Enzyme Kinetics- Lectures 9-11 Flashcards
What is a non-competitive inhibitor?
a compound that does not bind at the substrate binding site, so it cannot be displaced by increasing the concentrations of S
What is a competitive inhibitor?
a compound that binds at the substrate binding site due to its structural similarity that cannot be altered by the enzyme and competes for access to the site with the substrate; it can be overcome with greater [S}
What would a Lineweaver- Burk plot of a non-competitive inhibitor look like in comparison to a normal one?
Vmax would be reduced –> Y intercept would be higher
Km is unchanged –> X intercept (1/Km) would be the same
How would you calculate the extent of the change in Vmax when a non-competitive inhibitor is added?
Vmax’ = (Vmax) / [ 1 + ( [I] / Ki) ]
What would a Lineweaver-Burk plot of a competitive inhibitor look like in comparison to a normal one?
Vmax is unchanged –> Y intercept (1/Vmax) is unchanged
Km is increased –> X intercept moves to the R on the graph
What is an uncompetitive inhibitor?
a compound that binds an enzyme after its substrate is bound that stabilizes the enzyme/substrate complex and slows the dissociation of the substrate from the enzyme and production of product
What would a Lineweaver-Burk plot of an uncompetitive inhibitor look like in comparison to a normal one?
Vmax decreases –> Y intercept is higher
Km is decreased –> X intercept moves to the L
What is an irreversible inhibitor?
compounds that form a covalent and essentially irreversible bond with the enzyme, reducing the
What would a Lineweaver-Burk plot of an irreversible inhibitor look like in comparison to a normal one?
just like a non-competitive inhibitor:
Vmax would be reduced –> Y intercept would be higher
Km is unchanged –> X intercept (1/Km) would be the same
When is a reaction considered first order?
in the first (linear) region of a Michaelis-Menton plot where the initial rate is directly proportional to [S]
When is a reaction considered zero order?
in the second (exponential) region of a Michaelis-Menton plot where [S] is high and V0 becomes constant –> rate is independent of [S]
What are two reasons why one enzyme’s (Enzyme B) Vmax may be higher than another’s (Enzyme A) for the same substrate?
enzyme B may have more than one active site for this substance possibly on different subunits of a multimeric enzyme)
Enzyme B could operate more effectively using a single active site
What is the Michaelis-Menten equation?
Vmax [S]
V0= —————–
Km + [S]
What is the Lineweaver-Burke equation?
1 Km 1 1
—- = ———- x —- + —–
V0 Vmax [S] Vmax
What is IC50 and how is it calculated?
measure of an inhibitor’s potency; the inhibitor concentration that produces half of the maximal effect;
IC50 = Ki ( 1 + [S]/Km)
