CHEMICAL-REACTION RATES OF AMINO-ACIDS WITH SINGLET OXYGEN

Abstract— The chemical reactions of amino acids with singlet oxygen have been measured in D2O solution where the singlet oxygen was generated directly by irradiation of the oxygen 3∑g‐→1δg+ lv electronic transaction with the 1.06 μm output of an Nd‐Yag laser. Chemical reaction was measured as amino acid loss by an amino acid analyzer or by fluorescence in the cases of tryptophan and tyrosine. The chemical rate constants, in units of 107M‐1s‐1, are histidine 10, tryptophan 3, methionine 1.7, tyrosine 0.8 and alanine 0.2, In the cases of histidine, methionine and alanine the interaction appears to be entirely chemical, i.e. there is no evidence for physical quenching in addition to the chemical reaction. The histidine chemical reaction rate constant shows an increase with pD with a pK of 6.9. Copyright © 1979, Wiley Blackwell. All rights reserved