[sis-teen, -tin]
noun Biochemistry.
  1. a crystalline amino acid, C6H12O4N2S2, occurring in most proteins, especially the keratins in hair, wool, and horn, and yielding cysteine on reduction.

Origin of cystine

1835–45; cyst- + -ine2; so called because found in the bladder Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

Examples from the Web for cystine

Historical Examples of cystine

  • Ammonia, therefore, dissolves the cystine without entering into chemical union with it.

  • This action is due chiefly to its progressive formation of calcium sulphydrate from the cystine group of the softer keratins.

    Animal Proteins

    Hugh Garner Bennett

British Dictionary definitions for cystine


  1. a sulphur-containing amino acid present in proteins: yields two molecules of cysteine on reduction. Formula: HOOCCH(NH 2)CH 2 SSCH 2 CH(NH 2)COOH

Word Origin for cystine

C19: see cysto- (bladder), -ine ²; named from its being discovered in a type of urinary calculus
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

cystine in Medicine


  1. 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.