A Method for Estimating Glycine in the Presence of Excess Glutamate with ö-Phthaldialdehyde

We present a method to determine concentrations o f glycine between 1 and 3 mM in the simultaneous presence o f 2 5 -lO O m M glutamate, which is a modification o f the procedure originally described by Klein and Linser, Z. Physiol. Chem. 205, 251 (1932). Glycine and glutamate react with 150 m M o-phthaldialdehyde, glycine is quantitatively con­ verted into a colored o-phthaldialdehyde-glycine-glutamate complex. By recording the ab­ sorbance o f the complex at its maximum peak (around 540 nm), at 600 nm and 480 nm and applying a correction formula is possible to obtain a very good linear correlation when plot­ ting the values o f corrected absorbance versus the concentration o f glycine. From these plots an extinction coefficient o f 7.0 * 102 cm -1 m “ 1 was calculated for the complex. The method is highly reproducible and sensitive and solved the problem o f glutamate interference when esti­ mating low concentrations o f glycine in mixture containing 10 to 50 times concentrations of the former aminoacid.