A New Method for Isolating I-(+)-lysine

None of the methods which have been used for isolating Z-(+)lysine from plant extracts and protein hydrolysates is ideal. The oldest method utilizes phosphotungstic acid to precipitate the basic nitrogenous compounds which must be fractionated subsequently (1, 2). In the Kossel-Kutscher silver sulfate-barium hydroxide fractionation (3) the lysine remaining in the final filtrate must be precipitated successively as phosphotungstate and picrate (4). The use of aromatic aldehydes (5) does not obviate the necessity for large amounts of phosphotungstic acid. Electrophoresis (6, 7) at defined hydrogen ion concentrations to separate the basic amino acids requires a special cell and a source of high voltage direct current, and the yields of lysine isolated as the picrate are not always uniform (6). Recently a simplified method, which is based upon a direct precipitation of the picrate, has been proposed which works well with some proteins but fails entirely with gelatin (8). A technique for isolating I-(+)-lysine has been devised which eliminates some of the objections inherent in the older methods. The new method consists of the conversion of the amino acids to their copper salts, followed by benzoylation of those reactive groups not masked by coordination with the cupric ion. E-Benzoyl-Z-(+)-lysine copper(I1) precipitates from the reaction mixture and may be converted, successively, into E-benzoyl-Z-( +)lysine and I-( +)-lysine dihydrochloride.