The presence of different carbonic anhydrase (EC 4.2.1.1) activities has been
investigated in the intertidal macroalgae Gracilaria sp.
and Enteromorpha intestinalis (L.) Nees by using
fractionation techniques. Activities, measured potentiometrically, were
recorded for all fractions in both species, including those containing
proteins associated with chloroplast membranes. In
Gracilaria sp., most of the total activity was present
in the soluble fraction, while similar activities were obtained for all
fractions in E. intestinalis. By using inhibitors with a
different capacity to enter the cell (acetazolamide and 6-ethoxyzolamide,
inhibitors of external and total activity, respectively), a surface-accessible
location was indicated for a high proportion of the soluble activity obtained
in Gracilaria sp. In
E. intestinalis, the inhibitor assays showed a
substantial dependence of photosynthesis on intracellular activity. The
short-term regulation of the extracellular activity in response to inorganic
carbon availability was also examined in both macroalgae. Rapid repression
(after 2 h) of the activity was recorded when Gracilaria
sp. was transferred from limited to replete carbon conditions, while a fairly
constant activity was recorded for E. intestinalis. In
contrast, an increase of external activity was obtained for both macroalgae
after being transferred to carbon-limited conditions, this response being more
pronounced in E. intestinalis. Our results suggest the
occurrence of a species-specific carbonic anhydrase system.
Carbonic Anhydrase Activity in Isolated Chloroplasts of Wild-Type and High-CO2-Dependent Mutants of Chlamydomonas reinhardtii as Studied by a New Assay
