Tracing oxygen metabolism by use of positron emitter oxygen-15

Oxygen, an essential molecule for life, is utilized not only for cellular respiration but also for biosynthesis and metabolism of various important biomolecules such as steroids, eicosanoids, and neuroactive substances. Since the oxygenases, oxygen-fixating enzymes, were found in 1950s, only stable isotopes (17O and 18O) have been utilized as a tracer for demonstration of oxygen incorporation into organic substances. This stable isotopic method is established, but is hardly applicable to complicated (crude and multi-cellular) systems. Therefore, we here developed a novel radiotracer technique for oxygen metabolism that employs the positron emitter 15O2, whose physical half-life is 2.07 min. In a model reaction with metapyrocatechase, one of the well-known dioxygenases, the substrate catechol was converted to the radioactive product which was identified as alpha-hydroxymuconic epsilon-semialdehyde by a very sensitive LC-radio-UV-MS combined method.