6) Acid Base Catalysis-Mandelate racemase, as shown, catalyzes the racemization

Question

6) Acid Base Catalysis-Mandelate racemase, as shown, catalyzes the racemization of mandelate. Atrolactate is a competitive inhibitor of the enzyme. The picture below shows (S)-atrolactate bound at the active site of the enzyme (PDB ID = 1mdr if you want to explore this on your own). The active site also contains an Mg** (green). Some observations: ? If His297 is replaced in a site-directed mutation by a Gin, the enzyme no longer catalyzes the racemization of the R-mandelate, but still recemizes the S-. ? On the otter hand, if the Lys166 is replaced by an Ala, the R-is still recemized, but the S- is not. Write a mechanism for the non-enzymatic recemization in basic aqueous solution: can you suggest a reason why this recemization is quite slow? Why does atrolactate inhibit the enzyme? Explain the results of the site-directed mutations.

Explanation / Answer

the racemization is slow because the formation of a di anion is not favored (excess of negative charge) and that hydrogen linked to carbone is very few acidic.

b)because it is very similar in structure such that the intermolecular interactions are almost the same. That cause that atrolactate acts as inhibidor blocking the active site.

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