Cystine

Cystine is the tertiary structure of most proteins. Disulfide bonding, along with hydrogen bonding and hydrophobic interactions is partially responsible for the formation of the gluten matrix in bread. Human hair contains approximately 5% cystine by mass.^[2]

Properties

The disulfide link is readily reduced to give the corresponding thiol, cysteine. This reaction is typically effected with thiols such as dithiothreitol.

(SCH₂CH(NH₂)CO₂H)₂ + 2 RSH → 2 HSCH₂CH(NH₂)CO₂H + RSSR

Nutritional sources

Supplemental N-acetyl cysteine is claimed to be a source of cystine, but the dose of this supplement is limited by side effects. One of the richest nutritional sources of cystine in the diet is glutathione can be synthesized.

In animal feed

Disulfide bonds can be broken at temperatures above about 150 °C, especially at low moisture levels (below about 20%)^[3].

Side effects

Nutritional sources of cystine are virtually free of the toxic side effects associated with the single molecule of cysteine, N-acetyl cysteine. The greatest dietary source of cystine is bio-active, unpasteurized or low-heat pasteurized undenatured whey proteins.^{[citation needed]}

See also

• Cystinuria
• Cysteine

References

1. ^ "cystine." Encyclopædia Britannica. 2007. Encyclopædia Britannica Online. 27 July 2007 www.britannica.com/eb/article-9028437/cystine
2. ^ Gortner, R. A.; W. F. Hoffman, W. F. (1941). "l-Cystine". Org. Synth.; Coll. Vol. 1: 194. 
3. ^ M.A. Aslaksena, O.H. Romarheima, T. Storebakkena and A. Skrede (28 June 2006). "Evaluation of content and digestibility of disulfide bonds and free thiols in unextruded and extruded diets containing fish meal and soybean protein sources". Animal Feed Science and Technology 128 (3-4): 320-330.