The widespread occurrence and tissue distribution of the imidazolopyrazine luciferins

Bioluminescence has been reported to occur in 17 phyla and at least 700 genera. However, the luciferin chemistry of the majority of luminous organisms has yet to be determined. The most common chemistry which is known to occur in deep sea bioluminescence is imidazolopyrazine bioluminescence. The main aim of this study was to examine the phyletic and tissue distribution of imidazolopyrazine luciferins. This will facilitate analysis of imidazolopyrazine bioluminescence at the cellular and molecular levels and, in particular, how and when its chemistry is controlled and expressed in vivo. Assays for both known imidazolopyrazines were established and a range of fresh organisms and tissue were analysed, i.e. fish, cephalopods, copepods, ostracods, amphipods and euphausiids. The main findings were that the number of genera in which coelenterazine has been detected has been increased from 52 to about 90. Also, for the first time, the other known imidazolopyrazine luciferin, Vargula-type luciferin, was quantified in the ostracod Cypridina dentata, but was not detected in any of its potential predators. Neither imidazolopyrazine luciferin was found in several luminous stomiiform fish assayed. Coelenterazine was measured in the livers and photophores of a number of cephalopods and it is apparent that coelenterazine is responsible for both modes of luminescence.