부산대학교 도서관

Inorganic carbon acquisition has been investigated in the marine prymnesiophytes Dicrateria inornata and Ochrosphaera neapolitana . The presence of external and internal carbonic anhydrase (CA) was detected in air-grown cells of D. inornata by potentiometric assay and corroborated by mass spectrometry. Growth on 3% CO 2 repressed external CA activity. Extracts of air-grown cells of O. neapolitana showed considerable internal CA activity, but no external CA activity was detected by mass spectrometry. Illumination of air-grown cells of D. inornata incubated with 100 μM H 13 CO 3 - and treated with the CA inhibitor acetazolamide caused a rapid drop in the extracellular CO 2 concentration to a level below its equilibrium concentration indicating that cells were actively taking up CO 2 from the medium. The rate of O 2 evolution at the CO 2 compensation concentration was higher than could be supported by the uncatalysed formation of CO 2 from HCO 3 - , demonstrating that the cells were taking up HCO 3 - directly. Similar results were obtained with air-grown cells of O. neapolitana. Active CO 2 transport in both species was not repressed by growth under high levels of CO 2 . The photosynthetic electron transport inhibitor 3-(3′, 4′-dichlorophenyl)-1,1-dimethylurea (DCMU) inhibited CO 2 uptake in air-grown cells of both species, demonstrating that the energy to support active CO 2 transport was derived from photosynthetic linear electron transport. These results show that the physiological characteristics of the CO 2 concentrating mechanism in related species do not appear to be correlated with the availability of CO 2 in the surrounding medium. [ABSTRACT FROM AUTHOR]