A pulse radiolysis study of carnosine in aqueous solution

PURPOSE: To investigate the potential antioxidative role of carnosine (beta-alanyl-L-histidine) through its interaction with radiation induced radicals. MATERIALS AND METHODS: Pulse radiolysis experiments were performed by a 12 MeV electron linear accelerator (LINAC) on carnosine aqueous solutions at different pHs. The Raman spectra of solid samples were obtained by a Bruker IFS 66 spectrometer. RESULTS: The protonation state of the imidazole ring was observed to affect the site(s) of .OH attack on carnosine as well as the decay rates of the resulting adducts. Reasonably, a base catalysed water elimination from the adducts leading to a resonance-stabilized radical, which absorbs at lambda = 270 nm, takes place. Raman spectra in slightly alkaline medium have indicated that carnosine is mainly present as tautomer I and, of consequence, positions C(2) and C(4) of the imidazole ring are the preferential sites for .OH attack. CONCLUSIONS: These studies have shown that carnosine is a good scavenger of .OH radicals giving rise to a quite stable intermediate which should be less reactive towards other biological components than .OH itself. Raman data have been helpful in predicting the preferential sites for the .OH attack.