Viewpoint: How large is the carbon isotope fractionation of the photorespiratory enzyme glycine decarboxylase?

Guillaume Tcherkez

Research output: Contribution to journalArticlepeer-review

54 Citations (Scopus)

Abstract

Despite the intense effort developed over the past 10 years to determine the 12C/13C isotope fractionation associated with photorespiration, much uncertainty remains about the amplitude, and even the sign, of the 12C/13C isotope fractionation of glycine decarboxylase, the enzyme that produces CO2 during the photorespiratory cycle. In fact, leaf gas-exchange data have repeatedly indicated that CO2 evolved by photorespiration is depleted in 13C compared with the source material, while glycine decarboxylase has mostly favoured 13C in vitro. Here I give theoretical insights on the glycine decarboxylase reaction and show that (i), both photorespiration and glycine decarboxylation must favour the same carbon isotope-the in vitro measurements being probably adulterated by the high sensitivity of the enzyme to assay conditions and the possible reversibility of the reaction in these conditions, and (ii), simplified quantum chemistry considerations as well as comparisons with other pyridoxal 5′-phosphate-dependent decarboxylases indicate that the carbon isotope fractionation favour the 12C isotope by ∼20‰, a value that is consistent with the value of the photorespiratory fractionation (f) obtained by gas-exchange experiments.

Original languageEnglish
Pages (from-to)911-920
Number of pages10
JournalFunctional Plant Biology
Volume33
Issue number10
DOIs
Publication statusPublished - 2006
Externally publishedYes

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