Chemistry, clones, and circadian control of the dinoflagellate bioluminescent system. The Marlene DeLuca memorial lecture.
Bioluminescence in the dinoflagellate Gonyaulax polyedra occurs as brief bright flashes, originating from many (approximately 400) small (approximately 0.5 microns) cytoplasmic organelles which protrude into the acidic vacuole, and are thus surrounded by the tonoplast. Biochemically, the substrate is unusual; it is an open chain tetrapyrrole, highly unstable to air but protected in the cell at pH 8 by virtue of a luciferin binding protein (LBP). This molecule is a dimer of 72 kDa subunits which, upon a decrease in pH, releases luciferin to react with oxygen in the luciferase (approximately 140 kDa) catalysed luminescent reaction. cDNAs for both luciferase and LBP have been isolated and cloned, and the identity of LBP was confirmed by hybrid selection and in vitro translation of the message. The tenfold circadian (day to night) change in the amount of LBP, which parallels the in vivo rhythm of luminescence, is due to de novo synthesis and subsequent degradation of the protein each day. The LBP mRNA levels, as determined by in vitro translations and by Northern hybridizations, do not vary over the daily cycle, indicating that circadian control of bioluminescence in this species is mediated at the level of translation.