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Isoenzymic forms of carbonic anhydrase in the red macroalga Porphyra leucosticta
Author(s) -
Mercado Jesús M.,
Viñegla Benjamín,
Figueroa Félix L.,
Niell F. Xavier
Publication year - 1999
Publication title -
physiologia plantarum
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.351
H-Index - 146
eISSN - 1399-3054
pISSN - 0031-9317
DOI - 10.1034/j.1399-3054.1999.106110.x
Subject(s) - carbonic anhydrase , porphyra , botany , biochemistry , biology , chemistry , algae , enzyme
Different isoenzymes of carbonic anhydrase (CA; EC 4.2.1.1) have been separated using thalli of the red macroalga Porphyra leucosticta Thuret in Le Jolis. Homogenates of the thallus were centrifuged in order to separate soluble and membrane proteins. The fraction containing membrane proteins was subdivided by centrifuging into two fractions: green and nongreen membrane proteins. CA activity was detected in all the fractions. Because external CA (measured on intact thallus) represented 15% of total activity, it was concluded that most of the CA (ca. 80%) was soluble and internal. Direct evidence regarding the different function of external and internal CA was obtained by determining the effects on photosynthesis of two specific CA inhibitors with different capacity for entering cell. It was concluded that internal CA was necessary to ‘trap’ the CO 2 entering the cell and thus maintain a favorable CO 2 gradient that permits its diffusive entry. Changes in the O 2 evolution rate at inorganic carbon ( C i ) concentration saturating for photosynthesis and on the photosynthetic conductance for C i were found when external CA was inhibited. Based on these changes and the significant CA activity (ca. 9% of the total activity) found in nongreen membrane fraction, the presence of external CA associated with plasma membrane was postulated. The presence of CA associated with chloroplast membrane was also suggested.