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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 Michaelis-Menten 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. Lineweaver-Burk plot
Invert the MM eqn: vo = Vmax[S]/(KM + [S]) (I.e. the MM Eqn = VVP 12-25) 1/vo = (KM/Vmax)(1/[S]) + 1/Vmax Then, this is the Lineweaver-Burk plot (VVP Eq. 12-29) 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 y-axis : 1/Vmax
● Intercept on the 1/[S] axis: -1/KM.
vo VVP Fig 12-3 Michaelis-Menten Graph VVP Fig 12-4 Lineweaver-Burk Plot Michaelis-Menten and Lineweaver-Burk Equations # 1
(No inhibitor present) Competitive Inhibition
Inhibitor and Substrate compete for the Active Site KI is the quantity
it captures the
inhibition power of
inhibitor I for the
enzyme E. Ki = [E][I] / [EI]
(VVP Eq. 12-30) Hence:
the inhibitor! Here:
= Competitive Inhibitor
EI = Enzyme-Inhibitor 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 12-7 Michaelis-Menten 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 12-8 Lineweaver-Burk Plot Intercept on x-axis: 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. Michaelis-Menten and Lineweaver-Burk Equations # 2
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- Fall '08