Figure 4.

Structural changes occurring during proton transfer in (a) the α₂β₂-heterotetramer and (b) the β-monomer. In both panels, the minimum energy reactant structure is shown with green carbon atoms; the α₂β₂-heterotetramer structure after the maximum degree of C1–H1 rotation is shown with yellow carbon atoms in (a), and the β-monomer structure with the corresponding decrease in O2–H1 distance (1.1 Å) is shown with yellow carbon atoms in (b) (see also figure 6).