[sis-teen, -tin]
noun Biochemistry.
a crystalline amino acid, C 6 H 12 O 4 N 2 S 2 , occurring in most proteins, especially the keratins in hair, wool, and horn, and yielding cysteine on reduction.

1835–45; cyst- + -ine2; so called because found in the bladder Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2014.
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World English Dictionary
cystine (ˈsɪstiːn, -tɪn)
a sulphur-containing amino acid present in proteins: yields two molecules of cysteine on reduction. Formula: HOOCCH(NH2)CH2SSCH2CH(NH2)COOH
[C19: see cysto- (bladder), -ine²; named from its being discovered in a type of urinary calculus]

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American Heritage
Medical Dictionary

cystine cys·tine (sĭs'tēn')
A white crystalline amino acid that is found in many proteins, especially keratin, and is the major source of metabolic sulfur.

The American Heritage® Stedman's Medical Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
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Encyclopedia Britannica


a crystalline, sulfur-containing amino acid that is formed from two molecules of the amino acid cysteine. Cystine can be converted to cysteine by reduction (in this case, the addition of hydrogen). Discovered in 1810, cystine was not recognized as a component of proteins until 1899, when it was isolated from animal horn. Cystine is particularly abundant in skeletal and connective tissues and in hair, horn, and wool.

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Encyclopedia Britannica, 2008. Encyclopedia Britannica Online.
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