Amino acid analysis is a method to determine the absolute amounts of individual amino acids in a sample. The method can be applied to samples containing free amino acids. However it may also be used on peptides and protein samples after hydrolysis into amino acids.
Amino acid analysis can be used for determination of the relative composition of amino acids in a protein. It can also be used for determination of the absolute amount of a protein or peptide if the amino acid sequence is known. Finally, it is used for purity estimation of a purified protein.
In amino acid analysis it should be noted that:
- Serine and threonine are degraded slightly during acid hydrolysis, and recoveries can be 10% lower than expected.
- Methionine can be oxidized during hydrolysis, usually less than 10% is oxidized.
- Valine and isoleucine bonds (Val-Val, Ile-Val, Val-Ile, Ile-Ile) are difficult to hydrolyse and recoveries can be 5-15% lower than expected.
- Glycine content is often higher than expected because it is a frequent contaminant due to its use in many buffers. Analysis of known amounts of amino acids standards is used to determine a compensation factor to correct for differences in ninhydrin reactivity.
Read more about Quantitative Amino Acid Analysis on the Alphalyse website