Physiological production of singlet molecular oxygen in the myeloperoxidase-H2O2-chloride system

The putative role of singlet oxygen (O-1(2)) in the respiratory burst of neutrophils has remained elusive due to the lack of reliable means to study its quantitative production. To measure O-1(2) directly from biological or chemical reactions in the near infrared region, we have developed a highly sensitive detection system which employs two InGaAs/InP pin photodiodes incorporated with a dual charge integrating amplifier circuit. Using this detection system, we detected light emission derived from a myeloperoxidase (MPO)-mediated reaction in physiological conditions: pH 7.4, 1-30 nM MPO, 10-100 mu M H2O2 and 100-130 mM Cl- in place of Br- without the use of deuterium oxide. The MPO-H2O2-Cl- system exhibited a single emission peak at 1.27 mu m with a spectral distribution identical to that of delta singlet oxygen, Our results suggest physiological production of O-1(2) in the MPO-H2O2-Cl- system at an intravacuolar neutral pH. The MPO-mediated generation of O-1(2), which may have an important role in host defense mechanisms, is discussed in connection with previous results. (C) 1999 Federation of European Biochemical Societies.