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 dip eptides, we have studied quenching of singlet molecular oxygen (O-1(2) ) by carnosine (beta-alanyl-L-histidine), its structural components (L -histidine, imidazole, and beta-histidine), ergothioneine (2-thiol-L-h istidine-betaine) taurine (2-aminoethanesulfonic acid) in aqueous (D2O , pD 7) solutions by using monitoring of O-1(2)-phosphorescence (1270- nm). The rate constants of O-1(2) quenching (K-q) by carnosine, anseri ne, and ergothioneine were shown to be similar [(3+/-1)x10(7) M(-1)s(- 1)]. Their values resembled those of free L-histidine [K-q=(4+/-1)x10( 7) M(-1)s(-1)] and imidazole [K-q=(2+/-1)x10(7) M(-1)s(-1)]. Non-aroma tic amino acids - taurine and beta-alanine - showed very low quenching activities (K-q<3x10(3) M(-1)c(-1)). The K-q values did not correlate with the literature data on abilities of the tested compounds to stim ulate muscle working capacities and inhibit myeloperoxidase-catalyzed oxygenation. Thus, the dipeptides can be used as potent water-soluble protectors against O-1(2) attack whereas their natural biochemical fun ctions are most probably determined by the processes of different natu re.