GB658669A - Improvements in or relating to the preparation of one or more basic amino acids from a mixture of amino acids - Google Patents

Abstract

One or more basic amino acids are separated from a mixture of amino acids by passing a solution of the mixture through a bed or column of "carboxylic type" ion-exchange resin containing carboxylic acid groups and carboxylic salt groups in a ratio that has been adjusted so that the pH of the amino acid solution in contact with the resin is maintained below the isoelectric point of the acid or acids to be adsorbed and above that of the acid or acids not to be adsorbed, and thereafter eluting adsorbed acid from said resin. The "carboxylic type" resins are those wherein the cation-adsorbing groups are carboxyl groups, and are made by copolymerizing styrene, maleic anhydride, and a compound containing non-conjugated double bonds, one in a CH2=C< grouping, or by copolymerizing an acrylic acid CH2= CR-COOH with a compound having two non-conjugated double bonds, as described in U.S.A. Specifications 2,340,110 and 2,340,111. Adjustment of the ratio of acid to salt groups in the resin is effected by converting it to its sodium, ammonium or other alkali metal salt by treating with alkali hydroxide solution, and adding a buffer solution such as sodium acetate-acetic acid or containing other salts of strong bases and weak acids, e.g. alkali metal salts of phosphoric, citric, propionic or phthalic acid. A resin which operates at pH 6.3-7.6 to adsorb basic amino acids but not neutral or acidic is prepared by treating the sodium salt of the resin with a buffer of pH 4.2-5.5. A resin may be prepared to operate at pH 7.6-9.7 to adsorp arginine and lysine but not histidine by using a buffer of pH 5.8-7.5. By a sequence of operations, separation in steps may be effected. Two beds of resin may sometimes be used in each step. The resin may be treated with 0.1 N sodium hydroxide to form the salt, rinsed with water until the effluent has a pH of 10, treated with buffer solution of the proper pH, and again rinsed. The solution of amino acids should have a pH approximately that to prevail in the column. A flow rate of 1 volume of 0.1 per cent amino acid solution per 10 volumes of resin per minute is suitable. Removal of adsorbed acid may be effected with strong or weak acids, e.g. 0.01 N mineral acid or aqueous solutions of carbon dioxide under pressure, or with alkali such as sodium hydroxide or ammonia solution. Protein hydrolysates made with strong mineral acids are treated by steam distillation or by addition of an acid-adsorbing resin such as is described in Specification 556,622 to raise the pH to about 3 without amino acids being adsorbed. The preferred carboxylic type resins are derived from acrylic, methacrylic or maleic acid and an aromatic divinyl compound such as divinyl benzene or naphthalene. The latter is generally present in amount of less than 10, preferably 5, per cent. In examples: (1) a mixture containing arginine, lysine, histidine, leucine, and glutamic acid is passed through divinyl benzene-methacrylic acid resin which has been treated with sodium hydroxide and a buffer of pH 4.7, arginine, lysine, and histidine being adsorbed; (2) arginine and lysine are separated from histidine using a buffer of pH 7.0; (3) a mixture of amino acids as in (2) but of pH about 10 is treated with the resin converted to sodium salt, only arginine being adsorbed, the effluent being neutralized and treated with resin to which a buffer of pH is added, the remaining arginine and lysine being adsorbed.