Rubisco carboxylase/oxygenase: From the enzyme to the globe: A gas exchange perspective

Rubisco is the primary carboxylase of the photosynthetic process, the most abundant enzyme in the biosphere, and also one of the best-characterized enzymes. Rubisco also functions as an oxygenase, a discovery made 50 years ago by Bill Ogren. Carboxylation of ribulose bisphosphate (RuBP) is the first step of the photosynthetic carbon reduction cycle and leads to the assimilation of CO2, whereas the oxygenase activity necessitates the recycling of phosphoglycolate through the photorespiratory carbon oxidation cycle with concomitant loss of CO2. Since the discovery of Rubisco’s dual function, the biochemical properties of Rubisco have underpinned the mechanistic mathematical models of photosynthetic CO2 fixation which link Rubisco kinetic properties to gas exchange of leaves. This has allowed assessments of global CO2 exchange and predictions of how Rubisco has and will shape the environmental responses of crop and global photosynthesis in future climates. Rubisco’s biochemical properties, including its slow catalytic turnover and poor affinity for CO2, constrain crop growth and therefore improving its activity and regulation and minimising photorespiration are key targets for crop improvement.