Circadian rhythmicity of tryptophan hydroxylase in the marine dinoflagellate gonyaulax polyedra stein and the role of tryptophan hydroxylation in bioluminescence

Abstract

In the bioluminescent dinoflagellate Gonyaulax polyedra, tryptophan hydroxylase activity exhibits a circadian rhythm of high amplitude, which persists in constant light. The maximum is found in the middle of photophase. Melatonin or exposure to a decreased temperature (15°C), a treatment leading to melatonin accumulation, suppresses tryptophan hydroxylase activity. 5-Hydroxytryptophan, but not tryptophan, stimulates bioluminescence. The dosage dependence of this effect of 5-hydroxytryptophan is similar to that of its metabolite serotonin. These actions 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-fluoro-tryptophan decreases light emission. This inhibition can be overcome by addition of various indolic metabolites originating from the tryptophan hydroxylation pathway, in particular, 5-hydroxytryptophan, serotonin, melatonin and 5-methoxytryptamine.