Amino acid residue carbonyl group

Once the pore is open, K+ ions appear to move outward in single file. Analysis of crystals shows four K+ ions interacting with the backbone carbonyl groups of the amino acid residues that form the ion selectivity filter (Fig. 6-8B). It is thought that two K+ ions occupy sites 1 and 3 (Fig. 6-8B, orange) and then switch to sites 2 and 4 (gray). The K+ ion in site 4 would dissociate into the extracellular space, the K+ ion in site 2 would move to site 3 and another... 

Peptide bonds involving a-amino acid residues have been shown to be in the trans conformation but for Pro-containing and A-methylglycine peptides the bond may be cis or trans. When isomerization of Pro-Pro peptide bond occurs, the a and 6 protons of the pyrrolidine ring change positions with respect to the carbonyl group. ... 

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