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Protocols in ecological and environmental plant physiology

 

Article << Previous     |     Next >>   Contents Vol 32(4)

Carbon isotope effect predictions for enzymes involved in the primary carbon metabolism of plant leaves

Guillaume Tcherkez A B, Graham D. Farquhar A

A Environmental Biology Group, Research School of Biological Sciences, Institute of Advanced Studies, Australian National University, GPO Box 475, Canberra, ACT 2601, Australia.
B Current address: Laboratoire Structure et Métabolisme des Plantes, Bat. 630, Institut de Biotechnologie des Plantes, Centre Scientifique d’Orsay, Université Paris XI, 91405 Orsay Cedex, France.
Corresponding author. Email: guillaume.tcherkez@ese.u-psud.fr

 
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Abstract

Carbon isotope effects of enzymes involved in primary carbon metabolism are key parameters in our understanding of plant metabolism. Nevertheless, some of them are poorly known because of the lack of in vitro experimental data on purified enzymes. Some studies have focused on theoretical predictions of isotope effects. Here we show how quantum chemical calculations can be adapted for calculation of isotope effects for the Rubisco-catalysed carboxylation and oxygenation reactions and the citrate synthase reaction. The intrinsic isotope effect of the carboxylation by Rubisco appears to be much smaller than previously thought, being close to the overall isotope effect of the reaction that is, between 25 and 30 per mil. The same applies to the enzyme citrate synthase, that catalyses the first step of the Krebs cycle, with an isotope effect of around 23 per mil. Combined with the isotope effects of equilibrium reactions calculated with β-factors, the Krebs cycle then has an overall isotope effect that depletes organic acids in 13C.

Keywords: carbon isotopes, carbon metabolism, carboxylation, citrate synthase, enzymes, oxygenation, Rubisco.


   
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