Exercise on Enzyme Catalysis |
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1. These diagrams are my versions of the mechanism of action of chymotrypsin. The first diagram is for part g.
In the next set of diagrams:
a. Identify the diagram that shows only the substrate (no active site), the aromatic
side chain, and the peptide bond that will be hydrolyzed. Identify the part of the
substrate that will be product 1 and the part that will be product 2.
b. Identify the diagram that shows only the active site (no substrate), the catalytic
triad, and the oxyanion hole. The enzyme backbone is labeled E.
c. Identify the diagram that shows the modified enzyme after release of product 1.
d. Identify the diagram that shows substrate 1 in the active site before formation of
a tetrahedral intermediate.
e. Identify the diagram that shows substrate 2 in the active site before formation of
a tetrahedral intermediate.
f. Cut out the diagrams, put them in order, and add arrows to show the movement
of electrons. Color or highlight the protons that are exchanged.
g. The diagram below shows the active site with a tetrahedral intermediate. Identify
the catalytic triad, the oxyanion hole, the part of the intermediate that was
substrate 1, and the part that was substrate 2.
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2. Enolase catalyzes the reversible conversion of 2-phosphoglycerate to PEP + H2O:
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a. Identify the H and OH that are removed from 2-phosphoglycerate to form water.
b. Draw the structure of glycerate (no phosphate attached).
3. The diagrams below represent (A) the active site of enolase without substrate;
(B) the active site + substrate; (C) the active site with a transition state;
(D) the active site + product.
a. Identify each phase of the reaction.
b. Color the protons that are exchanged.
c. Add arrows to the diagrams to show the movement of electrons.
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4. Name the enzyme, substrate(s), and product(s) of the reaction shown below.
Name the mechanisms of enzyme catalysis used.
Color the protons to show their exchange.
5. The reaction catalyzed by lactate dehydrogenase is shown below: 
The coenzyme NAD+ donates or accepts H– (= H+ + 2 e-).
a. Identify the 2 H's removed from lactate.
b. What must be included for the reaction to be complete?
6. The active site of lactate dehydrogenase is shown with lactate and with pyruvate.
a. What is the function of Arg 171 in the active site?
b. What is the function of His 195 in the active site?
c. Based upon these diagrams, what mechanism(s) of enzyme catalysis does lactate
dehydrogenase use?
d. Does the enzyme form a ternary complex or use a ping pong mechanism?
