36 BIOLUMINESCENCE OF DINOFLAGELLATES AND KRILLS

The bioluminescence of dinoflagellates involves air-oxidation of luciferin (enzyme substrate) by luciferase (enzyme). On the other hand, Euphausia krills utilize highly fluorescent substance F not only as the catalyst for air-oxidation of a protein but also as the light-emitter. Fluorescent substance F exhibits chemical properties similar to those of dinoflagellate luciferin. Using alumina and ion exchange chromatography at low temperature under inert atmosphere (Sheme 1), the substance F (1) was successfully isolated from Euphausia pacifica. The structure of F was elucidated on the basis of degradation reaction summarized in Fig. 1 as well as the spectroscopic data of F (1) and oxy-F (2). The ring D part of the proposed structure, including relative stereochemistry, was unambiguously established by chemical means; ozonolysis of F, followed by CH_2N_2 treatment, yielded the expected product 7, the structure of which was determined by chemical synthesis. Dinoflagellate luciferin could be isolated from the dinoflagellate Pyrocystis lunula (Scheme 2). The structures of luciferin 8, oxidized luciferin 9 and blue compound 10 were elucidated by comparing their spectroscopic data with those of fluorescent substance F and oxy-F. Dinoflagellate luciferin and krill fluorescent substance F are apparently a member of the bile pigments. To the best of our knowledge, however, these are the first naturally occurring bile pigments, which structurally relate to chlorophylls rather than to haems. Studies on the mechanism of dinoflagellate bioluminescence is in progress