Figure 9.

The active site and protonation states of glutamate residues with backbone carbonyl O atoms (PDB entry 6kk8, H/D exchanged; Yamada et al., 2019 ▸). 2F _o − F _c NSLD map (σ = 1.00) is displayed as a blue mesh; H and D atoms are displayed in white and turquoise, respectively. (a) Manganese catalase active site with the bridging O atoms coordinated to the two manganese cofactors. Bridging atoms O₁₀₀₄ and O₁₀₀₅ have alternate conformations, which are shown in red and pale red. (b) Single protonation of Glu167 forming a hydrogen bond to the Ala279 carbonyl group oxygen. (c) Single protonation of Glu280 forming a hydrogen bond to the Phe116 carbonyl group oxygen.