Exam 2 Lecture 13 Enzyme Kinetics Flashcards
A linear kinetic trend describes:
“Wishful thinking” as v = k[S]
A hyperbolic kinetic trend describes:
Michaelis-Menton Model
A sigmoidal kinetic trend describes:
Cooperative binding
Was is the equation for irreversible rxn and what does it allude to?
v = k[S]^n
Alludes to reaction rate as n indicates reaction order ie how many things have to come together to make product
1S—>P describes:
First order kinetics: v = k[S]^1
2S—>P or Sa + Sb —> P describes:
2nd order kinetics: v = k[S]^2 or k[Sa][Sb]
S—>P describes:
Zero order kinetics: v = k[S]^0 = k
Is a unimolecular rxn because an internal change. No breaking of bonds or do not an enzyme (uncatatalyzed) or enzyme is saturated ie all active sites are full
(Irreversible rxn)
S —>k1—>P; and the reverse from P to S (k-1)
REVERSIBLE rxn
Substrate is being both used and created
v = k1[S]^n - k-1[P]^m
At EQUILIBRIUM by definition, the forward rate equals
The reverse rate
v= k1[S] - k-1[P] = 0
k1[S] = k-1[P]
For a reversible rxn at equilibrium, we now can redefine our 2 equilibrium constants which are:
K(A) = association constant; making product k1/k-1
K(D) = dissociation constant; unmake product 1/K(A)
T/F: catalysis is not a 1st order rxn?
True
MM enzymes follow _ order kinetics
1st order kinetics
Km
Name and definition
Michaelis Constant
[S] where rxn rate is half maximal or half of the active sites are full
Related to the affinity of the enzyme for the substrate
Vmax
Name and definition
Maximum velocity
Maximum rate possible for a given concentration of enzyme
Kcat
Name and definition
Turnover number
How fast ES complex proceed to E + P
Number of substrate molecules converted per active site per time (first order rate constant sec-1)
Ks
Name and definition
N/A
A dissociation constant for substrate binding
Kcat/Km
Name and definition
Specificity constant
Measure of enzyme performance by predicting the fate of E*S (ability to convert substrate to product)
Laboratory condition:
[S] is much less than Km:
At very low substrate concentration :
Vo = (Vmax/Km)*[S]; that is, the reaction is first order with the rate directly proportional to the substrate concentration.
Laboratory condition:
[S] is much greater than Km:
At high substrate concentration, when [S] is much greater than Km, Vo = Vmax;
that is, the rate is maximal. The reaction is zero order, independent of substrate concentration.
Laboratory condition:
[S] = Km
When [S] = Km, then Vo = Vmax/2
Thus, Km is equal to the substrate concentration at which the reaction rate is half its maximal value.
What is the specificity constant?
(Kcat/Km)
A good enzyme would have:
Kcat much greater than k-1 and
Kcat/Km = k1
good enzyme will take enzyme substrate complex and go to product
A poor enzyme would have?
Kcat much less than k-1 and
Kcat/Km = 1/Km
bad enzyme we are falling apart and going back to substrate
Multiple binding site enzymes CAN follow Michaelis-Menten kinetics as long as they are __
NONCOOPERATIVE
- cooperative enzyme = sigmoidal shape bc active sites are not equivalent; they’re not independent
- If each active site is independent of its neighbor, we get hyperbolic curve we expect of MM enzyme (kinetics) noncooperative
Inhibitors can be either:
Irreversible (tightly bound to the enzyme) or reversible (rapid dissociation of the enzyme-inhibitor comples)
Reversible inhibitors use what type of interaction to bind?
Noncovalent interactions
Reversible inhibitors result in one of the following types of inhibition:
- Competitive
- Noncompetitive
- Uncompetitive
Which are allosteric inhibitors?
Noncompetitive and uncompetitive
Competitive inhibition:
Vmax is _
Km is _
Vmax is CONSTANT
Km is VARIABLE
no effect on Vmax but increase Km. Diminishes the rate of catalysis by reducing the proportion of enzyme molecules bound to substrate; takes longer to get to Vmax
Noncompetitive inhibition:
Vmax is _
Km is _
Vmax is VARIABLE
Km is CONSTANT
Km is unaltered and Vmax is decreased. Inhibitor and substrate can bind simultaneously to an enzyme at different binding sites; inhibitor lowers the conc of functional enzyme as it can bind to free enzyme or the enzyme-substrate complex
Uncompetitive inhibition:
Vmax is _
Km is _
Vmax is VARIABLE
Km is VARIABLE
Vmax and Km are reduced by equivalent amounts. Inhibitor binds only to the enzyme-substrate complex. The enzyme-substrate-inhibitor complex does not form any product
Irreversible inhibitors _ enzymes
Inactivate enzymes
Group-specific irreversible enzyme:
What it does:
Target a specific amino acid
Group-specific irreversible enzyme:
Specificity for active site:
Low
Group-specific irreversible enzyme:
Textbook example:
DIPF targets Serines
Substrate Analogs irreversible enzyme:
What it does?
Substrate mimic, modifies enzyme
Substrate Analogs irreversible enzyme:
Specificity for active site?
High
Substrate Analogs irreversible enzyme:
Textbook example?
TPCK looks like Phe to chymotrypsin
Suicide inhibitors irreversible inhibitor:
What it does?
Modified a substrate so is unable to form products
Suicide inhibitors irreversible inhibitor:
Specificity for active site?
Very high
Suicide inhibitors irreversible inhibitor:
Textbook example?
N,N-Dimethylpropargylamine inactivates FAD
Km that is low (small number)
Reaches Vmax at a lower [S]; tight binding
Km that is high (large number)
Reaches Vmax at a higher [S]; lower affinity ie higher [S] required to reach 1/2 Vmax
Km=
(k-1 +k2)/k1
