Reaction of ninhydrin in acid solution with straight-chain amino acids containing two amino groups and its application to the estimation of α∈-diaminopimelic acid

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Abstract
At pH 1 or less ninhydrin reacts with straight-chain aa-diaminodicarboxylic acids, including sulfur-containing compounds, and with dibasic amino acids. The spectra of the reaction products, ex-cept that with diaminoadipic acid, all show absorption peaks at 320-350 m[mu] and sometimes also at 430-460 m[mu]. Diaminoadipic acid resembles ornithine in having its main peak at 515 m[mu]. Change in acidity affects the shape of the absorption spectrum of diaminopimelic acid only. The ab-sorption at 440 m[mu] increases on decrease of pH from 1.0 to 0.3. The reaction can be used for the estimation of diaminopimelic acid, pro-vided that tryptophan, cystine, ornithine, proline and lysine are not present in excess.