由N6-三甲基赖氨酸合成肉碱和4-N-三甲基氨基丁酸
Biosynthesis of carnitine and 4-N-trimethylaminobutyrate from 6-N-trimethyl-lysine.
作者信息
Cox R A, Hoppel C L
出版信息
Biochem J. 1973 Dec;136(4):1083-90. doi: 10.1042/bj1361083.
The conversion of 6-N-[Me-(14)C]trimethyl-lysine into carnitine and 4-N-trimethylaminobutyrate (butyrobetaine) was demonstrated in rats kept on a lysine-deficient diet. After the rats were given [(14)C]trimethyl-lysine for 4 days, a total of 17% of the injected label was recovered as carnitine from carcass and urine extracts. Another 8% of the trimethyl-lysine label was converted into 4-N-trimethylaminobutyrate, most of which was recovered from the urine. The conversion of trimethyl-lysine into the above two metabolites supports the pathway of carnitine biosynthesis as lysine+methionine --> 6-N-trimethyl-lysine --> 4-N-trimethylaminobutyrate --> carnitine. In addition, three other metabolites representing 2% of the injected dose were recovered. Only an insignificant portion of the label was recovered as free trimethyl-lysine from the carcass, whereas 22% of the injected label was recovered in the urine. A relatively low specific radioactivity in carnitine was found when 5-N-[Me-(14)C]trimethylaminopentanoate and 6-N-[Me-(14)C]trimethylaminohexanoate were administered to rats in amounts similar to the [(14)C]trimethyl-lysine, suggesting that they were not free intermediates.
在赖氨酸缺乏饮食的大鼠中证实了6-N-[甲基-(14)C]三甲基赖氨酸向肉碱和4-N-三甲基氨基丁酸酯（γ-丁甜菜碱）的转化。给大鼠注射[(14)C]三甲基赖氨酸4天后，从 carcass 和尿液提取物中回收的肉碱形式的注射标记物总量为17%。另外8%的三甲基赖氨酸标记物转化为4-N-三甲基氨基丁酸酯，其中大部分从尿液中回收。三甲基赖氨酸向上述两种代谢产物的转化支持了肉碱生物合成途径：赖氨酸+甲硫氨酸→6-N-三甲基赖氨酸→4-N-三甲基氨基丁酸酯→肉碱。此外，还回收了代表注射剂量2%的其他三种代谢产物。从 carcass 中仅回收了少量标记物作为游离三甲基赖氨酸，而在尿液中回收了22%的注射标记物。当以与[(14)C]三甲基赖氨酸相似的量给大鼠施用5-N-[甲基-(14)C]三甲基氨基戊酸酯和6-N-[甲基-(14)C]三甲基氨基己酸酯时，在肉碱中发现相对较低的比放射性，这表明它们不是游离中间体。 （注：原文中“carcass”可能有误，结合语境推测可能是“组织”之类的意思，这里按原文翻译）
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