Therefore, methionine, cysteine and cystine are the principle sources of sulphur in the body.
Cystine, cysteine and methionine are source of a part of the structure of insulin and the keratin of hair and are involved with oxidation-reduction reactions in the body.
While protein eaten in excess of that required for growth or cellular repair may be utilized as a source of energy, it is not considered that they are efficiently utilized for this purpose.
Cystine is a dimer of cysteine, in which the two cysteine residues are connected via disulfide bond. This due to cysteine is unstable in solution and readily oxidized to the dimer form.
Methionine is an essential amino acid and has to be supplied in the diet. Cysteine is not essential can be synthesized in the body from methionine. The presence of cysteine and cystine in the diet reduces the requirement of methionine.
Amino acid of cystine, cysteine and methionine
