CIRCADIAN RHYTHMICITY OF TRYPTOPHAN-HYDROXYLASE IN THE MARINE DINOFLAGELLATE GONYAULAX-POLYEDRA STEIN AND THE ROLE OF TRYPTOPHAN HYDROXYLATION IN BIOLUMINESCENCE

In the bioluminescent dinoflagellate Gonyaulax polyedra, tryptophan hy droxylase activity exhibits a circadian rhythm of high amplitude, whic h persists in constant light. The maximum is found in the middle of ph otophase. Melatonin or exposure to a decreased temperature (15 degrees C), a treatment leading to melatonin accumulation, suppresses tryptop han hydroxylase activity. 5-Hydroxytryprophan, but not tryptophan, sti mulates bioluminescence. The dosage dependence of this effect of 5-hyd roxytryptophan is similar to that of its metabolite serotonin. These a ctions seem to be due to the further conversion to a much more potent metabolite, 5-methoxytryptamine. Inhibition of tryptophan hydroxylase by p-chlorophenylalanine, p-fluorophenylalanine or 5-fluorotryptophan decreases light emission. This inhibition can be overcome by addition of various indolic metabolites originating from the tryptophan hydroxy lation pathway, in particular, 5-hydroxycryptophan, serotonin, melaton in and 5-methoxytryptamine. Copyright (C) 1996 Elsevier Science Inc.