Quenching of singlet molecular oxygen by carnosine and related antioxidants. Monitoring 1270-nm phosphorescence in aqueous media.

In order to elucidate the biochemical roles of imidazol-containing dipeptides, we have studied quenching of singlet molecular oxygen (1O2) by carnosine (beta-alanyl-L-histidine), its structural components (L-histidine, imidazole, and beta-alanine), and related natural free-radical scavengers-L-anserine (beta-alanyl-1-methyl-histidine), ergothioneine (2-thiol-L-histidine-betaine), and taurine (2-aminoethanesulfonic acid) in aqueous (D2O, pD 7) solutions by using monitoring of 1O2-phosphorescence (1270-nm). The rate constants of 1O2 quenching (Kq) by carnosine, anserine, and ergothioneine were shown to be similar [(3 +/- 1) x 10(7) M-1s-1]. Their values resembled those of free-L-histidine [Kq = (4 +/- 1) x 10(7) M-1s-1] and imidazole [Kq = (2 +/- 1) x 10(7) M-1s-1]. Non-aromatic amino acids-taurine and beta-alanine-showed very low quenching activities (Kq < 3 x 10(3) M-1c-1). The Kq values did not correlate with the literature data on abilities of the tested compounds to stimulate muscle working capacities and inhibit myeloperoxidase-catalyzed oxygenation. Thus, the dipeptides can be used as potent water-soluble protectors against 1O2 attack whereas their natural biochemical functions are most probably determined by the processes of different nature.