ALKALINE-PHOSPHATASE ACTIVITY IN PORPHYRA-UMBILICALIS (L) KUTZING

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-mu-mol pNP g dry wt-1 h-1 at 30-degrees-C. With regard to pH, maximum activity occurred at pH 8.8 (249-mu-mol pNP g dry wt-1 h-1), whereas varying salinity, maximum enzymatic activity (270-mu-mol pNP g dry wt-1 h-1) took place at 43.75 parts per thousand. As expected, there was an inverse relationship between APA and external phosphate concentration. There is a minimum constant activity at phosphate concentration over 14-mu-M and a final inhibition of 71% in enzymatic activity.