Question

Consider a protein in which a negatively charged glutamic acid side chain (pKa=4.2) makes a salt bridge (ion-ion interaction) with a positively charged histidine side chain (pKa=6.5).

Part A. Do you predict that this salt bridge will become stronger, become weaker, or be unaffected as pH increases from pH=6.9 to pH=7.5?

Answer 1

B. The salt bridge will become weaker.

• At pH=6.9, glutamic acid will carry a negative charge. At lower value of pH such as at pH=3 the side chain in the glutamic acid will become fully ionized.
• In case of Histidine (His) side chain, it  will carry a charge grater than +0.5.
• pH=pKa, the charge on His will be 0.5. Since pH=6.9 above its pka, So it will carry less positive charge and thus become more deprotonated.
• Further on increasing the pH, glutamic acid side chain will still carry -1 i.e. negative charge, and the charge on Histidine will decrease.

Therefore, the salt bridge will become weaker, so option B is correct.

Find more information about "Salt bridge" here:

brainly.com/question/18066138