- Main Entry:
- me·thi·o·nine

- Pronunciation:
-
\mə-ˈthī-ə-ˌnēn\
- Function:
- noun
- Etymology:
- International Scientific Vocabulary, from methyl + thion- + 2-ine
- Date:
- 1928
: a crystalline sulfur-containing essential amino acid C5H11NO2S that occurs in the levorotatory form as a constituent of many proteins