Figure 6.

Negative power-law correlation between k_cat,C and k_cat,C/K_C is not supported by the extended data set. In the model diagrammed in panel A, CO₂-specific Rubiscos have low barriers to enolization and CO₂ addition (first effective carboxylation barrier ΔG_1,C), but lowering the first effective barrier necessarily increases the second effective barrier (ΔG_2,C), reducing k_cat,C. In this view, stabilizing the first carboxylation TS also enhances selectivity but also slows carboxylation (Figure S2). ΔG_1,C and ΔG_2,C should be negatively correlated, which would manifest as negative power-law correlation between k_cat,C and k_cat,C/K_C under certain assumptions (Supporting Information). (B) The extended data set does not evidence the expected correlation (for Form I enzymes, R = 0.02 and p = 0.8). While previous analyses gave an R of approximately −0.9,⁶ the 95% confidence interval for R now includes 0.0. Restricting our focus to particular physiologies like C₃ plants does not result in the expected correlation.