Henderson L M, Nelson P J, Henderson L
Fed Proc. 1982 Oct;41(12):2843-7.
The biosynthesis of carnitine proceeds from trimethyllysine (TML) by beta-hydroxylation by a liver or kidney mitochondrial enzyme, which requires oxygen, alpha-ketoglutarate, ferrous iron, and ascorbate. This dioxygenase is rapidly inactivated by preincubation with Fe2+, but not Fe3+. The evidence suggests that superoxide anion is involved in the hydroxylation. beta-Hydroxytrimethyllysine undergoes aldol cleavage to glycine and trimethylaminobutyraldehyde under the influence of serine hydroxymethyltransferase and possibly a specific aldolase. The next step, the aldehyde oxidation, is catalyzed by a specific NAD-dependent aldehyde dehydrogenase from liver cytosol. The product, trimethylaminobutyrate, is then hydroxylated by a cytosolic dioxygenase to carnitine. This enzyme, which has the same cofactor requirements as TML hydroxylase, is found in the liver of all species examined, but is absent from the kidney of some species.
肉碱的生物合成从三甲基赖氨酸（TML）开始，由肝脏或肾脏线粒体酶进行β-羟基化反应，该反应需要氧气、α-酮戊二酸、亚铁离子和抗坏血酸。这种双加氧酶在与Fe2+预孵育后会迅速失活，但与Fe3+预孵育则不会。有证据表明超氧阴离子参与了羟基化反应。在丝氨酸羟甲基转移酶以及可能还有一种特定醛缩酶的作用下，β-羟基三甲基赖氨酸发生醛醇裂解生成甘氨酸和三甲基氨基丁醛。下一步，醛的氧化由肝脏胞质溶胶中一种特定的依赖NAD的醛脱氢酶催化。产物三甲基氨基丁酸随后被一种胞质双加氧酶羟基化为肉碱。这种酶与TML羟化酶具有相同的辅助因子需求，在所检测的所有物种的肝脏中都能找到，但在某些物种的肾脏中不存在。
