Enzyme kinetics Flashcards
What is the Vmax?
The maximum rate of a reaction for an enzyme as it is fully saturated by substrate.
What is Km?
50% of the Vmax
What is Km equivalent to ?
The substrate concentration in moles.
What does the Michaelis-Menten kinetic model do?
Create relationship between the concentration for the substrate and the rate of the catalysed reaction.
What type of graph does the Michaelis-Menten kinetic model create?
Hyperbola curved graph.
How do you measure Vmax and Km?
- Measure initial reaction velocity ,V0, at known substrate concentration and repeat at increasing substrate concentrations
- Then transform the Michaelis-Menten into a straight line equation and plot
- this new graph is then called a Lineweaver-burk plot
What does a high Km value mean?
Enzyme only needs a small amount of substrate to work at half-maximal velocity
What does a low Km value mean?
Enzyme needs a large amount of substrate to work at half-maximal velocity
What are the 4 types of enzyme inhibition?
Reversible competitive, reversible non-competitive, irreversible non-competitive and feedback inhibition.
Describe Reversible competitive inhibition.
binds to active site and blocks substrate access (orthosteric inhibition- same site), doesn’t change the Vmax but Km varies
Describe reversible non-competitive inhibition.
binds to allosteric site and changes the enzyme’s conformation (allosteric inhibition- diff. site), Km stays same but Vmax varies
Describe irreversible non-competitive inhibition
involves formation or breakage of covalent bonds in the enzyme complex
What can control allosteric enzyme activity?
allosteric inhibitors and allosteric activators.
Describe feedback inhibition.
- Final product can inhibit an earlier reaction in the pathway
- form of allosteric control
- These allosteric enzymes that do this do not follow the Michaelis-Menten kinetic model
- Forms a sigmoidal curved graph
What is K1?
The forward rate constant for enzyme association with substrate.
What is K-1?
The backwards rate constant for enzyme dissociation from the substrate.
What is K2?
The forward rate constant of enzyme conversion of substrate to product.
Why can’t Vmax and Km be accurately measured from a hyperbolic V/[S] graph?
The kinetics are not linear and the velocity never truly reaches Vmax.
