Crystalline luciferin from a luminescent fish, Parapriacanthus beryciformes.

Biochemical research on luminescent enzyme-substrate ("luciferin-luciferase") systems has resulted thus far in the isolation and crystallization of the luciferin from only two types of luminescent organisms, namely, the firefly1 and the small ostracod crustacean, Cypridina.2 Synthesis of the former luciferin has very recently been achieved,3 and a tentative structure proposed for the latter luciferin,4 which is a considerably more complicated molecule. Both differ chemically from the diffusible factors involved in bacterial luminescence.5 The present study has resulted in crystallization of luciferin from one of the two examples of luminescent fishes; namely, Parapriacanthus beryciformes6 and Apogon (marginatus) ellioti,7 which have yielded crude aqueous extracts of luciferin and luciferase that emit light on mixing at room temperature. The essential components of the two systems react interchangeably, and those of Apogon have been shown to cross-react with the luciferin and luciferase of Cypridina.7 Present experiments have revealed that luminescent cross-reactions occur among all three of these systems. A total of over 4,000 specimens of Parapriacanthus was collected at Tateyama,8 Japan, and brought, packed in dry ice, to the Tokyo Kyoiku University, where the small, superficially embedded, ventral light organs were grossly removed and ground in a mortar chilled with dry ice. A very small amount of crystalline luciferin was obtained from such brei by the procedure of Shimomura et al.2 as recently modified by Haneda et al. for crystallizing Cypridina luciferin,9 involving initial extraction with methanol at low temperatures (circa 20°C) and chromatographing a butanol solution of the de-fatted residue on an alumina column. A much larger quantity, amounting to about 20 mg of pure crystalline luciferin, was obtained by the same procedure from the pyloric caeca dissected from some 2,300 specimens (Fig. 1). The anatomical and histological details of the caeca remain to be worked out, but they appear to be connected by a minute duct to the light organs, and they evidently store luciferin. The intact caeca are nonluminous, and likewise the brei resulting from grinding with water, but a brilliant luminescence results on addition of Cypridina luciferase to the brei. In the stomachs of about a dozen of the 2,300 specimens, a few individual Cypridina, dead but still luminous, were discovered. This fact, plus observation of a luminescent reaction of crystallized luciferin from the fish with purified luciferase of Cypridina, and chemical similarities found between the luciferins from the two different sources (see below) raises the question as to whether Parapriacanthus depends on ingested Cypridina as the chief or sole source of its luciferin. While this possibility cannot be rigidly excluded on the basis of present evidence, it would present a fantastic situation