Journal
PLANT CELL AND ENVIRONMENT
Volume 39, Issue 5, Pages 983-997Publisher
WILEY
DOI: 10.1111/pce.12629
Keywords
CO2; nutrients; nitrogen; photosynthesis; carbon reactions; carboxylation
Categories
Funding
- Australian Research Council [FT140100645]
- Australian Research Council [FT140100645] Funding Source: Australian Research Council
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Ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) is the cornerstone of photosynthetic carbon assimilation because it catalyses the fixation of CO2 onto ribulose-1,5-bisphosphate (RuBP). The enzyme also catalyses RuBP oxygenation, thereby evolving phosphoglycolate which is recycled along the photorespiratory pathway. Oxygenation is quantitatively important, because under ordinary gaseous conditions, more than one third of RuBP molecules are oxygenated rather than carboxylated. However, contrary to carboxylation, the chemical mechanism of oxygenation is not well known, and little progress has been made since the early 80s. Here, I review recent experimental data that provide some new insights into the reaction mechanism, and carry out simple calculations of kinetic parameters. Isotope effects suggest that oxygenation is less likely initiated by a redox phenomenon (such as superoxide production) and more likely involves concerted chemical events that imply interactions with protons. A possible energy profile of the reaction is drawn which suggests that the generation of the oxygenated reaction intermediate (peroxide) is irreversible. Possible changes in oxygenation-associated rate constants between Rubisco forms are discussed. Ribulose-1,5-bisphosphate carboxylase/oxygenase is the key enzyme of photosynthetic CO2 fixation and thus a considerable number of studies examined its kinetics and molecular properties. However, the chemical mechanism associated with O-2 fixation is not well known. This paper reviews hypotheses and describes the most plausible mechanism for oxygenation.
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