Acid-Base-controlled Molecular Shuttle

Figure 6.7 A chemically controllable molecular shuttle. The macrocydic ring can be switched between the two stations of the dumbbell-shaped component by acid-base inputs.

Fig. 3 A chemically controllable molecular shuttle the macrocyelic ring can be switched between the two stations of the dumbbell-shaped component by base/acid inputs. Additionally, in the deprotonated rotaxane, the ring can be displaced from the bipyridinium station through reduction of such unit. (View this art in color at www.dekker.com.)...

The molecular components of many buffers are too large to reach the active site of carbonic anhydrase. Carbonic anhydrase II has evolved a proton shuttle to allow buffer components to participate in the reaction from solution. The primary component of this shuttle is histidine 64. This residue transfers protons from the zinc-bound water molecule to the protein surface and then to the buffer (Figure 9.30). Thus, catalytic function has been enhanced through the evolution of an apparatus for controlling proton transfer from and to the active site. Because protons participate in many biochemical reactions, the manipulation of the proton inventory within active sites is crucial to the function of many enzymes and explains the prominence of acid-base catalysis. 

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