Enzyme Kinetics Flashcards
What is Vmax?
The maximum rate of a catalysed reaction
What is KM?
The concentration of substrate that causes the rate of a catalysed reaction to be 50% of the maximum
What is V?
The rate of a catalysed reaction
What does a graph of concentration of substrate against rate of reaction look like?
Steep gradient, decreasing in gradient until tapers off at Vmax
What is ES?
The Enzyme Substrate intermediate/complex
How stable is the enzyme substrate complex?
Inherently unstable
What is the enzyme substrate complex?
The point at which potential energy is highest and the reaction could go forwards or backwards
What makes the enzyme substrate complex inherently unstable?
The activation energy barrier
What is the symbol for the Michaelis constant?
KM
What is the equation for the Michaelis constant?
KM = (k-1 + k-2)/k1
What do k1, k-1 and k-2 stand for in the Michaelis constant equation?
k1 - forward rate constant for enzyme association with substrate
k-1 - backward rate constant for enzyme association with substrate
k-2 - forward rate constant for enzyme conversion of substrate to product
How is Vmax measured?
V0 (initial reaction velocity) is measured at a known substrate concentration.
This is repeated at increasing substrate concentrations
The results are plotted as a function of substrate concentration
As substrate concentration increases, V0 approaches Vmax
What has to be true for there to be a Vmax?
Enzyme concentration must be constant
Why is trying to determine Vmax and KM experimentally not straightforward?
The kinetics are not linear so the reaction velocity never truly reaches Vmax
What is the Michaelis-Menten equation?
V = (Vmax . [S])/(KM + [S])
What is the inverse of the Michaelis-Menten equation?
1/V = KM/Vmax . 1/[S] + 1/Vmax
How would you do a Lineweaver-Burk plot?
Take the inverse of the Michaelis-Menten equation, which is equivalent to y=mx+c and plot the line accordingly
What are the y-intercept and x-intercept on a Lineweaver-Burk plot?
y-intercept = 1/Vmax aka. Vmax x-intercept = -1/KM aka. KM
What are the x- and y-axes on a Lineweaver-Burk plot?
x-axis = 1/[S] y-axis = 1/V0
What is the gradient on a Lineweaver-Burk plot?
KM/Vmax
What substrate concentration will an enzyme with a low KM need to reach Vmax?
Low
What substrate concentration will an enzyme with a high KM need to reach Vmax?
High
Can enzymes have the same Vmax but different KM?
Yes
Is competitive inhibition reversible?
Yes
