Editing Cystine (section)

===Redox===
It is formed from the oxidation of two cysteine molecules, which results in the formation of a [[disulfide bond]]. In cell biology, cystine residues (found in proteins) only exist in non-reductive (oxidative) organelles, such as the secretory pathway ([[endoplasmic reticulum]], [[Golgi apparatus]], [[lysosome]]s, and vesicles) and extracellular spaces (e.g., [[extracellular matrix]]). Under reductive conditions (in the cytoplasm, nucleus, etc.) cysteine is predominant. The disulfide link is readily reduced to give the corresponding [[thiol]] [[cysteine]]. Typical thiols for this reaction are [[mercaptoethanol]] and [[dithiothreitol]]:
:(SCH<sub>2</sub>CH(NH<sub>2</sub>)CO<sub>2</sub>H)<sub>2</sub>  +  2 RSH  →  2 HSCH<sub>2</sub>CH(NH<sub>2</sub>)CO<sub>2</sub>H  +  RSSR
Because of the facility of the thiol-disulfide exchange, the nutritional benefits and sources of cystine are identical to those for the more-common [[cysteine]]. Disulfide bonds cleave more rapidly at higher temperatures.<ref>{{cite journal
|author1=Aslaksena, M.A. |author2=Romarheima, O.H. |author3=Storebakkena, T. |author4=Skrede, A. | title = Evaluation of content and digestibility of disulfide bonds and free thiols in unextruded and extruded diets containing fish meal and soybean protein sources
| journal = Animal Feed Science and Technology
| volume = 128
| issue = 3–4
| pages = 320–330
| date = 28 June 2006
| doi = 10.1016/j.anifeedsci.2005.11.008 }}</ref>