Cystine is formed by: (A) Hydroxylation of cysteine molecule, (B) Carboxylation of cysteine molecule, (C) Peptide bond between two cysteine molecule, (D) Disulfide bond between cysteine molecule
Answer is D. 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