Many enzymes catalyze reactions that are similar to reactions we might use for organic synthesis. Enzymes tend to be stereospecific in their reactions, and asymmetric induction is common. The following reaction, part of the tricarboxylic acid cycle of cell respiration, resembles a reaction we might use in the laboratory; however, the enzyme-catalyzed reaction gives only the (S) enantiomer of the product, malic acid.

(a) What type of reaction does fumarase catalyze?
(b) Is fumaric acid chiral? Is malic acid chiral? In the enzyme-catalyzed reaction, is the product (malic acid) optically active?
(c) If we could run the preceding reaction in the laboratory using sulfuric acid as the catalyst, would the product (malic acid) be optically active?
(d) Do you expect the fumarase enzyme to be a chiral molecule?
(e) When the enzyme-catalyzed reaction takes place in D2O the only product is the stereoisomer just pictured. No enantiomer or diastereomer of this compound is formed. Is the enzyme-catalyzed reaction a syn or anti addition?
(f) Assume we found conditions to convert fumaric acid to deuterated malic acid using hydroboration with followed by oxidation withD2O2 and NaOD. Use Fischer projections to show the stereoisomer(s) of deuterated malic acid you would expect to be formed.

Transcribed Image Text:

H COOH HO COOH COOD DO H umarase H20. pH 7.4 CH,COOH (S)-malic acid HOOC COOD fumaric acid product in D,O