Singlet oxygen in biological systems

Abstract

Electronically excited molecular oxygen ( 2Δ g O 2) is of increasing interest in biology and medicine. Several methods have been employed for detection and identification, including chemical trapping and the continuous and non-invasive monitoring of low-level chemiluminescence in the visible and infrared spectral region due to the bi- and monomolecular transition of the excited molecules to the ground state. Performing spectral analysis and measuring the effect of D 2O and/or 1O 2 quenchers, evidence for the involvement of this reactive oxygen species in a variety of non-enzymatic and enzyme-catalyzed reaction pathways of biological and medical importance has been provided. The use of the intact perfused rat liver allowed direct monitoring of the metabolism of hydroperoxides and quinones by measuring the photoemission from the organ surface. Occurrence of 1O 2 in cells, generated under physiological conditions or under conditions of oxidative stress, has implications on biological functions at molecular and cellular level. Besides reaction with lipids, inactivation of several enzymes by means of amino acid modification has been demonstrated; also damage of constituents of DNA has been reported. Recently the effect of 1O 2 on the biological activity of intact DNA was investigated, showing the loss of transforming activity of pBR 322 in E. coli upon 1O 2 exposure. Quantification of 1O 2 has been performed during these measurements; quantification of steady states of 1O 2 in more complex systems remains the topic of present work.