The Preparation and Criteria of Purity of the Amino Acids

Abstract

Publisher Summary This chapter outlines the methods for the preparation, purification, and determination of purity of the commonly occurring amino acids because of its possible usefulness to investigators, who may require pure amino acids for experimental purposes. Consideration is given in the chapter only to the DL-, L-, and D-forms of the 21 amino acids that are shown to be constituents of proteins. Isolation procedures employed for the preparation of L-amino acids vary with the amino acid and the starting material. The DL-forms of all of the amino acids are prepared by racemization. The optically active amino acid is heated with a strong base, strong acid or an alkaline solution of acetic anhydride or ketene. Isolation procedures employed for the preparation of L-amino acids vary with the amino acid and the starting material. Some amino acids are readily separated from hydrolyzates of certain proteins by crystallization at their isoelectric points. The ones most commonly isolated in this manner are glutamic acid and leucine from cereal grains, leucine and tyrosine from blood proteins, and cystine from hair and other keratins. Arginine, histidine, and lysine are often removed by precipitation and their silver salts of phosphotungstates by electrodialysis, ion exchange, or by selective adsorption.