Alkaline phosphatase activity in Protogonyaulax tamarensis

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Abstract
A non-toxic strain of the marine dinoflagellate Protogonyaulax tamarensis (= Gonyaulax tamarensis has been isolated from a bloom in the Adriatic Sea, off the Emilia-Romagna coast. Cultures of the cells were grown in the laboratory in enriched seawater at various initial ambient orthophosphate (P i concentrations, ranging from 0.3 to 40.5 μM. The growth rate varied from 0.3 to 0.8 divisions day −1 depending on the P i concentration. Alkaline phosphatase activity was inversely proportional to ambient P levels. From measurements of kinetic parameters, the binding of the artificial substrate p -nitrophenylphosphate to the P.tamarensis alkaline phosphatase was quite strong (K m =50 μM). Maximal activity was observed at pH 8.4, although the pH-activity curve was broad, in contrast to that of other alkaline phosphatases. Protogonyaulax tamarensis alkaline phosphatase, measured over a 24h period, exhibited an apparent diurnal fluctuation in activity, in common with the enzyme from other dinoflagellates.