Rubisco activase operates as a chaperone enzyme responsible for maintaining the catalytic competency of Ribulose 1,5-bisphophate carboxylase oxygenase (Rubsico) in plants. Rubisco is the first step in the Calvin-Benson cycle which is the major entry point of atmospheric CO₂ into the biome. Rubisco is notoriously inefficient, rapidly self-inactivating in physiological conditions. Rubisco activase uses the power released from the hydrolysis of ATP to power conformational change in Rubisco and reactivate Rubsico.

Rubisco activase has been shown to form a large range of species in solution, however little has been done to relate the size of oligomeric species and physiological activity. Here we present data from a range of techniques including analytical ultracentrifugation (AUC), static light scattering (SLS) and small angle X-ray scattering (SAXS) combined with activity assays to show a very strong relationship between oligomeric size and activity. Our results suggest that small oligomers comprising around 3 subunits are enough to attain full activity and we believe this is the first case of this for enzymes from this family. Recent work with a number of mutant Rubisco activase has allowed to us to probe the effect of ATP and ADP on oligomeric state.