A RAPID COLORIMETRIC METHOD FOR THE DETERMINATION OF LYSINE IN PROTEIN HYDROLYSATES

Abstract

A solution of chlorinated lysine develops a blue color when heated with phosphomolybdic–phosphotungstic acid. This color reaction, which will detect lysine at a concentration of 1 p.p.m., has been made the basis of a sensitive and rapid colorimetric method for the determination of lysine. Lysine and arginine are quantitatively separated from the other amino acids in a protein hydrolysate by adsorption on Decalso and the lysine content of the eluate is determined in the presence of arginine (which does not give the color reaction) by applying the color reaction after chlorination. Satisfactory recoveries of added lysine have been obtained from mixtures of amino acids and from a gelatin hydrolysate. The lysine content of several proteins has been determined and the results compared with those in the literature. In general the values obtained by the colorimetric method are intermediate between those obtained by isolation procedures and those by microbiological methods. The result of a determination on crystalline bovine serum albumin checked closely with the value obtained by the isotope dilution method.