Intracellular localization of a carbonic anhydrase in Porphyridium purpureum (Porphyridiales, Rhodophyta)

Abstract

The intracellular localization of a carbonic anhydrase (CA) in the red alga, Porphyridium purpureum, was analysed by immunogold labelling experiments. A polyclonal antibody was raised against recombinant CA derived from cloned cDNA. Much higher CA activity was present in cells grown in ordinary air (low-CO2 cells) than in those grown in 5% CO2–enriched air (high-CO2 cells). An immunoblot analysis detected a single band in the low-CO2 cells, whereas no positive band was apparent in the high-CO2 cells. The antibody was used as a probe for immunogold labelling. The gold particles were predominantly localized along the plasma membrane of the low-CO2 cells, whereas no significant labelling was apparent in the high-CO2 cells. The exclusively intracellular localization of this CA activity and the absence of any membrane-spanning property of the enzyme suggests that the CA was associated with the cytoplasmic face of the plasma membrane. The results are discussed in relation to the possible role of CA.