Enzyme Kinematics Flashcards
Types of enzymes and inhibition, Vmax and Km, etc.
Substrate
What enzymes interact with
Enzyme binding site
Where intermolecular interactions occur
Enzyme catalytic site
Where the reaction is catalyzed
Induced fit model
Enzyme and substrate shape affect each other; explains stabilization of the transition state
Ligand
Regulatory molecules and substrates (any substance an enzyme interacts with)
Orthosteric regulation
Elements that interact with an enzyme at its active site
Allosteric regulation
Elements that bind to an enzyme at sites other than the active site
Oxidoreductases
Catalyze redox reactions
Transferases
Transfer functional groups between molecules
Hydrolases
Catalyze hydrolysis
Isomerases
Catalyze isomerization; name often includes “mutase” suffix
Lyases
Cleave bonds using mechanisms other than hydrolysis
Ligases
Join molecules together with covalent bonds
Alcohol dehydrogenase
Type of oxidoreductase; converts alcohols to aldehydes
Phosphatase
Remove phosphate groups
Kinases
Type of transferase; add phosphate groups to acceptor molecules
What type of bonds do enzymes use to bind to substrates?
Noncovalent
Feedback
Downstream product of a pathway reaches backward to regulate upstream steps
Feed-forward regulation
Product helps a later step that it is not directly involved in
Cooperativity
An enzyme binding one ligand makes it easier to bind the second; each subsequent ligand is easier to bind (ex: hemoglobin)
Sigmoidal curve (S shape)
Curve indicating cooperativity
Hill Coefficient
Indicator of cooperativity
>1 = positive cooperativity
0 = no cooperativity
<1 = negative cooperativity
Phosphorylation
Covalently adding a phosphate group to a protein
Zymogen
Inactive enzyme precursors
Cofactors
Molecules required by enzymes to function
-Can be organic or inorganic
Coenzymes
Organic cofactor molecules (vitamins)
Prosthetic groups
Coenzymes that are tightly or covalently bonded to their enzymes (ex: heme)
Holoenzyme
Enzyme + all cofactors and coenzymes
Apoenzyme
Only enzyme, without addition of cofactors
Michaelis-Menten Model
Explains how the rate of an enzyme catalyzed reaction is dependent on the concentration of the enzyme and its substrate
Saturation
All enzyme molecules are occupied; reaction is at max velocity
Km
Substrate concentration that corresponds to 1/2 of Vmax; measure of affinity (higher = greater affinity)
Reaction velocity equation
(Vmax*[S]) / (Km + [S])
Michaelis-Menten Plot
Reaction rate as a function of substrate concentration
Lineweaver-Burk Plot
Double reciprocal transformation of Michaelis-Menten Plot
x-intercept value of Lineweaver-Burk Plot
-1/Km (higher Km = closer to origin)
y-intercept value of Lineweaver-Burk Plot
1/Vmax (higher Vmax = closer to origin)
Competitive inhibitor
Compete with the substrate for the active site
-Vmax stays the same
-Km increases
-Steeper LBP slope
Noncompetitive inhibitor
Interact with the enzyme and enzyme-substrate complex allosterically (bind to both with equal affinity)
-Vmax decreases
-Km stays the same
-Steeper LBP slope
Uncompetitive inhibition
Interact allosterically with the enzyme-substrate complex to prevent enzyme from converting substrate to product after substrate has already bound
-Vmax decreases
-Km decreases
-x and y intercepts on LBP move away from origin
Mixed inhibition
Can bind to allosteric site on free enzyme or to enzyme-substrate complex
-Vmax decreases
-Varying effects on Km:
-Binds free enzyme: Km increases
-Binds E-S complex: Km decreases
