Mathematics – Logic
Scientific paper
Nov 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011gecoa..75.7200b&link_type=abstract
Geochimica et Cosmochimica Acta, Volume 75, Issue 22, p. 7200-7207.
Mathematics
Logic
Scientific paper
The 13 C/ 12 C ratio of carbon compounds is used to identify sources and sinks in the global carbon cycle. However, the relatively enriched 13 C content observed for marine organic carbon remains enigmatic. The majority of oceanic carbon is fixed by algae and cyanobacteria via the Calvin-Benson-Bassham cycle, yet isotopic discrimination by the CO 2 fixation enzyme, RubisCO (ribulose 1,5-bisphosphate carboxylase/oxygenase), has only been measured for a single marine cyanobacterium. Different forms of RubisCO occur in different phytoplankton species (overall amino acid identity varying by as much as ˜75%) and thus may vary in the degree to which they fractionate carbon. Here we measured isotope discrimination by RubisCO from the coccolithophore Emiliania huxleyi , a cosmopolitan species used as a marine algal model . E. huxleyi RubisCO discriminated substantially less ( &z.epsiv; = 11.1‰) against 13 CO 2 than other RubisCO enzymes (18-29‰), despite having Michaelis-Menten kinetic parameters ( K CO 2 = 72 μM; V max = 0.66 μmol min -1 mg -1 protein) similar to those measured for RubisCO enzymes from different organisms. If widespread, decreased isotope discrimination of 13 C by phytoplankton RubisCO may be a major factor influencing the enriched 13 C content of marine organic carbon. This finding emphasizes the necessity of (a) determining &z.epsiv; values for RubisCOs of other marine phytoplankton and (b) re-evaluation of δ 13 C values from physiological, environmental, and geological studies.
Boller Amanda J.
Cavanaugh Colleen M.
Scott Kathleen M.
Thomas Phaedra J.
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