L6: Enzymes Flashcards
competitive inhibitor
- binds to substrate binding site
- competes with substrate
- binds only to the free enzyme not ES complex
- affinity of substrate decreased when inhibitor is present
- Km is increased because it takes more substrate to compete out the inhibitor
- Vmax unchanged
noncompetitive inhibitor
- binds to allosteric site
- does not compete with substrate for binding to the enzyme
- binds to either enzyme or enzymes substrate complex
- Vmax decreases
- Km stays the same -substrate can still bind in same manner
- F-1,6-Bpase inhibition by AMP
uncompetitive inhibitor
- binds to enzyme only after substrate has bound
- binds only to ES complex
- Km and Vmax decreased
- AchE inhibitors for Alzheimer’s
irreversible inhibitor
- covalently modifies and permanently inactivates the enzymes
- Vmax decreases
- No effect on Km
- penicillin example
general characteristics of enzymes
- protein catalysts
- increase rate of reaction
- recognize specific substrates and catalyze specific types of reactions
enzymes and equilibrium constant
- increase rate of reaction but DO NOT CHANGE THE EQUILIBRIUM CONSTANT
Keq > 1
- equilibrium favors products
Keq < 1
- equilibrium favors reactants
kcat
- the turnover number
- number of substrate molecules converted to product per second by a single enzyme active site
Vmax equals
- kcat[E]
enzymes and activation energy
- lower the activation energy of a reaction by stabilizing the transition state
transition state
- the structure of a molecule as it converts from substrate to product in the enzyme-substrate complex
Vmax
- the maximum velocity of an enzyme
Km
- the substrate concentration that gives 1/2 the Vmax
- Michaelis-menten constant
Michaelis mentin equation
v = (Vmax[S]) / (Km+S)
Michaelis mentin plot
- plots substrate concentration versus velocity
Lineweaver Burke plot
- inverse plot
- plots 1/substrate versus 1/velocity
slope of line weaver burke plot
- slope = Km/Vmax
isozymes
- normal gene underwent gene duplication to form two identical genes
- these genes underwent mutation and selection to form two or more similar genes for slightly altered enzymes
do all duplicated genes produce functional proteins?
- no
are all isozymes useful/significant?
- no
allosteric enzymes
- have multiple active sites that are cooperative
- more sensitive to [S] than other enzymes
- give sigmoidal curve
- bind effectors at an allosteric site that is different from active site
- binding at one site changes the conformation of the enzyme, which affects affinity at the active site
positive regulator
- alters the active site to allow substrate to bind more effectively
- binding of oxygen to hemoglobin
negative regulator
- alters the active site to prevent binding of substrate, which decreases reaction rate
- PFK inhibition by ATP
when the end product level is high?
- end product acts as a negative regulator and binds to allosteric site
- substrate cannot bind to active site, and subsequent reaction stops
Lineweaver burke competitive inhibitor
- -1/Km moves to the right because it gets bigger
- 1/Vmax does not change
- looks like a bow tie
lineweaver burke noncompetitive inhibitor
- -1/Km does not change
- 1/Vmax goes further up because you are decreasing Vmax
- looks like a fan
line weaver burke uncompetitive
- -1/Km goes further to the left
- 1/Vmax goes further up
- Parallel lines
Ki
- affinity for an inhibitor
Poor inhibitors
- Ki > 10 uM
normal inhibitors
- Ki = 10 uM - 100 nM
excellent inhibitors
- Ki < 1 nm (tight binding)
