| Inorganic carbon acquisition has been investigated in two marine, unicellular haptophytes Isochrysis galbana Parke and Dicrateria inornata Parke. The presence of external and internal carbonic anhydrase (CA) was detected by potentiometric assay and mass spectrometry in both species.;CA was detected as several bands of strong activity on cellulose acetate plates after electrophoresis of extracts of air-grown Isochrysis , whereas those of high CO2-grown cells contained very low activity at the same positions. Three isoforms of CA in lysates of air-grown cells were found: a fast running form, which was not inhibited by AZA, and two slow running forms of CA which were completely inhibited by AZA. Two isoforms that were detected in high CO2-grown cells appeared to be intracellular forms. The fast running, AZA resistant form found in air-grown cells was the external CA.;The capacity of Isochrysis galbana to take up bicarbonate was examined by comparing the rate of photosynthetic O2 evolution with the theoretical photosynthetic rate that could be supported solely by CO2 arising from the spontaneous dehydration of bicarbonate in the external medium.;The occurrence of an active CO2 transport system was investigated by mass spectrometry in Isochrysis galbana and Dicrateria inornata. (Abstract shortened by UMI.). |
