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Unformatted text preview: nten equation,
The basic equation of enzyme kinetics. Two important consequences from the MM equation:
(i) KM is the substrate concentration at which the reaction velocity is half maximal.
(ii) When [S]<<KM: vo = Vmax[S]/KM Summary of special positions on the MichaelisMenten graph
vo = Vmax[S]/(Km + [S]) (The “MM Equation”) KM and Vmax are the
quantities of interest
which capture the
character of the
catalysis of substrate S
by enzyme E Lehninger f06.12, 4th ed. LineweaverBurk plot
Start from:
Invert the MM eqn: vo = Vmax[S]/(KM + [S]) (I.e. the MM Eqn = VVP 1225) 1/vo = (KM/Vmax)(1/[S]) + 1/Vmax Then, this is the LineweaverBurk plot (VVP Eq. 1229) with
● 1/[S] as the independent variable, and
● 1/vo as the dependent variable.
This equation describes a straight line with:
● Slope: (KM/Vmax)
● Intercept on the yaxis : 1/Vmax
● Intercept on the 1/[S] axis: 1/KM.
vo VVP Fig 123 MichaelisMenten Graph VVP Fig 124 LineweaverBurk Plot MichaelisMenten and LineweaverBurk Equations # 1
(No inhibitor present) Competitive Inhibition
Inhibitor and Substrate compete for the Active Site KI is the quantity
of interest:
it captures the
inhibition power of
inhibitor I for the
particular reaction
catalyzed by
enzyme E. Ki = [E][I] / [EI]
(VVP Eq. 1230) Hence:
the SMALLER
the Ki,
the BETTER
the inhibitor! Here:
I
= Competitive Inhibitor
EI = EnzymeInhibitor Complex
S = Substrate
E = Enzyme
P = Product
ES = Michaelis complex Competitive Inhibition
MM equation: vo = Vmax[S]/(αKM + [S])
Where: α = 1 + [I]/KI and KI = ([E][I])/[EI]
LB equation: 1/v0 = (αKM /Vmax) (1/ [S]) + 1/ Vmax
VVP4e Fig 127 MichaelisMenten Graph Measure data for increasing values of [I]
You don’t know α yet….
You get α from the intercept in the LB plot
on the right VVP4e Fig 128 LineweaverBurk Plot Intercept on xaxis: 1/[S] = 1/(αKM)
Since KM is known, α can be calculated.
Then with the definition of α and the known [I],
KI can be calculated. MichaelisMenten and LineweaverBurk Equations # 2
Competitive Inhib...
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 Fall '08
 HOL
 Biochemistry

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