Enzyme Kinetics Flashcards
In the Michaelis-Menten Kinetcs, the ___ is always rate limiting step
k2/kcat
Enzyme kinetics are important for:
- Drug design
- Drug interactions
- Toxins (making anti-toxins)
In enzyme kinetcs catalyzed reactions, the stubstrate:
will be used up until equilibrium is attained
In the very beginning there is a very ____relationship
linear
As substrate comes ____, product goes ____
down; up
What is going on during pre-steady state
concentration of ES is building up
What is going on during the steady state
After pre steady state, concentration of ES and any other intermediates reaches point where concentrations are approx constant,
What is the steady state kinetics experiment like
- Set up several reactions
- [E] same in each
- Different substrate conc.
- Plot amount of P formed against time
- Measure velocity
What does the michaelis menten equation describe
the curve obtained by plotting Vo, initial velocity against [S], the substrate concentration
What is Km
The michaelis menten constant which is the substrate concentration at which Vo= 1/2 Vmax
When substrate concentration is much less than Vmax, what kind of relationship do you get
linear= 1st order kinetics
When substrate concentration is much higher than Km:
The eqn reduces to Vo=Vmax; adding more substrate doesnt make a difference. This is called 0 order kinetics.
What is the lineweaver-burk equation
Transforms michaelis menten equation into equation that gives a straight line plot
What is the slope = to in a lineweaver burk plot
Km/Vmax
What does Km depend on
- Substrate used
- pH
- Temperature
Hexokinase is the first enzyme in
glycolysis; phosphoralates glucose
What does Km mean
Can be used to calculate the fraction of active sites filled at any substrate concentration
Km is related to the rate constants of each step in the ____reaction
catalytic
WHat is Kd
the dissociation constant for the ES complex; provides a measure of the affinity of the enzyme for its substrate.
Another way to describe kcat is that it is the:
turnover constant=number of substrate molecules converted to product per unit time by a single enzyme molecule saturated with substrate.
What is catalytic efficiency = to
the factor kcat/km
What are two broad classes of enzyme inhibitors
- Reversible
2. Irreversible
Aspirin inhibits which enzyme
cylooxygenase; which is used for inflammation/pain
ACE inhibits which enzyme
angiotensin converting enzyme; which then dec blood pressure
Statins inhibit which enzyme
HMGCoA reductase; lowers cholestrol
Simbrinza inhibis which enzyme
Carbonic anhydrase; glaucoma
What are the three types of reversible inhibitors
- competitive
- uncompetitive
- mixed inhibition (non-competitive)
What is a competitive inhibitor
a compound that resembles a normal substrate; competes with substrate for binding to active site but no reaction occurs when bound.
What does a compettive inhibitor curve look like
Vmax doesnt change, just takes more substrate to get there. Km (increases) and slope changes.
What is DIFP
An irreversible inhibitor; it combines with reactive serine 195 and makes a covalent bond and just sits there. Doesnt come off
What are target enzymes for DIFP
- Acetylcholinesterase
2. Chymotrypsin
What is penicillin
An irreversible inhibitor; once bound in active site, beta lactam ring covalently reacts with active site serine (enzyme activity irreversibly destroyed)
What are suicide inhibitors
Special class of irreversible inhibitor. Bind to active site and begin to participate in normal enzyme reactions. Form an intermediate that is covalently bound to an active site reactive group as a normal step in reaction. Do not undergo further steps
What is an ex of a suicide inhibitor
Flourouracil: impt chemotherapeutic agent in cancer treatment that targets production of DNA precursors.
What are the four major mechanisms of regulation of enzyme activity
- Stimulation and inhibition by control proteins.
- Reversible covalent modification
- Proteolytic activation
- Allosterism
Neutrophils are
the first cells that arrive and invade foreigners. Break down ECM in area.
What is alpha 1 antitrypsin
potent elastase inhibitor; binds strongly, blocks active site – deficiency causes emphysema (CT in lung damaged)
What is elastase
released by neutrophils responding to bacterial infection; degrades collagen and elastin
What is reversible covalent modification
reversible attachment of small functional group. Often phosphoryl group. Alters activiy: enzymes in glycogen metabolism
WHat is proteolytic activation
Zymogen: inactive precursor of enzyme; irreversibly activated by proteolytic cleavage of one or more peptide bonds.
What are examples of proteolytic activation
blood clotting enzymes, digestive enzymes, angiotensin II
Kinases
phosphoralates things
What is allosterism
A change in the conformation and as a result activity - of an enzyme resulting from the binding of a compound at a site on the enzyme other than the active binding site.
What is a modulator (effector)
regulatory metabolite that modulates enzyme activity, usually by reversible, non covalent binding
Allosteric enzymes show ____rate curves
sigmoid (instead of hyperbolic)
Positive modulators ____substrate affinity
increase
Negative modulators (inhibitors)____substrate affinity
decrease
Sigmoidal substrate activity curves are consistent with subunits exhibiting
cooperativity (hemoglobin)
WHat is cooperativity
The influence of the binding of a ligand to one subunit on the binding of a ligand to a second subunit; usually involves conformational change
What are the two observations that the models for allosterism explain?
- Sigmoidal curve with substrate alone (no modulators)
2. Change in curve in response to positive and negative modulators
What are the two models of allosterism
- Concerted (symmetry) model
2. Sequential model
What does the concerted/symmetry model propose
an allosteric enzyme molecule can exist in only two states:
- Tense state
- Relaxed state
What is relaxed state
All subunits are in active or high affinity state
What is tense state
all subunits are in inactive or low affinity state
What is an activator:
Binds to R form, shifting equilibrium and increasing substrate binding
What is an inhibitor
Binds preferentially to T form, shifting equiliubrium, decerases substate binding
What is the sequential model
Binding of ligand to any one subunit causes a conformational change in that subunit; change partially transmitted to one or more adjacent subunits.
What is activator binding
causes conformational change to increase subunit affinity for substrate or can increase effect transmitted by subunit
What is inhibitor binding
Causes conformational change to decrease subunit affinity for substrate or can dec effect transmitted by subunit.
The best example of allosteric regulation is:
hemoglobin
