The kinetic properties of ribulose-1,5-bisphosphate carboxylase/oxygenase may explain the high apparent photosynthetic affinity of Nannochloropsis sp. to ambient inorganic carbon

Dan Tchernov, Alexander Livne, Aaron Kaplan, Assaf Sukenik

Research output: Contribution to journalArticlepeer-review

12 Scopus citations

Abstract

The marine unicellular alga Nannochloropsis sp. (Eustigmatophyceae) exhibits high apparent affinity for extracellular inorganic carbon (Ci) despite the fact that its ability to accumulate Ci within the cells is relatively low. Kinetic investigation of carboxylation enzyme, ribulose-1,5-bisphosphate carboxylase/oxygenase (RubisCO), isolated from Nannochloropsis suggests that the latter discrepancy can be accounted for by the high affinity of RubisCO for CO2. A Km(CO2) of 7-10 μM was obtained both by a standard radiolabeling approach and by novel methodology using membrane inlet mass spectrometry. The latter allows precise determination of the changes in the concentrations of dissolved CO2 and O2 as the reaction proceeds. The kinetic parameters of the oxygenase reaction, deduced from measurements of oxygen level, indicated a high Km(O2) (about 1 mM) and high Vmax (3.9 μmol O2 min -1 mg-1 protein) values, compared to those observed in green algae. Thus, despite Nannochloropsis RubisCO's low Km(CO 2), an unusually low specificity factor of 27 was calculated, lower than observed in cyanobacteria and close to values found in anaerobic organisms. We proposed that the elevated CO2 level within the cells, indicated by massive net efflux of CO2 during steady state photosynthesis, is essential for its growth under the high O2 concentrations prevailing in the environment.

Original languageEnglish
Pages (from-to)37-44
Number of pages8
JournalIsrael Journal of Plant Sciences
Volume56
Issue number1-2
DOIs
StatePublished - 1 Dec 2008
Externally publishedYes

Keywords

  • Inorganic carbon
  • Membrane inlet mass spectrometry
  • Nannochloropsis
  • Ribulose-1,5-bisphosphate carboxylase/oxygenase
  • RubisCO
  • Specificity factor

ASJC Scopus subject areas

  • Ecology, Evolution, Behavior and Systematics
  • Agronomy and Crop Science
  • Plant Science

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