| Member | Definition | Role |
|---|
| 2-amino-delta(2)-thiazoline-4-carboxylic acid | A 1,3-thiazole that is 4,5-dihydro-1,3-thiazole which is substituted at positions 2 and 4 by an amino and a carboxy group, respectively. | 2-amino-Delta(2)-thiazoline-4-carboxylic acid zwitterion; 2-amino-Delta(2)-thiazoline-4-carboxylic acid |
| cystathionine ketimine | A 1-thia-4-azacyclohepta-3-ene-3,5-dicarboxylic acid that has R-configuration. It is cyclic sulfur-containing imino acid detected in bovine brain extracts. | cystathionine ketimine |
| cysteine | A sulfur-containing amino acid that is propanoic acid with an amino group at position 2 and a sulfanyl group at position 3. | cysteine zwitterion; cysteine |
| ergothioneine | A L-histidine derivative that is N(alpha),N(alpha),N(alpha)-trimethyl-L-histidine in which the hydrogen at position 2 on the imdazole ring is replaced by a mercapto group. A naturally occurring metabolite of histidine synthesized by bacteria and fungi with antioxidant properties. It is found ubiquitously in plants and animals and is present in many human foodstuffs. | ergothioneine thione form; ergothioneine |
| lanthionine ketimine | A member of the class of 1,4-thiazines that is 3,6-dihydro-2H-1,4-thiazine substituted by carboxy groups at positions 3 and 5. It is a natural but non-proteogenic amino acid found in human urine and brain. | lanthionine ketimine |
| racemethionine | A sulfur-containing amino acid that is butyric acid bearing an amino substituent at position 2 and a methylthio substituent at position 4. | methionine zwitterion; methionine |
| thiazolidine-4-carboxylic acid | A sulfur-containing amino acid that is proline in which the methylene group at position 4 is replaced by a sulfur atom. | thioproline zwitterion; thioproline |