肌氨酸(英语：sarcosine)即N-甲基甘氨酸，或2-甲氨基乙酸，非编码氨基酸。可以由氯乙酸与甲胺反应制得。它是胆碱自然代谢为甘氨酸过程中的一个中间体。肌氨酸有甜味，溶于水。

Sarcosine, also known as N-methylglycine, is an intermediate and byproduct in glycine synthesis and degradation. Sarcosine is metabolized to glycine by the enzyme sarcosine dehydrogenase, while glycine-N-methyl transferase generates sarcosine from glycine. Sarcosine is a natural amino acid found in muscles and other body tissues. In the laboratory, it may be synthesized from chloroacetic acid and methylamine. Sarcosine is found naturally as an intermediate in the metabolism of choline to glycine. Sarcosine is sweet to the taste and dissolves in water. It is used in manufacturing biodegradable surfactants and toothpastes as well as in other applications.