Analysis of Tryptophan, Cysteine and Cystine amino acids
Tryptophan and cysteine are generally found in proteins and may also be incorporated in peptides. For the analysis of these specific amino acids in samples, AltaBioscience uses different methods that enable us to quantify both Cys and Trp accurately.
Separate individual analyses must be performed 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.
During standard analysis, Tryptophan is destroyed using 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 accurately quantified.
Cysteine is also unstable to conventional acid hydrolysis. It is usually observed as cystine, and its recovery is variable using standard hydrolysis conditions. However, 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 the 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 for Cys and Trp, but for accurate determination, we need to perform separate analyses as detailed above.