1.A mutant form of LDH in which Arg109 is replaced with Gln shows only 5% of the pyruvate binding and 0.07% of the activity of wild-type enzyme. Provide a plausible explanation for the effects of this mutation.

It is a replacement that has an important effect on protein function because Arg and Gln are residues with different chemical properties.

Explanation:

In this case, Arginine (Arg) is a basic and positively charged residue, while Glutamine (Gln) is an uncharged (neutral) amino acid. Non-conservative substitutions like that are generally expected to have deleterious effects and they are generally removed by natural selection. Moreover, Arg is also a target for phosphorylation, which is the most important posttranslational modification. Phosphorylation is known to be capable of causing the activation of different proteins, especially kinases, and, therefore, the mutation at Arg109 might also inactivate the active site of this protein.

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