Colorimetric Determination of ω-Amino Acids

A colorimetric method of determining minute amounts of ω-amino acids with high sensitivity, accuracy and reproducibility utilizing a modification of the Berthelot reaction is proposed, and the experiments leading to the establishment of the standard procedure are described. Sample solution (0.1–0.3 ml) is mixed with 0.2 m borate buffer (0.2 ml) and 6%phenol (1.0 ml). After cooling in ice water and adding 7.5% sodium hypochlorite solution (0.4 ml), the mixture is heated at 100°C for l0 min and promptly cooled. The optical density is read at 630 mμ. Most α-amino acids, except some basic ones, give no color reaction but interfere with the reaction if present in significant amounts. Primary amines, but not secondary ones, and ammonium salts also give positive reactions. Determination of the reaction velocity of pumpkin glut-amate decarboxylase [EC 4.1.1.15] is reported as an example of the application of this method for biochemical studies.