Enzyme Kinetics Flashcards
What assumptions are made about substrate concentration when discussing Michaelis-Menten kinetics?
- The rapid equilibrium approximation: K1 and K-1 are small compared to Kp
- Initial rate/High [S]: [S] represents the free substrate concentration and is assumed to be close to the total substrate concentration because the reaction just began
- Initial Rate: The [ES] rapidly became steady because substrate is unlimited and [EP] is tiny
What is Vmax?
Vmax is the maximum velocity that would occur when all the enzyme is part of the enzyme-substrate complex
What is kp?
The reaction constant between the enzyme-substrate complex and the enzyme + product step
What is k-1?
Dissociation constant between the enzyme-substrate complex step and the enzyme + substrate step
What is the steady state assumption?
The concentrations of the intermediates of a reaction remain the same even when the concentrations of starting materials and products are changing
What does a high Kcat value signify?
Faster product production
What is the specificity constant?
Kcat/Km
Why is Kcat/Km the specificity constant?
The equation is basically the maximum product production per enzyme over the inverse efficiency of substrate binding.
What is a Lineweaver-Burk plot?
The plotting of Michaelis Menten kinetics as a double reciprocal
What can you tell by a Lineweaver-Burk plot?
- The slope is Km/Vmax
- y-intercept is 1/Vmax
- x-intercept is -1/Km
Why are inhibitors necessary in biological systems?
They regulate proteins
What is competitive inhibitor?
A type of reversible inhibition. The inhibitor competes with substrate for binding, then binds to the active site but does not affect catalysis.
What is a mixed inhibitor?
Inhibitor binds enzyme or enzyme-substrate complex. Binds to the regulatory site. Inhibits catalytic function and substrate binding.
What is the Michaelis constant? What does it represent?
Km represents a dynamic, in-progress reaction where the concentration of intermediate complexes does not change
How do you set up Michaelis-Menten conditions?
The concentration of substrate must be 100x larger than Ks and the fastest initial rate of product formation/substrate disappearance is measured
If given a graph with Velocity on the y-axis and [S] on the x-axis, how do you find Km?
Just like measuring the Kd, the Km is the x-coordinate at the 1/2 Vmax
What does Km approximate?
Km is a measure of roughly how much substrate is needed for full speed. The inverse substrate binding efficiency and the cellular [S]
What would happen is [S] was very different from Km?
The enzyme would be insensitive to changes
In regards to the Km value, what would indicate an inhibitor?
If the cellular levels of substrate is larger than the Km
In regards to the Km value, what would indicate an activator?
If the Km was larger than the cellular levels of substrate
Why are small Km values important?
The smaller the Km, the less E and S needed to make ES. Small Km values make the most efficient enzymes.
What is turnover?
The enzyme’s effect of turning substrate into product
What is the relation between turnover and Kcat?
They are the same. It’s the “limiting” rate of an enzyme catalyzed reaction
What is the Kcat equation?
Kcat=Vmax/[total E]
