Enzyme Inhibition Flashcards
What are chemicals that reduce the rate of enzymatic reactions?
Inhibitors
What are two types of enzyme inhibitors?
Irreversible and reversible
What type of inhibitor covalently modifies the active site of the enzyme irreversibly?
Irreversible
What type of inhibitor can be washed out of the solution of enzyme by dialysis?
reversible
What are the different types of reversible inhibitors?
1) Competitive
2) Uncompetitive
3) Non-competitive
What are two different types of non-competitive inhibtors?
pure; mixed
What residue does AchE use to prevent nerve gases and pesticides from getting utilized for catalysuis?
Serine
Which type of inhibition does the inhibitor structure closely resemble the substrate’s structure and competes for the active site of the enzyme with the substrate?
Competitive
Which type of inhibition does the inhibitor reduce the number of enzyme molecules available for the substrate?
Competitive
Which type of inhibition does the inhibitor increase the km but not the overall velocity (vmax does not change)?
Competitive
What is the equation for competitive inhibition?
vo=(Vmax[S])/(alphaKm + [S])
What is the dissociation constant of EI in competitive inhibition?
Ki= [E][I]/[EI]
What is alpha and what is its equation?
the degree of inhibition
alpha = 1 + ([I]/Ki)
In competitive inhibition, the LB-plot slope increases as what increases?
the degree of inhibition (alpha)
What example for competitive inhibition was given in class?
Methotrexate competitively inhibits dihydrofolate reductase (DHFR) (inhibits DNA synthesis)
HIV Protease Inhibitors (HIV Protease cleaves Phe-Pro bond
How do you determine Ki for competitive inhibition?
1) plot I/vo vs 1/[S] (LB-plot) for different Is
2) find the slope of each line produced
3) plot the slope of the lines vs [I]
4) the x-intercept is -Ki (in concentration units)
How do you overcome competitive inhibition?
by increasing the concentration of the substrate [S] Vmax can be attainable
What example of overcoming competitive inhibition was given in class?
methanol or ethylene glycol poisoning, patients are given ethanol
methanol gets converted to formaldehyde instead of acetic acid (ethanol gets converted to acetic acid)
methanol is excreted in the urine if out-competed by ethanol
When this binds to an enzyme it completely distorts the active site rendering the enzyme catalytically innactive. What is it?
An uncompetitive enzyme
In uncompetititve inhibition, the inhibitor affects what but not what?
the catalytic function of the enzyme; the substrate binding
Vmax and km are reduced by the same extent in what type of inhibition?
Uncompetitive
What is the Michaelis-Menton equation for uncompetitive inhibition?
vo=(Vmax[S])/(Km+alpha’[S])
What is the dissociation constant for ESI?
K’i = ([ES][I])/[ESI]
What is the degree of inhibition for uncompetitive inhibition?
alpha’ = 1 + ([I]/K’i)
Does the slope change in uncompetitive inhibition?
No
Can the effect of the uncompetitive inhibitor be abolish by increasing [S]?
No
What was an example of an uncompetitive inhibitor given in class?
Round up- interferes with the synthesis of the aromatic amino acids
How do you find Ki for uncompetitive inhibition?
- plot I/vo vs 1/[S]
- plot the slopes of the lines formed vs [I]
- -K’i = to the x-intercept
What kind of inhibitor can bind to the free enzyme as well as the enzyme/substrate complex and affects both substrate binding and catalysis?
Non-competitive
The non-competitive inhibitor binds to E and ES but may have a greater affinity for what?
one over the other
If the binding affinity of the non-competitive inhibitor to free enzyme equals the binding affinity to the enzyme/substrate complex, the inhibition is considered what?
Pure
If the binding affinity of the non-competitive inhibitor to free enzyme does not equal the binding affinity to the enzyme/substrate complex, the inhibition is considered what?
Mixed
If pure, alpha equals what?
alpha’
What is the Michaelis-Menton equation for non-competitive inhibition?
vo = to (vmax[S])/(alphaKm +alpha’[S])
With pure non-competitive inhibition, what happens to vmax, km, and the slope?
Vmax decreases, km remains the same, the slope changes
With mixed non-competitive inhibition, what happens to vmx, km, and the slope?
Vmax decreases, Km changes, the slope changes
What example of non-competitive inhibition was given in class?
Heavy metal poisoning
How do you find Ki and K’i for non-competitive inhibition?
1) LB plot (1/vo) vs 1/[S] at different [I]
2. plot the slopes of the LB plots vs [I] to find -Ki (x-intercept)
3) plot y-intercept vs [I} to find -K’i (x-intercept)
In which type of inhibition does vmax stay the same?
competitive
Does Vmax increase or decrease for uncompetitive and noncompetitive inhibition?
decrease
Does Km increase or decrease with competitive inhibition?
increase
Does Km increase or decrease with uncompetitive inhibition?
decrease
Does Km increase or decrease with non-competitive inhibition?
it can increase or decrease
In non-competitive inhibition, can the products formed by the inhibitor interact?
yes
