Figure 8.

A power-law relationship between k_cat,C/K_C and k_cat,O/K_O can be explained by an active site that fluctuates between “reactive” and “unreactive” states. (A) In this model, CO₂ and O₂ react with bound RuBP only when the enzyme is in the reactive state, which has an occupancy φ. (B) φ can vary between related enzymes. In the reactive state, CO₂ and O₂ react with the bound RuBP with intrinsic reactivities ΔG*_1,C and ΔG*_1,O that do not vary between related Rubiscos. If the difference in intrinsic reactivities (ΔG*_1,O – ΔG*_1,C) is constant, we derive a power-law relationship between k_cat,C/K_C and k_cat,O/K_O with an exponent of 1.0. This relationship requires a constant S_C/O (Supporting Information).