Molecular aspects of the in vivo and in vitro effects of ethionine, an analog of methionine

Ethionine is the S-ethyl analog of the essential amino acid methionine. This substitution appreciably increases molecular bulk and length. It is debatable whether or not ethionine occurs naturally, although the latter is more likely. Presumably, ethionine blocks one or more of the essential functions of methionine in cells, because most of its biochemical and morphological effects are reversed by the administration of methionine or adenine (this fact alone makes it unique when compared with other carcinogens). Any of the following processes could be affected: the biosynthesis of proteins, ribonucleic acid (RNA), deoxyribonucleic acid (DNA), and phospholipids or transmethylation reactions in which methionine is the methyl donor (e.g. the synthesis of choline). Each of these possibilities has been investigated.