Rubisco protein
Template:BreadcrumbsPrimaryProduction
| Rubisco protein abundance |
|---|
| Approach: immunodetection or targeted mass spectrometry |
| Context: in situ, incubation, lab |
| Spatial scale: point sample |
| Temporal scale: minutes to hours |
| Units: mol protein per cell; mol protein L-1; protein mass fraction |
| Community captured: bulk to group-specific |
| Co-measurements: Single Turnover Chlorophyll Fluorescence; 14C or 13C fixation; total protein |
Method Overview
RuBisCO (ribulose-1,5-bisphosphate carboxylase/oxygenase) concentration is quantified in phytoplankton cell extracts or filtered field samples using immunodetection (Western blotting with antibodies raised against conserved RuBisCO epitopes) or targeted proteomics by mass spectrometry (MS). Antibody-based approaches use global antisera that recognize multiple RuBisCO forms across diverse taxa, allowing community-level estimates without prior taxonomic assignment. Targeted MS methods use selected-reaction monitoring (SRM) with synthetic peptide standards to quantify taxon-specific RuBisCO peptides, providing group-resolved Rubisco content[1].
When combined with kinetic constants for RuBisCO carboxylation and in situ temperature and CO2 concentrations, RuBisCO content can be used to model potential carbon fixation rates.
Scale of measurement
Each filtered sample provides a point measurement. Because protein turnover is slower than mRNA turnover, RuBisCO concentrations integrate the biosynthesis history over hours to days, providing a more stable signal than transcript measurements.
Data generated
RuBisCO concentrations per cell or per unit volume; when taxon-specific peptide standards are used, group-resolved estimates are obtained. Conversion to carbon fixation rates requires RuBisCO-specific kinetic constants (kcat, Km(CO2)).
Units & currency
Units are mol protein per cell, mg protein L-1, or protein mass fraction. The currency is protein (carbon fixation is a derived quantity).
Sample size
Typical samples are ~1 L in volume.
Repositories & databases
Limitations
Post-translational modifications and activation states (RuBisCO requires carbamylation and Mg2+ binding for activity) affect the relationship between protein abundance and actual carboxylation rate. Peptide standards and antibodies may not capture the full diversity of RuBisCO forms (Form I vs. Form II; α vs. β subunits) across the community. Accurate total protein per liter measurements in dilute open-ocean waters are technically challenging. Models linking RuBisCO content to carbon fixation are still under active development.
Example Applications & Protocols
Classic examples
- Orellana & Perry (1992) An immunoprobe to measure Rubisco concentrations and maximal photosynthetic rates of individual phytoplankton cells [2]
- Campbell et al. (2003) Analysing photosynthetic complexes in uncharacterized species or mixed microalgal communities using global antibodies [3]
Recent applications
- Young et al. (2024) Photosynthetic processes in Antarctic sea ice during the spring melt [1]
- Roberts et al. (2024) Rubisco in high Arctic tidewater glacier–marine systems: a new window into phytoplankton dynamics [4]
Common calculations/conversions
- Potential GPP = [Rubisco] × kcat(T) × [CO2] / (Km(CO2) + [CO2]); where kcat is temperature-adjusted.
References
- ↑ 1.0 1.1 Young, J. N., Rundell, S., Cooper, Z. S., Dawson, H. M., Carpenter, S. D., Ryan-Keogh, T., Rowland, E., Bertrand, E. M., & Deming, J. W. (2024). Photosynthetic processes in Antarctic sea ice during the spring melt. Limnology and Oceanography, 69, 1562–1576. https://doi.org/10.1002/lno.12596
- ↑ Orellana, M. V., & Perry, M. J. (1992). An immunoprobe to measure Rubisco concentrations and maximal photosynthetic rates of individual phytoplankton cells. Limnology and Oceanography, 37(3), 478–490. https://doi.org/10.4319/lo.1992.37.3.0478
- ↑ Campbell, D. A., Cockshutt, A. M., & Porankiewicz-Asplund, J. (2003). Analysing photosynthetic complexes in uncharacterized species or mixed microalgal communities using global antibodies. Physiologia Plantarum, 119(3), 322–327. https://doi.org/10.1034/j.1399-3054.2003.00175.x
- ↑ Roberts, M. E., Bhatia, M. P., Rowland, E., White, P. L., Waterman, S., Cavaco, M. A., Williams, P., Young, J. N., Spence, J. S., Tremblay, J.-É., Montero-Serrano, J.-C., & Bertrand, E. M. (2024). Rubisco in high Arctic tidewater glacier–marine systems: a new window into phytoplankton dynamics. Limnology and Oceanography, 69, 802–817. https://doi.org/10.1002/lno.12525