We have been studying on a bioluminescence system of an oceanic luminous squid. Symplectoteuthis oualaniensis L. In 1981, Tsuji and Leisman reported that a homogenate of the luminous organ of this squid gave light in the presence of monocations such as Na^+, K^+ and molecular oxygen at pH 7.8. In 1993, we succeeded in the extraction of a photoprotein. named symplectin, responsible for the bioluminescence in a 0.6M KCl solution from the same squid S. oualaniensis collected in Okinawa, Japan. We reported that this photoprotein includes dehydrocoelenterazine(2) as the chromophore which covalen...