Enzyme Kinetics and Inhibition Flashcards
How does enzyme regulation often take place?
Through inhibition (stops enzyme from working properly)
What is an inhibitor?
It is a substance that interacts with an enzyme in a way that prevents it from catalyzing the reaction that it normally would.
Is inhibition reversible?
Yes, well almost always.
How does an inhibitor bind to enzyme?
Through non-covalent interactions.
What are irreversible inhibitors which form covalent bonds with enzymes called? (Not common on MCAT)
Suicide Inhibitors
On the level of individual molecules, can inhibitors completely block an enzyme from functioning?
Yes
In real-life, what happens when we apply inhibitors?
We are only going to interfere with some of the reaction. Applying the inhibitor will just slow down the reaction not completely stop it.
What does the Michaelis-Menten Model tell us?
It underpins everything that we say about enzyme kinetics and inhibition.
What does it mean for enzymes to be saturated?
It means that all molecules of an enzyme are occupied. This is the point that the enzyme-catalyzed reaction is at its maximum rate (Vmax).
What does Vmax stand for?
The maximum rate of reaction
It is one of the two key variables in Michaelis-Menten Kinetics
What does Km stand for?
It is the concentration of substrate that corresponds to half of Vmax. It measures how readily an enzyme interacts with its substrate. Is is the [S] at 1/2 Vmax
Equation for finding velocity in Michaelis-Menten Model
V= (Vmax x [S]) / (Km + [S])
What does a high Km mean?
Enzyme has low affinity for its substrate
What does a low Km mean?
Enzyme has high affinity for its substrate
Describe a Michaelis-Menten Plot.
It has reaction rate or V on Y-axis and it has substrate concentration on X-axis.
It has a fixed concentration of enzyme
Graph has hyperbolic shape
Never reaches Vmax (forms asymptote)
What do Michaelis-Menten Curves show?
They show how changes in substrate concentrations affect reaction speed, given a fixed quantity of enzyme.
Why does reducing enzyme concentration also decrease the Vmax of the enzyme-catalyzed reaction?
Because there are fewer enzyme molecules available to catalyze the reaction.
Describe the Lineweaver-Burk Plot
Double-reciprical transformations of the Michaelis-Menten Plots. It assigns very specific graphical coordinates to the important parameters of Km and Vmax
X-intercept = -1/Km
Y-intercept = 1/Vmax
What does increasing Vmax do to the Lineweaver-Burk Plot?
Makes Y-intercept smaller
What does decreasing Vmax do to the Lineweaver-Burk Plot?
Makes Y-intercept larger
What does increasing Km do to the Lineweaver-Burk Plot?
Makes X-intercept have a greater value (brings x-intercept closer to origin)
What does decreasing Km do to the Lineweaver-Burk Plot?
Makes X-intercept have a lesser value (moves x-intercept further away from origin)
What are the four key types of reversible inhibition?
Competitive
Noncompetitive
Uncompetitive
Mixed
What are competitive inhibitors? What do they do to the MMP and LBP
They compete with the substrate for the active site.
Vmax = same, Km = up
MMP- hyperbolic line starts below but eventually reaches
uninhibited’s curve’s Vmax.
LBP- y-intercept stays the same
x-intercept moves closer to the origin
So slope gets steeper.
What are noncompetitive inhibitors? What do they do to the MMP and LBP
They interact with enzyme allosterically.
Vmax = decreases, Km = same
MMP- hyperbolic line stays below uninhibited curve the
entire time
LBP- y-intercept increases
x-intercept stays the same
So slope gets steeper.
What are uncompetitive inhibitors? What do they do to the MMP and LBP
They interact with enzyme-substrate complex at an allosteric site and essentially prevent the enzyme from letting go of the substate after it is bound.
Vmax = decreases, Km = down
MMP- hyperbolic line starts higher but then ends below
uninhibited’s curve
LBP- y-intercept increases
x-intercept moves further away from origin
What are mixed inhibitors? What do they do to the MMP and LBP
They either bind to free enzyme at an allosteric site or bind to the enzyme-substrate complex
Vmax = decreases, Km = up if it binds to free enzyme
Km = down if it binds to E-S complex
MMP- hyperbolic line always ends below the uninhibited
curve. But the curve of the graph depends on
binding preference
LBP- y-intercept increases
x-intercept moves closer to the origin if it binds to
free enzyme and further away if it binds to E-S
complex.
What type of inhibitors are substrate analogs?
Competitive inhibitors because they share structural features with the enzymes endogenous substrate, which allows them to bind to the active site of the enzyme.
What does the Michaelis-Menten Plot show?
It shows how changes in the SUBSTRATE concentration affect the speed of the reaction. Enzyme concentration is held constant.
