Premium
Active transport of CO 2 by three species of marine microalgae
Author(s) -
Huertas I. Emma,
Colman Brian,
Espie George S.,
Lubian Luis M.
Publication year - 2000
Publication title -
journal of phycology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.85
H-Index - 127
eISSN - 1529-8817
pISSN - 0022-3646
DOI - 10.1046/j.1529-8817.2000.99142.x
Subject(s) - biology , extracellular , photosynthesis , carbonic anhydrase , seawater , biophysics , total inorganic carbon , carbon dioxide , biochemistry , botany , nuclear chemistry , enzyme , chemistry , ecology
The occurrence of an active CO 2 transport system and of carbonic anhydrase (CA) has been investigated by mass spectrometry in the marine, unicellular rhodophyte Porphyridium cruentum (S.F. Gray) Naegeli and two marine chlorophytes Nannochloris atomus Butcher and Nannochloris maculata Butcher. Illumination of darkened cells incubated with 100 μM H 13 CO 3 − caused a rapid initial drop, followed by a slower decline in the extracellular CO 2 concentration. Addition of bovine CA to the medium raised the CO 2 concentration by restoring the HCO 3 − –CO 2 equilibrium, indicating that cells were taking up CO 2 and were maintaining the CO 2 concentration in the medium below its equilibrium value during photosynthesis. Darkening the cell suspensions caused a rapid increase in the extracellular CO 2 concentration in all three species, indicating that the cells had accumulated an internal pool of unfixed inorganic carbon. CA activity was detected by monitoring the rate of exchange of 18 O from 13 C 18 O 2 into water. Exchange of 18 O was rapid in darkened cell suspensions, but was not inhibited by 500 μM acetazolamide, a membrane‐impermeable inhibitor of CA, indicating that external CA activity was not present in any of these species. In all three species, the rate of exchange was completely inhibited by 500 μM ethoxyzolamide, a membrane‐permeable CA‐inhibitor, showing that an intracellular CA was present. These results demonstrate that the three species are capable of CO 2 uptake by active transport for use as a carbon source for photosynthesis.