Ethionine

Ethionine is a non-proteinogenic amino acid structurally related to methionine, with an ethyl group in place of the methyl group.

Ethionine is an antimetabolite and methionine antagonist. It prevents amino acid incorporation into proteins and interferes with cellular use of adenosine triphosphate (ATP). Because of these pharmacological effects, ethionine is highly toxic and is a potent carcinogen.