2 - Basic Enzyme Kinetics - Rate Flashcards
Ks
Analysing enzymes as catalysts
- catalysts only affect rates (not equilibria)
- enzymes catalyse by stabilising ‘transition states) and thus lowering ‘activation barriers’
- enzymes bind their substrates to form ESC
- contact between enzymes and substrate (E) and (S) occur at active sites involving specific chemical groups on the enzyme
- Details of these reactions can be determined by studies of ‘enzyme kinetics’ = rates of enzyme-catalysed reactions
Summary of basic steady-state enzyme kinetics
Michaelis enzyme model
- E and S react to give ES complex
- this can be shown as an equilibrium:
- E + S <-> ES
- ES complex reacts to release product P and to regenerate the free enzyme:
- ES <-> E + P
So:
- E+S <-> ES -> E + P
Michaelis-menten enzyme equation
V = Vmax x (S)/(Km + (S))
V =
Vmax = max rate of enzyme catalysed reaction
S = Substrate quantity
Km = Michealis constant -
How to derive Michaelis-menten enzyme equation
How to derive the Km (michealis constant)
- why is important
The numerical value of half of Vmax
- with Km can then derive substrate concentration in michealis- menten enzyme equation
Proof half Vmax = Km (michealis constant)
What is Kcat
Enzyme turnover number
Units for enzyme efficiency
Kcat/Km s-1 M-1
Affinity of different enzymes to different substrates
- Different substrates have different affinities if they bind to the active site of the same enzyme
- means that Km is different
- So v is different in michealis-menten equation
The Lineweaver-Burk plot info
What is Km (michealis constant)
- what does it show
- a measure of affinity
- shows the substrate range over which the enzyme works
What is Vmax
Shows how fast the enzyme can work
How to determine Vmax and Km
- need to determine v at a series of values of (S)
- can use the Lineweaver-Burk plot for a series of experimental data of (1/v) or (1/S) to work out the values
