Tryptophan ninhydrin reaction

Also Tojo and Uenoyama (T2) by means of paper chromatography detected neither 5-hydroxyanthranilic acid nor its conjugate forms in urine of senile cataract patients. They found, however, an ethanol-extractable substance giving a positive ninhydrin reaction and Rf value coinciding with that of tryptophan. The oral administration of a dose of anthra-nilic acid did not alter their findings. 

Zahnley and Davis 456) found that colorimetric determination of tryptophan in intact proteins by the ninhydrin reaction gives high apparent tryptophan contents for proteins having high tyrosine/tryp-tophan ratios. An equation was proposed to correct for this interference by tyrosine. To apply the correction, the tyrosine content must be known, but it can be determined readily by other methods. Application of such a correction to chicken ovoinhibitor, which contains 17 tyrosine residues and one tryptophan residue per molecule, gave results that agree with the tryptophan content determined by other methods such as fluorescence, oxidation with NBS and magnetic circular dichroism. 

The analysis of amino acids involves chromatographic issues similar to those encountered in analysis of simple amines. Underivatized amino acids have, with a few exceptions, weak UV absorbance and a strong tendency to interact with stationary phases in undesirable ways. Underivatized amino acids are normally separated with ion exchange chromatography, then visualized post-column by reaction with ninhydrin, o-phthaladehyde (OPA), or other agents. Underivatized tryptophan and the metabolites kynurenine, 3-hydroxykynurenine, kynurenic acid, and 3-hydroxyanthranilic acid, were separated on a Partisphere 5-p ODS column with fluorescent detection.121... 

Steiner et al. (1998) used HPTLC to analyze amino acids in water conditioned by several medically important snails—Biomphalaria glabrata, Helisoma trivolvis, and Lymnaea elodes. Snail-conditioned water (SCW) provides information value (in the form of pheromones) to attract larval trematode parasites. The SCW samples were dried with air and reconstituted in 10% -propanol and then applied to cellulose HPTLC plates and developed with n-propanol-water (7 3). Amino acids were detected with ninhydrin reagent and the resulting color sample zones were compared to known standards. The amino acids present in SCW (h/ p values and color reactions with ninhydrin given in parentheses) were as follows an unknown (7, purple), aspartic acid (21, purple), serine (29, purple), alanine (40, purple), tryptophan (51, purple), valine (58, purple/orange), phenylalanine (64, light blue), and leucine (69, purple). The above amino acids were detected in the SCW of all the snails, except that phenylalanine was not detected in Lymnaea elodes. 

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