Figure 7.
The basicity of Lys218 can be modulated by the active site environment. A, The influence of the adjacent Lys217 prevents Lys218 from becoming protonated by solvent when the active site is vacant and also prevents Lys218 from deprotonating KH2. B, When a glutamate (Glu) substrate enters the active site, any water present is displaced and excluded, and Glu interacts with Lys217, removing its influence on Lys218. The inherent basicity of Lys218 is then restored so that KH2 deprotonation takes place.