Chemistry 4202 Name
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Homework 3
20 points
1. A competitive inhibitor of an enzyme:
A. increases KM without affecting Vmax.
B. decreases KM without affecting Vmax.
C. increases Vmax without affecting KM.
D. decreases both KM and Vmax.
2. The presence of a noncompetitive inhibitor:
A. leads to both an increase in the Vmax of a reaction and an increase in the KM.
B. leads to a decrease in the observed Vmax.
C. leads to a decrease in KM and Vmax.
D. leads to an increase in KM without affecting Vmax.
3. Sulfonamides (sulfa drugs) such as sulfanilamide are antibacterial drugs that
inhibit the enzyme dihydropteroate synthase (DS) that is required for the
synthesis of folic acid in bacteria.
(a) Draw the structure of sulfanilamide.
(b) Draw the structure of para-aminobenzoic acid (PABA).
(c) If PABA is a substrate for DS, what type of inhibition can be predicted for the
bacterial synthase enzyme in the presence of sulfonamides?
4. On the same graph, plot 1/v0 versus 1/[S] for a typical enzyme reaction (a) in the
absence of an inhibitor, (b) in the presence of a competitive inhibitor, (c) in the
presence of an uncompetitive inhibitor, and (d) in the presence of a
noncompetitive inhibitor.
5. The therapeutic anti-inflammatory effects of aspirin arise from its inhibition of the
enzyme cyclooxygenase-2 (Cox-2, also known as PGH2 synthase), which is involved in
the synthesis of prostaglandins, mediators of inflammation, pain, and fever. Research
the mechanism of inhibition and answer the following questions.
(a) Briefly explain the mechanism of inhibition. What type of inhibition is it?
(b) Aspirin can also inhibit a related intestinal enzyme cyclooxygenase-1 (Cox-1).
What side effects can result from the inhibition of this enzyme? Why?
6. Consider the following data for an enzyme-catalyzed hydrolysis reaction in the
absence and presence of an inhibitor I:
[Substrate] (mM) v0 (mM/min) v0 with I present
(mM/min)
0.5 0.81 0.42
0.67 0.95 0.53
1.0 1.25 0.71
2.0 1.61 1.08
