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Tryptophan and cysteine

Analysis of Tryptophan, Cysteine and Cystine amino acids

Separate individual analysis must be formed for the accurate determination of tryptophan, cysteine and cystine amino acids. Without pre-treatment or special analysis, the recovery of these amino acids is affected or lost altogether.

Tryptophan is destroyed during conventional acid hydrolysis, but is stable to alkaline hydrolysis with barium hydroxide. We are able to provide a separate alkaline system that will ensure the tryptophan is not destroyed and can be quantified.

Cystine and cysteine are also unstable to conventional acid hydrolysis, but oxidation to cysteic acid using performic acid prior to acid hydrolysis gives very good recovery and accurate quantification of Cys. As the recovery of other amino acids in the sample may be affected by this pre-treatment, we must run this type of analysis in addition to our standard hydrolysis run.

To summarise, both these methods adversely affect recovery of the other amino acids, therefore in order to quantify all 20 amino acids three completely separate analyses are required: acid hydrolysis, alkaline hydrolysis, and acid hydrolysis with performic acid oxidation.

We can, if the peptide sequence is known, estimate the values but for accurate determination, we need to perform separate analyses as detailed above.

For information on testing any products for tryptophan or cysteine content, please request a quotation or email us at or call us on +44(0)1527 584495 to speak to one of our experts.