derives from L-cystine (cross-link) oxidized residue oxidation of disulfide crosslink in cystine to two cysteic acids 301.98785400390625 302.290008544921875 97.985137939453125 98.01000213623046875 C 6 H 10 N 2 O 8 S 2 H 2 O 6 PSI-MOD artifact A protein modification that effectively oxidizes the disulfide bond of a cystine crosslink to form two cysteic acid residues. Cross-link 2. This modification destroys a cross-link. From DeltaMass: Average Mass: 98 Abbreviation: Cya Average Mass Change: 98 Notes: Treatment of cystine by strongly oxidising reagents such as performic acid results in the breakage of the disulphide bond and complete oxidation of the sulphur atoms on each molecule. Such treatment is often carried out prior to amino acid analysis as the resulting cysteic acid is then resistant to acid degradation during the hydrolysis procedure. MOD:00034 none MOD:01012