- Isozymes for a given reaction
have
different substrate specificities.
have
identical affinities for the same substrate.
bind
at least two different substrates.
exhibit
different electrophoretic mobilities.
contain
similar ratios of different polypeptide chains.
- Which one of the following proteolytic enzymes is activated
by acid hydrolysis of the proenzyme form?
trypsin
chymotrypsin
elastase
pepsin
carboxypeptidase
- All the following assumptions apply to Michaelis-Menten kinetic
analyses of enzyme action EXCEPT
the
total enzyme concentration studied at each substrate concentration
is fixed in analysis of enzyme kinetics.
formation
of enzyme-substrate complex does not appreciably decrease the
concentration of substrate.
Km
decreases with competitive inhibition.
maximal
velocity is reached when the enzyme-substrate complex is equal
to the total concentration of enzyme present.
the
initial reaction velocity should be measured because most of
the substrate has not been converted to product.
Refer to the following graph when answering questions
4 - 7.
- The value of Km for the enzyme depicted by curve
A is
0.5
mM.
1
mM.
2
mM.
1
µmol min-1 mg-1.
10
µmol min-1 mg-1.
- The value of Vmax for the enzyme depicted by curve
A is
0.1
µmol min-1 mg-1.
1
µmol min-1 mg-1.
10
µmol min-1 mg-1.
0.5
µM.
2
mM.
- Curve B depicts the effect of an inhibitor on the system
described by curve A. This inhibitor
is
a competitive inhibitor.
is
a noncompetitive inhibitor.
increases
the Vmax.
decreases
the Km.
- Curve C depicts the effect of a different inhibitor of the
system described by curve A. This second inhibitor
is
a competitive inhibitor.
is
a noncompetitive inhibitor.
increases
the Vmax.
decreases
the Km.
Refer to the following graph when answering questions
8 and 9.
| The plot represents the relationship between
substrate concentration and velocity for a single enzyme in the
absence (curve x) and presence (curve y) of a compound that binds
allosterically to the enzyme. |
- In the presence of the allosteric compound
Km
and Vmax both increase.
Km
and Vmax both decrease.
Km
increases and Vmax decreases.
Km
decreases and Vmax increases.
Km
decreases and Vmax stays the same.
- The allosteric compound is
a
competitive inhibitor.
a
noncompetitive inhibitor.
an
irreversible inhibitor.
an
activator.
isocitrate + NAD+ Æ
a-ketoglutarate + CO2 +
NADH + H+
- Isocitrate dehydrogenase catalyzes the reaction given above.
The curves illustrated above are obtained when the initial velocity
(v) of the reaction is plotted against isocitrate concentration
in the presence of various levels of ADP and excess NAD+.
Which of the following statements about this system is correct?
Isocitrate
dehydrogenase exhibits simple Michaelis-Menten kinetics in the
absence of ADP.
ADP
increases the Km of the enzyme for isocitrate.
ADP
increases the Vmax of the enzyme.
ADP
activates the enzyme.