Chapter 12: Enzymatic Kinetics Flashcards
Describe the michaelis menton steady state assumption
MM assumes that the rate of formation of the E-S complex equals its rate of breakdown
k1[E}{S}= K-1[ES] + K2[ES]
For a one-substrate enzymatic reaction, what’re the rate of formation and breakdown of ES equations?
V formation= k1[E}{S}
V breakdown= K-1[ES] + K2[ES]
What is the michaelis complex
the enzyme-substrate complex
What is the equilibrium assumption? when is this truly valid?
the assumption that E+S via K1/K-1 –>ES is only disturbed by ES via K2–>Product. this is only valid is the dissociation constant K2 of the ES complex (Michaelis complex) is «««_space;K1
What is the equation for the michaelis constant Km?
Km= (K-1 + K2)/ K1
What is Km?
the michaelis constant, the substrate concentration at which the reaction velocity is at half the max
What would happen if a reaction had a small Km?
it would achieve maximal catalytic efficiency at a low substrate amount.
What is Ks?
Ks is the dissociation constant of the michaelis ES complex (first step in enzymatic reaction) Ks=( [E]{S])/ {ES}
What would happen if Ks is high?
means that the enzyme has a low affinity for the substrate, will easily dissociate. Therefore, as the Ks decreases, the substrate affinity increases
What is Kcat?
the catalytic constant, the turnover number of an enzyme/ the number of reaction processes that each active site catalyzes per unit time (amount of times product is formed).
In what kind of system would Kcat=K2? what would the equation for Vmax be?
in a simple system. Vmax=kcat[enzyme total] or Vmax=K2[enzyme total]
When is Vmax is achieved
the maximal velocity of an enzyme. Occurs at increased substrate concentration when the enzyme is saturated and entirely in ES form.
As total enzyme concentration increases, Vmax ____
increases
If the substrate concentration is ««_space;than Km, ____ ES is formed, and E= Et
very little enzyme substrate complex is formed cause theres not a lot of substrate. Thus, the free enzyme concentration is essentially the total enzyme concentration.
What does it mean when Kcat/Km is high?
the enzyme has reached catalytic perfection. 1
General equation for Kcat?
Kcat= Vmax/[Et]
What kind of curve does a michaelis-menton enzyme present?
hyperbolic
In an MM enzyme reaction, Vo=Vmax when [S] is ____
when substrate concentration is HIGH. When [S] is low, which is the linear portion of the graph, there is essentially no ES and thus [E]=[Et].
If the concentration of substrate=Km, what does Vo equal?
When [S]=Km, Vo=1/2Vmax because Km is literalyl defined as the concentration of substrate in which the rate of teh reaction is at 1/2 the max.
In terms of Km and Ks, what is the equilibrium assumption?
Km=Ks (dissociation constant of ES back into the E+S form) when K2«<
The lower the Km, the _____ the fit between the enzyme and the substrate
the lower the Km, the better the fit between the enzyme and the substrate. An enzyme with a high Km has a low affinity for its substrate, and requires a greater concentration of substrate to achieve Vmax.
In a lineweaver burke plot, how do you determine Vmax and Km?
1/V0 intercept= 1/Vmax
1/S intercept= -1/Km