Enzyme Inhibition Flashcards
What are the 3 types of enzyme inhibition?
Competitive
Non-competitive
Un-competitive
What are the characteristics of competitive inhibition?
Vmax is not affected-Inhibition can be overcome by increasing substrate concentration
Km (Km apparent) is increased
Km app= Km (1+[I]/Ki)
What are the characteristics of non-competitive inhibition?
Km is unchanged
Inhibitor does not compete with substrate
Inhibitor binds to either the enzyme or the enzyme-substrate complex
Vmax is reduced
Vapp= Vmax* (1+[I]/Ki)
What are the characteristics of un-competitive inhibition ?
The inhibitor binds only to enzyme-substrate complex
Vmax and Km are both decreased
Vapp=Vmax * (1+[I]/Ki)
Kapp=Kmax * (1=[I]/Ki)
What is cooperativity ?
Binding of one substrate facilitates the binding of subsequent substrate molecules
More than one binding site and more than one subunit
What is Hill Equation?
V=(Vm[S]^n)/(K^ 0.5 +[S]^n) K^ 0.5= [S] at half Vmax N= Hill number Measure of cooperativity The large the n the more cooperativity If n=1--> Michaelis-Menten equation If n>1---> positive If n<1---> negative
What is a positive cooperativity ?
A greater change in activity over a narrower range of [S]
Enzyme without S boiuund is in tense T state
Binding of S promotes change to relaxed R state
Inhibitors and activators stabilize tense and relaxed states
What are the types of allosteric effectors?
Homotropic-substrate may also be an effector
Heterotropic-a substance other than the substrate
Positive effectors-activators
Negative effectors-Inhibitors
So we can have a combination of homotropic activators or heterotropic inhibitors or vice versa
Homotropic effectors are almost always positive and usually at higher concentration
What are other types of effectors?
V-system effectors- affect Vmax by do not affect K^0.5
K-system effectors-affect k^0.5 but do not affect Vmax
