Reaction rates of superoxide radicals with the essential amino acids

Upper limits for the rates of reaction of amino acids with superoxide radicals have been determined spectrophotometrically by the stopped flow method. Rate measurements at 23 degrees C for the reaction of HO2 with amino acids were made in the pH range between 1 and 2; similar measurements for O2- were taken near pH 10. The results show that, overall, amino acids are relatively unreactive toward both HO2 and O2-. Computed second-order rate constants for their interaction with HO2 range from 101 mol-1s-1 for aliphatic amino acids to about 600 1 mol-1s-1. The second-order rate constants for the interaction of amino acids with O2- are smaller and range from 0.1 to about 20 1 mol-1s-1.