Question

1. Using the Michaelis-Menten equation, derive an expression that will determine Km as a function or in terms of Vmax, V0 and [S]. With this derived equation then calculate:

   a) Km

   B) Indicate at each substrate concnetration whether this Km changes with the changing S

   C) Using the double reciprocal plot, determine Km.

   
   

Answer 1

1.The rate of reaction when the enzyme is saturated with substrate is the maximum rate of reaction, Vmax.
The relationship between rate of reaction and concentration of substrate depends on the affinity of the enzyme for its substrate. This is usually expressed as the Km (Michaelis constant) of the enzyme, an inverse measure of affinity.

For practical purposes, Km is the concentration of substrate which permits the enzyme to achieve half Vmax. An enzyme with a high Km has a low affinity for its substrate, and requires a greater concentration of substrate to achieve Vmax.

2. The mechanism of enzyme catalyzed reactions is often studied by making kinetic
measurements on enzyme-substrate reaction systems. These studies include measuring rates
of the enzyme-catalyzed reactions at different substrate and enzyme concentrations. Here we
will look at a simple model for the catalytic behavior of an enzyme and the kinetic model that
arises from this model.
For many enzymes, if we were to plot the rate of catalysis, V (also known as the reaction
velocity), vs. the substrate concentration, [S] (at a fixed enzyme concentration) we would see a
plot as shown in figure 4.
Figure 4
Looking at this plot, we see that V varies linearly with [S] for small [S]. As [S] increases, V