Luminescence and Raman spectroscopic studies on the damage of tryptophan, histidine and carnosine by singlet oxygen

In connection with the chemical modification of protein, the photooxidation of histidine (His), tryptophan (Trp) and carnosine by singlet oxygen O2) is investigated by a Eu3+ luminescence probe ATTA-Eu3+ and UV Raman spectroscopy under physiological conditions (pH 7.5). The solutions ontaining both the luminescence probe ATTA-Eu3+(1× 10−5 M) and the different concentration of the biological targets His, Trp or carnosine ere irradiated by a tungsten lamp in the presence of O2 photosensitizer H2TMPyP4 (1× 10−5 M), the luminescence intensity of the Eu3+ complex robe decreases linearly with increasing the concentration of the biological target. The reaction rate constants of O2 with His, Trp and carnosine ere calculated to be 3.2× 108, 7.7× 107 and 1.3× 108 M−1 s−1, respectively. The results suggest that the luminescence probe ATTA-Eu3+ can be sed for detecting the reactions of O2 with the biological targets quantitatively under physiological conditions. UV Raman spectroscopy probes he structural changes of these biological targets after reaction with O2, indicating that peroxides are main species for the reaction of Trp although he products decomposed by peroxides are main forms for that of His in a buffer solution. The imidazole ring of carnosine is the target of O2, and he peptide bond is almost intact after reaction with O2. 2007 Elsevier B.V. All rights reserved.