Deck 8: Mechanisms and Inhibitors

Question 1

Use the following to answer questions
Choose the correct answer from the list below. Not all of the answers will be used.
a) hydrolysis
b) affinity label
c) tyrosinase
d) chymotrypsin
e) pepsin
f) noncompetitive
g) uncompetitive
h) heterotropic
i) approximation and orientation
j) acid-base
h) competitive
____________: The type of catalysis in which two substrates are brought into close proximity.

Answer 1

j

Question 2

The mechanism of chymotrypsin involves the formation of an unstable ________________-shaped intermediate that is stabilized by the oxyanion hole.

Answer 2

tetrahedral

Question 3

Use the following to answer questions
Choose the correct answer from the list below. Not all of the answers will be used.
a) hydrolysis
b) affinity label
c) tyrosinase
d) chymotrypsin
e) pepsin
f) noncompetitive
g) uncompetitive
h) heterotropic
i) approximation and orientation
j) acid-base
h) competitive
____________: A molecule that is also known as a substrate analog.

Answer 3

b

Question 4

A ________________ inhibitor binds irreversibly to the active site of an enzyme.

Question 5

The ________________ stabilizes the tetrahedral intermediate of the hydrolysis of a peptide bond by chymotrypsin.

Question 6

Use the following to answer questions
Choose the correct answer from the list below. Not all of the answers will be used.
a) hydrolysis
b) affinity label
c) tyrosinase
d) chymotrypsin
e) pepsin
f) noncompetitive
g) uncompetitive
h) heterotropic
i) approximation and orientation
j) acid-base
h) competitive
____________: The inhibitor which binds only to the ES complex and lowers the Vmax and KM.

Question 7

In conducting an experiment with a new drug, you find that regardless of the concentration of substrate, the drug is able to inhibit the enzyme activity. You are likely to not have a(n) ________________ type of inhibitor.

Question 8

The straight-line kinetic plot of 1/V0 versus 1/S is called a ________________.

Question 9

Use the following to answer questions
Choose the correct answer from the list below. Not all of the answers will be used.
a) hydrolysis
b) affinity label
c) tyrosinase
d) chymotrypsin
e) pepsin
f) noncompetitive
g) uncompetitive
h) heterotropic
i) approximation and orientation
j) acid-base
h) competitive
____________: An enzyme that is part of a pigment formation pathway and has a low optimum temperature.

Question 10

An enzyme catalyst mechanism that uses a metal cation to stabilize a negative charge in the active site is ________________.

Question 11

A ________________ catalytic mechanism that forces two substrates into an appropriate three-dimensional arrangement for the reaction to occur.

Question 12

Use the following to answer questions
Choose the correct answer from the list below. Not all of the answers will be used.
a) hydrolysis
b) affinity label
c) tyrosinase
d) chymotrypsin
e) pepsin
f) noncompetitive
g) uncompetitive
h) heterotropic
i) approximation and orientation
j) acid-base
h) competitive
____________: A type of enzyme inhibitor where KM is unaltered.

Question 13

Use the following to answer questions
Choose the correct answer from the list below. Not all of the answers will be used.
a) hydrolysis
b) affinity label
c) tyrosinase
d) chymotrypsin
e) pepsin
f) noncompetitive
g) uncompetitive
h) heterotropic
i) approximation and orientation
j) acid-base
h) competitive
____________: The enzyme inhibition that can be overcome by increasing the concentration of substrate.

Question 14

An uncompetitive inhibitor will have two ________________ lines on a double-reciprocal plot.

Question 15

The antibiotic penicillin is an example of a(n) ________________ inhibitor.

Question 16

Use the following to answer questions
Choose the correct answer from the list below. Not all of the answers will be used.
a) hydrolysis
b) affinity label
c) tyrosinase
d) chymotrypsin
e) pepsin
f) noncompetitive
g) uncompetitive
h) heterotropic
i) approximation and orientation
j) acid-base
h) competitive
____________: The type of reaction catalyzed by proteases.

Question 17

Use the following to answer questions
Choose the correct answer from the list below. Not all of the answers will be used.
a) hydrolysis
b) affinity label
c) tyrosinase
d) chymotrypsin
e) pepsin
f) noncompetitive
g) uncompetitive
h) heterotropic
i) approximation and orientation
j) acid-base
h) competitive
____________: A type of catalysis where the proton donor is not water.

Question 18

A(n) ________________ inhibitor has a structure similar to the substrate and reversibly binds to the active site of the enzyme.

Question 19

Use the following to answer questions
Choose the correct answer from the list below. Not all of the answers will be used.
a) hydrolysis
b) affinity label
c) tyrosinase
d) chymotrypsin
e) pepsin
f) noncompetitive
g) uncompetitive
h) heterotropic
i) approximation and orientation
j) acid-base
h) competitive
____________: A protease enzyme with a low pH optimum.

Question 20

Use the following to answer questions
Choose the correct answer from the list below. Not all of the answers will be used.
a) hydrolysis
b) affinity label
c) tyrosinase
d) chymotrypsin
e) pepsin
f) noncompetitive
g) uncompetitive
h) heterotropic
i) approximation and orientation
j) acid-base
h) competitive
____________: An enzyme that temporarily undergoes covalent catalysis as part of its mechanism.

Question 21

In this type of inhibition, the inhibitor can only bind to the ES complex to form an ESI complex.

A) competitive
B) noncompetitive
C) irreversible
D) uncompetitive
E) None of the above.

Question 22

How can covalent modification be used to determine the mechanism of action of an enzyme?

Question 23

What caused a "burst" of activity followed by a steady-state reaction when chymotrypsin was studied by stop-flow techniques?

Question 24

How are the types of inhibition kinetically distinguishable?

Question 25

Where does cleavage of the scissile bond by chymotrypsin occur?

A) between a his and a ser amino acid
B) on the N-terminal side of a phe or trp residue
C) on the C-terminal side of a phe or trp residue
D) at the N-terminal amino acid
E) on the C-terminal side of an arg or lys amino acid

Question 26

Which type(s) of inhibition can be reversed?

A) competitive
B) noncompetitive
C) uncompetitive
D) All of the above.
E) None of the above.

Question 27

Which amino acids in chymotrypsin are found in the active site and are participants in substrate cleavage?

A) his, ser, asp
B) his, ser
C) asp, lys
D) lys, arg
E) his, ser, arg

Question 28

What is the difference between KM and KM app?

Question 29

The metal most commonly found at the active site of metalloproteases is:

A) zinc.
B) calcium.
C) selenium.
D) magnesium.
E) sodium.

Question 30

There is a key difference between an enzyme that uses a covalent catalysis mechanism and one that uses other catalytic strategies. What is this key difference?

Question 31

A protein that is optimally active at neutral pH is likely to have which in the active site?

A) the side chains of aspartate and glutamine
B) two histidine amino acid side chains
C) a glycine amino acid
D) one or more carboxyl groups
E) two amino groups

Question 32

Binding of a water molecule to the zinc ion induces:

A) a hydronium ion to form.
B) a large conformation change in the binding site.
C) ionization of a his residue, which functions as a strong nucleophile.
D) a lowered pKa for water, which leads to the formation of a zinc-bound hydroxide ion.
E) an altered KM value.

Question 33

Why are substrate analogs used to monitor enzyme activity?

Question 34

What is an affinity label?

Question 35

What factors should an enzymologist consider when designing an enzyme assay?

Question 36

What is the challenge for a protease to facilitate hydrolysis of a peptide bond?

Question 37

Which of the following curves (no inhibitor, inhibitor 1, or inhibitor 2) represents the rate of reaction versus substrate concentration for a competitive and an uncompetitive inhibitor? Draw the double-reciprocal plot for each case.

Question 38

Designing drugs to inhibit enzymes is a large part of pharmaceutical research. What are some of the enzymatic features that would be important?

Question 39

What conclusion can be drawn concerning an inhibitor if the KM is the same in the presence and absence of the inhibitor?

A) The inhibitor binds to the substrate.
B) The inhibitor has a structure that is not very similar to the substrate.
C) The inhibitor forms a reversible covalent bond with the enzyme.
D) The inhibitor binds to the same active site as the substrate.
E) The Vmax is larger in the presence of the inhibitor.

Question 40

How is specificity determined by chymotrypsin?

A) by an interaction of the active site amino acids with the substrate
B) by a binding of the N-terminus amino acid at the active site
C) by a covalent binding of a his residue to the substrate
D) by a conformational change upon the binding of substrate
E) by a binding of the proper amino acid into a deep pocket on the enzyme

Question 41

How is the enzyme chymotrypsin bind and hydrolyze its substrate? How does this differ from other proteases?

Question 42

A site-directed mutagenesis converting histidine-57 of chymotrypsin to a lysine results in an inactive enzyme even though lysine has an amino group in its side chain. Describe why the scientist may have thought this result surprising and why it wasn't.

Question 43

Bacteria that become penicillin resistant express an enzyme called β-lactamase. This enzyme hydrolyses the lactam ring on penicillin. Suggest a reason why this protein allows cells to grow in the presence of penicillin.

Question 44

Draw and describe the reaction pathway for a noncompetitive inhibitor.

Question 45

Describe the mechanism for the proteolysis catalyzed by chymotrypsin.

Question 46

The initial reaction kinetics of some enzymes results in a quick burst of product in a short period of time, followed by a slower but sustained increase in product formation over time. What does this type of kinetic response tell an enzymologist about the mechanism of the catalysis?

Question 47

You measure the initial velocity of an enzyme in the absence and presence of two inhibitors. In each case, the inhibitor is at 10 µM. Shown in the table below is the primary data for all three cases. Construct a Lineweaver-Burk plot for each case. Calculate the KM and Vmax for each case, both graphically and mathematically. Determine the mechanism for each inhibitor and where each will interact on the enzyme.
Initial Velocity (µmol/ml min)
Enzyme Enzyme Enzyme
[S] mM Alone + Inhibitor 1 + Inhibitor 2
0.33 1.65 1.05 0.79
0.50 2.13 1.43 1.02
1.00 2.99 2.22 1.43
2.00 3.72 3.08 1.79
5.00 4.00 3.80 2.00

Question 48

What are group-specific reagents?