Lecture 1 - Enzyme Kinetics Flashcards
What is the steady state assumption in the Michaelis-Menten equation?
The rate of ES production is equal to the overall rate of all the reactions that decrease [ES].
What is the Km?
The substrate concentration at which the reaction rate is half the maximal rate (Vmax).
What does it mean if an enzyme has a low Km?
It achieves maximal catalytic efficiency at low [S]
What is Kcat?
The turnover number- the number of reaction processes that each active site catalyses per unit time.
What are the disadvantages of the Lineweaver-Burk plot?
Most measurements of [S] are at high values, and the 1/[S] values end up crowded on the left side of the graph- makes drawing the straight line difficult and inaccurate.
For small [S], there can be large errors in Km and Vmax.
What are the disadvantages of the Hofstee-Eadie plot?
Can have large errors- both coordinates contain the dependent variable.
What are the advantages of the Hanes-Woolf plot?
There is equal weighting of the data, so a better fit of the straight line.
Describe a competitive inhibitor.
- resembles substrate structure
- competes directly with substrate for active site
- binds to the active site but is unreactive
What parameters are affected by competitive inhibition?
Km - affecting the affinity for substrate.Vmax is not affected by competitive inhibition.
Describe an uncompetitive inhibitor.
- binds to an allosteric site on the ES complex
- can cause distortion of the active site
What parameters are affected by uncompetitive inhibition?
Both Vmax and Km
Describe a mixed inhibitor.
- bind to an allosteric site
- can bind to free enzyme or ES complex
- effective inhibition at both low and high substrate concentrations
Which parameters are affected by mixed inhibition?
Both Vmax and Km.
Describe a non-competitive inhibitor.
- binds at an allosteric site
- effectiveness depends on inhibitor concentration
Which parameters are affected by non-competitive inhibition?
Vmax lowers as inhibitor concentration increases.Km is not affected as EI can still bind substrate.
How can competitive inhibition be overcome?
The inhibitor is displaced at high concentrations of substrate.
How can uncompetitive inhibition be overcome?
Lowering the concentration of the substrate makes the effect of the inhibitor negligible.
What are the features of a perfectly evolved enzyme?
Diffusion controlled. Km is much higher than physiological [S] value.
