95. You are examining the effects of a mutation in the proximal histidine of a h

Question

95. You are examining the effects of a mutation in the proximal histidine of a heme- containing protein. This mutation has changed the histidine into an alanine. Based on your knowledge of the role of heme in hemoglobin and how it is coordinated in the protein, what is the MOST likely effect of the mutation? A) Heme will no longer be bound in the protein. B) The iron in heme will be fully coordinated. C) The iron in heme will have two uncoordinated bonds. D) The heme will be able to bind to O2 more effectively than it wil to CO. E) There will be no effect on the protein due to this mutation.

Explanation / Answer

A) Heme will no longer be bound in the protein.

proximal His binds the heme iron to hold it in place. If it were replaced by Ala, the iron might not be bound as tightly. And distal His stabilizes the bound O2 molecule by hydrogen-bonding interactions.

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