Encyclopedia of Astrobiology

Living Edition
| Editors: Muriel Gargaud, William M. Irvine, Ricardo Amils, Henderson James Cleaves, Daniele Pinti, José Cernicharo Quintanilla, Michel Viso


  • Kensei Kobayashi
Living reference work entry
DOI: https://doi.org/10.1007/978-3-642-27833-4_383-4


Cystine (Fig. 1) is formed by the oxidative condensation of two cysteine molecules. Cysteine, one of the 20 protein amino acids, has a thiol (─SH) group. In aqueous solution, two thiol groups readily oxidize to form a disulfide bond (─S─S─). Thus, cystine rather than cysteine is usually determined when the amino acid composition of protein hydrolysates is analyzed. It can be easily reduced to give two cysteine molecules. In protein molecules, cysteine residues make intramolecular disulfide bonds, which stabilize protein tertiary structure.


Aqueous Solution Acid Composition Bioorganic Chemistry Disulfide Bond Cysteine Residue 
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© Springer-Verlag Berlin Heidelberg 2014

Authors and Affiliations

  1. 1.Yokohama National UniversityYokohamaJapan