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Lec 11
We talked about basics of
Michaelis Menten
dependence of enzymatically catalized reaction on
substrate concentration is hyperbolic,
with two parameters
: 1) Vmax maximum velocity, with
particular enzyme concentration 2) substrate concentration when ½ of Vmax which is Km.
Km is
substrate concentration, it is NOT velocity, it is substrate concentration where ½ Vmax. Hyperbola
approaching Vmax, ½ Vmax substrate concentration equals Km. One can relate Km to the kinetic K. The
equilibrium constant for binding of substrate to form reversible complex will be k1/k1. Km is the sum of
2 dissociation rate constants (dissociation back to free enzyme and substrate and dissociation constant to
the product divided by the association constant). Km is independent of the delta G between substrate and
product, but is related to the Activation energy change
, Km is sometimes approximation of equilibrium
between substrate and transition state.
Free energy of activation is expressed with Kp, one can estimate
uncatalyzed rate of reaction
. And drop of activation energy, increase of rate constant is measure of
how good catalyzed is.
The lineweaver Burk transformation: x intercept is 1/Km (inverse of substrate concentration), y intercept
is 1/Vmax.
The slope of this line Km/Vmax.
When
increasing Vmax
, (is measure of Vmax=Kcat times
the total enzyme concentration)
puts the value of 1/Vmax lower and lower
.
Km is the tendency of
substrate enzyme to dissociate back to free
, the
lower Km
(look at absolute terms) the
higher the
affinity
of the enzyme for the substrate,
and higher the value of x intercept.
Not all enzymes deal with transformation of single substrate to single product. Diagram, implicit
mechanism, reaction starts with binding of A, and when A is bound, B can bind as well
obligate
binding order.
Also there is possible of AB and BA binding which is random binding order. When
random order
, there are
two separated sites for 2 substrates and sites do not talk to each other
, substrate
just bind with their own affinities
, the binding does not affect affinity of the other one

non
cooperative binding.
When handling the two molecules of the same substrate,
and substrate binding
sites do not talk to each other, to find Km, you will get the plots and one sees apparent Km is unaffected
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 Fall '08
 Hoffmann,J

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