess acetyl groups from the mitochondria and in acetylation reactions that regulate gene transcription and enzyme activity. Carnitine octanoyltransferase is a peroxysomal enzyme required for the complete oxidation of very long-chain fatty acids and phytanic acid, a branched-chain fatty acid. Carnitine palmitoyltransferase-1 is a transmembrane protein located on the outer mitochondrial membrane where it catalyzes the conversion of acyl-coenzyme A esters to acyl-carnitine esters. Carnitine acyl-carnitine translocase transports acyl-carnitine esters across the inner mitochondrial membrane in exchange for free l-carnitine that exits the mitochondrial matrix. Carnitine palmitoyltransferase-2 is anchored on the matrix side of the inner mitochondrial membrane, where it converts acyl-carnitine esters back to acyl-coenzyme A esters, which may be used in metabolic pathways, such as mitochondrial β-oxidation. l-Carnitine enhances nonoxidative glucose disposal under euglycemic hyperinsulinemic conditions in both healthy individuals and patients with type 2 diabetes, suggesting that l-carnitine strengthens insulin effect on glycogen storage. The plasma level of acyl-carnitine esters, primarily acetyl-carnitine, increases during diabetic ketoacidosis, fasting, and physical activity, particularly high-intensity exercise. Plasma concentration of free l-carnitine decreases simultaneously under these conditions. © 2017 IUBMB Life, 69(8):578-594, 2017.
肉碱酰基转移酶催化酰基从酰基辅酶A酯可逆地转移至左旋肉碱，形成可穿过细胞膜的酰基肉碱酯。左旋肉碱是一种水溶性化合物，人类可通过食物摄入以及由三甲基赖氨酸进行内源性合成来获取。大多数左旋肉碱存在于细胞内，主要分布在肝脏、骨骼肌、心脏和肾脏中。有机阳离子转运体2促进左旋肉碱进入细胞。该转运体的先天性功能障碍会导致原发性左旋肉碱缺乏症。肉碱乙酰转移酶参与线粒体中过量乙酰基的输出以及调节基因转录和酶活性的乙酰化反应。肉碱辛酰转移酶是超长链脂肪酸和植烷酸（一种支链脂肪酸）完全氧化所需的过氧化物酶体酶。肉碱棕榈酰转移酶1是一种位于线粒体外膜的跨膜蛋白，在那里它催化酰基辅酶A酯转化为酰基肉碱酯。肉碱/酰基肉碱转位酶将酰基肉碱酯转运穿过线粒体内膜，以交换离开线粒体基质的游离左旋肉碱。肉碱棕榈酰转移酶2锚定在线粒体内膜的基质侧，在那里它将酰基肉碱酯转化回酰基辅酶A酯，后者可用于代谢途径，如线粒体β氧化。在正常血糖高胰岛素血症条件下，左旋肉碱可增强健康个体和2型糖尿病患者的非氧化葡萄糖代谢，这表明左旋肉碱可增强胰岛素对糖原储存的作用。在糖尿病酮症酸中毒、禁食和体育活动（尤其是高强度运动）期间，酰基肉碱酯（主要是乙酰肉碱）的血浆水平会升高。在这些情况下，游离左旋肉碱的血浆浓度会同时降低。© 2017国际生物化学与分子生物学联盟生命科学，69(8):578 - 594，2017。
