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Low stable carbon isotope fractionation by coccolithophore RubisCO
Ist Teil von
Geochimica et cosmochimica acta, 2011-11, Vol.75 (22), p.7200-7207
Ort / Verlag
Elsevier Ltd
Erscheinungsjahr
2011
Quelle
Access via ScienceDirect (Elsevier)
Beschreibungen/Notizen
The
13C/
12C ratio of carbon compounds is used to identify sources and sinks in the global carbon cycle. However, the relatively enriched
13C 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 (
ε
=
11.1‰) against
13CO
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
13C by phytoplankton RubisCO may be a major factor influencing the enriched
13C content of marine organic carbon. This finding emphasizes the necessity of (a) determining
ε values for RubisCOs of other marine phytoplankton and (b) re-evaluation of
δ
13C values from physiological, environmental, and geological studies.