C.7.2

=Determine Vmax and the value of the Km by graphical means=

At high concentrations, the **rate of a reaction of the enzyme (or enzyme activity) reaches a maximum value called V max**. At Vmax the enzyme is saturated, all the active sites are used up, the enzyme cannot work any faster, it is working at its greatest rate. The curve of the graph will be horizontal and there will be no further change in the rate as the concentration of the substrate increases. To find V max, plot a graph of the rate of the reaction /enzyme activity (y-axis) against the concentration of substrate(s) (x-axis). The graph is a curve and will flatten out at V max.

http://dbs.umt.edu/courses/fall2006/bioc380/lectures/013/images/mm-curve.jpg
 * Km** is defined as the **substrate concentration at 1/2 Vmax**. The rate of the reaction is at half its maximum rate. In terms of the relationship between Km and the enzyme activity is that as the Km increases the activity of the enzyme decreases. Km is called the Michaelis-Menten constant. Since Km is 1/2 V max, Km is the mid point between 0 and V max.