Enzyme Kinetics

 

Enzyme Kinetics

In an enzyme reaction S → P, the rate of the reaction is depend on the substrate concentration. At low substrate concentration the rate of reaction ‘v’ is proportional to substrate concentration. As the substrate concentration is increased, the velocity of reaction falls and is no longer proportional to the substrate concentration. With the further increase in substrate concentration, the rate of reaction becomes substrate and independent of substrate concentration. The enzyme at this stage shows the Saturation effect, i.e. it has become saturated with the substrate and levels off to a flat plateau at high substrate concentration.

            The plateau occurs because the enzyme is substrate, meaning all available enzyme molecules are tied up with substrates. Any additional substrate molecule will have to wait around till another enzyme is available, so we can say rate of reaction is limited by enzyme concentration. This maximum rate of reaction is characteristic of a particular enzyme at a particular concentration and is known as the maximum velocity or V_max.

                The substrate concentration that gives a rate that is halfway to V_ma is called K_m and is useful measure of how quickly reaction rate increases with substrate concentration. K_m is also a measure of an enzyme affinity to its substrate, while a higher K_m correspond to a lower affinity for the substrate.

            These saturation effect led Michaelis and Menten to general theory of enzyme action and kinetics in the year 1913.

Michaelis-Menten plot

                                         V_max.(S)

                                 V=    -------------

                                           K_m+(S)

Effect of change in concentration of substrate on enzyme activity

                           

                            S      = Substrate

                            V     = Reaction velocity

                            V_max = Maximum velocity

                             K_m   = Michaelis-Menten constant