Fig. 3.

Rubisco catalysis rate for carboxylation (v_c, blue) and oxygenation (v_o, red) under different conditions of deuteration, using the enzyme from tobacco (A and B) or R. rubrum (C and D). Assays were carried out using ordinary water (H₂O) or deuterated water (D₂O, 96%) as a solvent, with ordinary (i.e., deuterium at natural abundance) or deuterated (99% D at the H3 atom position) ribulose 1,5-bisphosphate (RuBP). Carboxylation was assayed at 45 µM (tobacco) and 150 µM (R. rubrum) dissolved CO₂, and oxygenation at 200 µM dissolved O₂. Data are mean and SD of n = 4 replicates. Letters stand for statistical classes: when two bars harbor distinct letters, it indicates that the values are statistically different (ANOVA, P < 0.01). Numbers above bars indicate the average H/D isotope effect (with reference to H₂O + h-RuBP).