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

Abstract

In order to elucidate the biochemical roles of imidazol‐containing dipeptides, we have studied quenching of singlet molecular oxygen (1O2) by carnosine (β‐alanyl‐L‐histidine), its structural components (L‐histidine, imidazole, and β‐alanine), and related natural free‐radical scavengers ‐ L‐anserine (β‐alanyl‐l‐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)×107 M‐1s‐1]. Their values resembled those of free L‐histidine [Kq=(4±1)×107 M‐1s‐1] and imidazole [Kq=(2±1)×107 M‐1s‐1]. Non‐aromatic amino acids ‐ taurine and β‐alanine ‐ showed very low quenching activities (Kq<3×103 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 102 attack whereas their natural biochemical functions are most probably determined by the processes of different nature.