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A NEW METHOD FOR ESTIMATING EXTERNAL, CARBONIC ANHYDRASE ACTMTY IN MACROALGAE 1, 2
Author(s) -
Mercado Jesús M.,
Figueroa F. L.,
Xauier Niell F.,
Axelsson Lennart
Publication year - 1997
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 - 10.1111/j.0022-3646.1997.00999.x
Subject(s) - carbonic anhydrase , acetazolamide , biology , steady state (chemistry) , biophysics , nuclear chemistry , biochemistry , enzyme , chemistry , physiology
The effects of external carbonic anhydrase (CA, E.C. 4.2.1.1) on HCO − 3 and CO 2 use under disequilibnum conditions were examined in 14 species of macroalgae. CO 2 was added to the algae in synthetic seawater free from inorganic carbon and buffered to pH 8.7. This resulted in a transient O 2 evolution, which was similar for most of the species tested: an initial rapid increase in the rate was followed by a gradual decrease, approaching a steady state within 10 min. The initial high rate of O 2 evolution was attributed to diffusive entry of CO 2 into the cells and the steady state to use of HCO − 3 . An enhancement of CO 2 diffusive entry was obtained with acetazolamide, an inhibitor of external CA activity. Using this enhancement, a variable was developed to quantify the degree to which CO 2 entry into the cell was prevented by the external CA. This variable, CA (%), was used as a measure of the external CA activity of the alga. Comparative measurements of the external CA activity using a potentiomtric method revealed that the new method was able to detect low levels of external CA activity, where the potentiometric method failed. These two different methods could be used together to increase the reliability of the measurements. The new method was useful for red and brown macroalgae and for those green macroalgae that lacked direct HCO 3 uptake. Thus prominent external CA activity was found for Valonia utricularis (green), Halopteris scoparia (brown), and Osmunda pinnatifida (red), where the potentiometric method failed, or nearly failed, to indicate any external CA activity. Direct uptake of HCO − 3 interfered with the new method and the degree of this interference was dependent on the magnitude of the uptake.