Reduction of oxidized guanosine by dietary carotenoids: a pulse radiolysis study.

Time-resolved pulse radiolysis investigations reported herein show that the carotenoids β-carotene, lycopene, zeaxanthin and astaxanthin (the last two are xanthophylls--oxygen containing carotenoids) are capable of both reducing oxidized guanosine as well as minimizing its formation. The reaction of the carotenoid with the oxidized guanosine produces the radical cation of the carotenoid. This behavior contrasts with the reactions between the amino acids and dietary carotenoids where the carotenoid radical cations oxidized the amino acids (tryptophan, cysteine and tyrosine) at physiological pH.