A new method for the isolation of L-alanine and L-proline from protein hydrolysates.

The present investigation deals with the development of a convenient method for the isolation of alanine and proline from protein hydrolysates. In this work the authors aim to eliminate some of the objections inherent in the older methods (l-6). No expensive reagents are required for the separation of these amino acids, and high yields of the pure final products are secured. In a recent publication from this laboratory (7), a new method has been described for the isolation of glycine from protein hydrolysates by its direct precipitation as a complex salt with copper picrate. Subsequent work in this field has indicated that other heavy metal picrates yield complexes with amino acids sufficiently insoluble to offer the possibility that these substances may be used as precipitants for a variety of amino acids. Of the various metallic picrates tested, those of the alkaline earths have proved particularly valuable in this direction. It has been previously reported (7) that preliminary experiments with calcium picrate have demonstrated that this reagent forms highly insoluble complexes with a number of amino acids. Further study of the conditions under which this picrate can be employed as a precipitant for certain individual amino acids is still in progress. In the present article the investigation has been extended to include the study of the behavior of strontium picrate towards a-amino acids. It has been found that of the amino acids normally occurring in a protein hydrolysate only glycine, alanine, proline, phenylalanine, tryptophan, lysine, and arginine form sparingly soluble complex salts when treated with strontium picrate under the experimental conditions employed. The properties of both the alanine and proline complex salts with strontium picrate have been examined in some detail. Analysis of each of these complexes proved it to be composed of 1 mole of the amino acid combined with 1 mole of strontium picrate. These complexes are readily obtained from aqueous solutions containing the two components in equimolar ratio. They crystallize quickly from hot water in clusters of yellow needles. Alanineand proline-strontium picrate complexes are soluble in water to the extent of 1.25 and 1.20 gm. per 100 ml. at O”, respectively. Experiments with aqueous solutions of known alanine or proline content have