Studies on the tryptophan-dependent light emission by prostaglandin hydroperoxidase reaction

The chemiluminescence earlier observed upon the incubation of arachidonic acid with prostaglandin-synthesizing microsomes of sheep vesicular gland (Marnett et al. (1974) Biochem. Biophys. Res. Commun. 60, 1286-1294) was reinvestigated with prostaglandin endoperoxide synthetase purified from bovine vesicular gland microsomes. When the purified enzyme was incubated with arachidonic acid in the presence of hematin and tryptophan, a rapid light emission was observed. The fatty acid cyclo-oxygenase activity as demonstrated with manganese protoporphyrin was not responsible for the luminescence. When the hematin-requiring prostaglandin hydroperoxidase reaction (the conversion of prostaglandin G2 to H2) was carried out with tryptophan, skatole, or 3-indolepropionic acid, the light emission was observed, but not with either epinephrine or guaiacol in place of tryptophan. The light intensity was dependent on the concentration of enzyme, hematin, tryptophan, and prostaglandin G2. Various other hydroperoxides in addition to prostaglandin G2 were also active. The luminescence spectrum recorded by a spectrometer equipped with a filter spectral analyzer gave emission peaks around 500, 550, and 610 nm. The spectrum was distinguishable from that of singlet oxygen, and was similar to that reported for a photochemical reaction of tryptophan.