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Figure 2
The active site of hCA II at different internal CO2 pressures. (a) 15 atm CO2 hCA II, (b) 7.0 atm CO2 hCA II, (c) 2.5 atm CO2 hCA II, (d) 15 atm CO2 hCA II – 50s, (e) 15 atm CO2 hCA II – 1h. The electron-density (2FoFc) map (in blue) is contoured at 1.3σ, except for W′I in (d), which is contoured at 1.0σ. The intermediate waters WI and W′I are coloured light grey and the entrance-conduit water W′EC1 is coloured cyan for clarity. Note that CO2 is fully bound in the active site in (a) and (b). Concurrent with the decrease in CO2 pressure, the electron density for CO2 fades out in (c) and is eventually replaced by two water molecules in the CO2 binding site (d, e). Note also the dynamic changes reflected by the electron densities of WI, W′I and W1 that take place as the internal CO2 pressure decreases. These events are more explicitly explained in Fig. 4[link].

Volume 5| Part 1| January 2018| Pages 93-102
ISSN: 2052-2525