A mutation that changes an Alanine residue in the interior of a protein to relin

Question

A mutation that changes an Alanine residue in the interior of a protein to reline leads to loss of activity However, activity is regained when a second mutation at a different position changes an isoleucine into glycine what do you think happened to restore activity. Reduced ribonuclease was reoxidized first by itself second by reoxidizing in presence of 8 M urea and then removing area by dialysis. Ribonuclease reoxidized the latter way had only 1% enzymatic axial activity why did the enzyme reoxidize differently in presence and absence of urea

Explanation / Answer

Answer:

8. A mutation that changes an alanine residue in the interior of a protein to valine is found to lead a loss of activity. Thus the first mutation destroys activity, the protein must take a different shape because valine occupies more space than alanine does, assuming that this residue lies in the closely packed interior. The activity is regained when a second mutation at a different position changes an isoleucine residue to a glycine. The second mutation restores activity because glycine is smaller than isoleucine resulting the compensatory reduction of volume.

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