Cystine is formed by
The difference in structure of cysteine and cystine. Two molecules of cysteine are joined together by S--S bond to form one molecule of cystine. Ref: M.N. Chatterjea - Textbook of Biochemistry, 8th edition, page no: 504
Hydroxylation of cysteine molecule
Carboxylation of cysteine molecule
Peptide bond between two cysteine molecule
Disulfide bond between cysteine molecule
Metabolism of protein and amino acid