Oxygen in mammalian tissue: methods of measurement and affinities of various reactions

Oxygen is the primary oxidant in energy-producing biological reactions and is also involved in the synthesis and degradation of many structural and regulatory molecules of physiological importance. This review discusses the advantages and limitations of the currently available methods for measuring oxygen in mammalian tissue and bodily fluids. These include 1) the effects of O2 on the relaxation time of molecules excited by electromagnetic radiation and observed by optical (fluorescence and phosphorescence) and magnetic (nuclear magnetic resonance and electron paramagnetic resonance) techniques, 2) the polarographic and galvanic reduction of oxygen at metal surfaces, 3) in vivo spectrophotometry of intrinsic redox systems, 4) manometry and tonometry, and 5) mass spectroscopy. The values of tissue oxygenation obtained with these techniques are compared with the Michaelis constant values for oxygen of almost 60 oxygen-consuming enzymes involved in mammalian tissue metabolism.