Wednesday, 25 January 2017

Km + [S] Michaelis-Menten equation


Different enzymes reach Vmax at different [S] because enzymes differ in their affinity for
the substrate or Km.
1) The greater the tendency for an enzyme and substrate to form an ES, the
higher the enzyme’s affinity for the substrate ---> lower Km.
2) At a given [S], the more enzyme will be in ES for an enzyme with a higher
affinity
i.e. the greater the affinity, the lower the [S] needed to saturate the
enzyme or to reach Vmax.
Enzyme-substrate affinity and reaction kinetics are closely associated
[S] at which vo=1/2Vmax = Km
Km is a measure of enzyme affinity
Km = k-1
k1 reflection of association and dissociation of
ES
a small Km (high affinity) favors E + S ----> ES
a large Km (low affinity) favors ES -----> E + S
meaning that the lower the Km, the less substrate is needed to saturate the
enzyme.
We would like numbers of Vmax and Km for a means of comparison among enzymes.
It is difficult to estimate Vmax and Km from a typical graph of [substrate] vs. velocity.
These two parameters are used to describe the efficiency of enzymes; must be an easier
method for measuring these parameters.
Done by transformation of the date by taking the reciprocal of both sides of the equation -
--> double reciprocal plot or Lineweaver-Burke plot.
Vo = Vmax[S]
Km + [S]
1 Km 1 1
Vo = Vmax [S] + Vmax y=mx+b

1 comment:

  1. Selective, high affinity α4β1 (Very Late Antigen 4; VLA-4) inhibitor; Displays 200-fold selectivity for the activated form of α4β1 (KD = 70 pM; IC50 = 0.004 μM). BIO 1211

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