What information does the Km value determined for an enzyme and its substrate give us?
The reaction rate V is the number of reactions per second catalyzed per mole of the enzyme. The reaction rate increases with increasing substrate concentration [S], asymptotically approaching the maximum rate Vmax. There is therefore no clearly-defined substrate concentration at which the enzyme can be said to be saturated with substrate. A more appropriate measure to characterize an enzyme is the substrate concentration at which the reaction rate reaches half of its maximum value (Vmax/2). This concentration can be shown to be equal to the Michaelis constant (Km). Follow the link for diagram, and explanation. Don`t bother too much with the Maths! Basically the Km tells you how fast an enzyme can react. (probably oversimplifying here) Keep enzyme concentration constant and low, vary substrate concentration increasing it to obtain the plots shown in the diagram. Hopes that helps!
