Abstract
External alkaline phosphatase activity (APA) has been measured in Porphyra umbilicalis (L.) Kutzing over an ecological range of temperature, pH, salinity, photon irradiance and external phosphate. Temperature, pH, salinity and external phosphate caused significant changes in APA. On the contrary, photon irradiance caused no significant effect. In the range of temperature assayed, maximum APA was 249 μmol pNP g dry wt −1 h −1 at 30 °C. With regard to pH, maximum activity occurred at pH 8.8 (249 μmol pNP g dry wt −1 h −1), whereas varying salinity, maximum enzymatic activity (270 μmol pNP dry g wt −1 h −1) took place at 43.75%. As expected, there was an inverse relationship between APA and external phosphate concentration. There is a minimum constant activity at phosphate concentration over 14 μM and a final inhibition of 71% in enzymatic activity.
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