Carbon fixation is the process by which CO2 is converted from a gas into
biomass. The Calvin Benson Bassham (CBB) cycle is the dominant carbon fixation
pathway on earth, driving >99.5% of the ~120 billion tons of carbon that are
"fixed" as sugar, by plants, algae and cyanobacteria. The carboxylase enzyme in
the CBB, ribulose-1,5-bisphosphate carboxylase/oxygenase (rubisco), fixes one
CO2 molecule per turn of the cycle. Despite being critical to the assimilation
of carbon, rubisco's kinetic rate is not very fast and it is a bottleneck in
flux through the pathway. This presents a paradox - why hasn't rubisco evolved
to be a better catalyst? Many hypothesize that the catalytic mechanism of
rubisco is subject to one or more trade-offs, and that rubisco variants have
been optimized for their native physiological environment. Here we review the
evolution and biochemistry of rubisco through the lens of structure and
mechanism in order to understand what trade-offs limit its improvement. We also
review the many attempts to improve rubisco itself and, thereby, promote plant
growth
