Pore peripheries

High-resolution images obtained across the PEO layer are shown in Figure 5. Features of amorphous TiOa can be found in area A, The transition from amorphous titania into crystalline rutile is clearly seen in area B, while anatase lattice in area C around the pore periphery is identified. These verify the findings in the SAD analysis. 

If there is a significant resistance to transport of the reactant in the pores, a concentration gradient will exist at steady state, whereby the concentration of the reactant is a maximum at the particle periphery and a minimum at the particle center. The product concentration will be higher at the particle center than at the periphery. The concentration gradients provide the driving force for the transport. 

Conclusions from the reference 28 review article are as follows (1) Several models backed by experiment place S4 near the groove between adjacent subunits, while the MacKinnon group model places S4 near the periphery of the protein (2) lanthanide-based resonance energy transfer (LRET) places two S4 residues in segments across the tetramer from each other at a distance of 45 A (3) a method based on tethered quaternary ammonium pore blockers places the extracellular ends of the SI and S3 helices further away from the ion conduction pore than the S3-S4 linker, arguing that the S4 helix resides... 

Crystallographic studies led to the high-resolution structure of KcsA by Doyle et al. (1998b), an achievement that lent a firm structural foundation to more than three decades of functional work on K+ channels. The crystal structure revealed that KcsA is formed by the association of four subunits, contributing equally to form a water-filled pore. Each subunit has two transmembrane segments, TM1 in the periphery of the complex and TM2 lining the permeation path. Toward the extracellular face of the channel is the selectivity filter, where intimate contact with the permeant ions takes place. 

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