Abstract
In the proposed method, the mixture of amino-acids resulting from the hydrolysis of a protein is first separated into groups as described by Fromageot, Jutisz, and Lederer, after isolation from the other amino-acids the dicarboxylic acids are converted by nitrous acid into hydroxyacids and the latter are oxidized by permanganic acid; under these conditions, only aspartic acid produces acetaldehyde which is determined quantitatively by p-hydroxydiphenyl or by nitroprussiate. The amount of glutamic acid is calculated from the difference between the total nitrogen content of the eluted fraction and the nitrogen content of the aspartic acid. This method allows the determination of aspartic acid in amounts between 0.015 and 2.0 mg with a maximum error of 5%. The following results were obtained with different proteins: gelatin: aspartic acid 3.1 glutamic acid 12.0%; globin (rabbit): aspartic acid 4.2, glutamic acid 1.5%; insuline: aspartic acid 5.3, glutamic acid 19.3; lysozyme: aspartic acid 10.2; edestin: aspartic acid 10.5, glutamic acid 16.9; zein: aspartic acid 3.5, glutamic acid 34.8. This method cannot be used for the determination of glutamic acid in proteins rich in tryptophan such as lysozyme.
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