The Chemical Entities of Biological Interest (ChEBI) ontology is downloaded weekly from EMBL-EBI at http://www.ebi.ac.uk/chebi/. The data is made available under the Creative Commons License (CC BY 3.0, http://creativecommons.org/licenses/by/3.0/). For more information see: Degtyarenko et al. (2008) ChEBI: a database and ontology for chemical entities of biological interest. Nucleic Acids Res. 36, D344–D350.
An L-cysteine thioether that is L-cysteine in which the hydrogen of the thiol group has been replaced by a 1,2-dicarboxyethyl group. It is a chemical modification which occurs in tissue proteins and formed by a Michael addition of cysteine to fumaric acid.