Reaction with O 2 instead of CO 2 leads to photorespiration and the consequent loss of fixed carbon, nitrogen and energy (Keys 1986). In spite of the pivotal role of the enzyme ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) in determining photosynthetic capacity, this enzyme manifests important catalytic inefficiencies arising from slow turnover and poor discrimination between CO 2 and O 2 (Tcherkez et al. This crucial information provides candidate amino acid replacements, which could be implemented to optimize crop photosynthesis under a range of environmental conditions. Phylogenetic analysis identified 13 residues under positive selection during evolution towards specific Rubisco kinetic parameters. This variability in kinetics was related to the amino acid sequence of the Rubisco large subunit. In species adapted to particular environments, including carnivorous plants, crassulacean acid metabolism species and C 3 plants from aquatic and arid habitats, Rubisco has evolved towards increased efficiency, as demonstrated by a higher k cat c/ K c ratio. The trade-off between K c and k cat c was not universal among the species studied and deviations from this relationship occur in extant forms of Rubisco. One evolutionary adaptation to a decreasing atmospheric CO 2/O 2 ratio has been an increase in the affinity of Rubisco for CO 2 ( K c falling), and a consequent decrease in the velocity of carboxylation ( k cat c), which in turn has been ameliorated by an increase in the proportion of leaf protein accounted by Rubisco. Our findings confirm that past atmospheric CO 2/O 2 ratio changes and present environmental pressures have influenced Rubisco kinetics. The present study characterizes the kinetic properties of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) from 28 terrestrial plant species, representing different phylogenetic lineages, environmental adaptations and photosynthetic mechanisms.
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