Proton-collecting antennae

The surface of the matrix side of cytochrome oxidase contains histidine and aspartate side chains close together. It has been suggested that they form a proton collecting antenna that contains groups basic enough to extract protons from the buffered matrix and guide them to a proton conduction pathway.154 Calcium ions also affect proton flow.153a b We will return to this topic in Section C,3 (p. 1040). 

Fig. 8.3. FCS Proton exchange kinetics measurements at biological membranes, (a) Principal design of experiment. Liposomes were labeled with one FITC fluo-rophore undergoing fluorescence fluctuations due to protonation/deprotonation. (b) Collection of FCS curves of the vesicles at different pH. The FCS curves reflect singlet-triplet transitions in the microsecond time range, protonation kinetics in the 10-100 ps time range and translational diffusion in the milliseconds time range. Inset measured protonation relaxation rates vs. proton concentration, (c) Principle of the proton collecting antenna effect...

Clusters of nearby sites on a protein can serve as highly proton-reactive domains that fulfill special mechanistic roles, like the proton-collecting antenna of the bacteriorhodopsin [25]. For the most recent review see Ref. [26]. 

The proton-collecting antenna was first identified in studies carried out with the ground state form of the protein, which is a resting configuration. To establish the... 

There is a strong resemblance between the mechanism of ion motion next to the protein and the proton-collecting antenna reported for bacteriorhodopsin [78, 79] or cytochrome c oxidase [2]. These domains consist of a cluster of carboxylates that function as proton binding sites. The protonation on any carboxylate of the cluster leads to rapid proton exchange reactions that finally deliver the proton to the immediate vicinity of the proton-conducting channel of the protein. 

Pumping mechanism, cytochrome c oxidase basic physical principle, 79—80 Coulomb machine gun, 80 le/lH-t pumping ratio, 78 membrane potential, 83—84 pK quantum mechanics/molecular mechanics calculations, 84 proton collecting antenna and proton conducting channels, 83 proton loading site (PLS), 80, 82—83 pump element, heme a, 78 water chains, 82... 

The interesting issue of proton collection at the protein surface is not addressed here, but it does appear that proton antennae are designed surface features of several proton translocating proteins, including the bacterial RC (Adelroth et al., 2001), cytochrome oxidase (Marantz el at, 1998), and bR (Checover et al., 1997). 

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