Question

Please choose the true statement such that an ionic salt bridge can be formed between the side chains of the amino acids listed at the stated pH

a.Arginine and Histidine, at pH 10

b.Histidine and Aspartate, at pH 3

c.Glutamine and Histidine, at pH 8

d.Proline and Lysine at pH 7

e.None of the above can form a salt bridge at these described pH value

Answer 1

Histidine and Aspartate, at pH 3.

One of the salt bridge, between histidine and aspartate, does not form until there is an proton added to histidine. Under conditions of low pH, the histidine gets protonated to allow then the formation of the salt bridge and thus, a conformational change that stabilizes the T-state, lower its affinity for oxygen.

Most common Salt bridges iniproteins:

In proteins, salt bridges most often occur between amino acid side-chains with opposite positive or negative full-electron charges, namely, at neutral pH, Glu- or Asp- vs. Arg+ or Lys+.