Ca2+-regulated photoproteins of ctenophores lose bioluminescence
activity when exposed to visible light. Little is known about the
chemical nature of chromophore photoinactivation. Using a total synthesis
strategy, we have established the structures of two unusual coelenterazine
products, isolated from recombinant berovin of the ctenophore Beroe abyssicola, which are Z/E isomers. We propose that during light irradiation, these derivatives
are formed from 2-hydroperoxycoelenterazine via the intermediate 8a-peroxide
by a mechanism reminiscent of that previously described for the auto-oxidation
of green-fluorescent-protein-like chromophores.