One of the characteristics of enzymes is that they are very sensitive to temperature. The following graph shows how the rate of an enzyme catalyzed reaction is affected by temperature.
The graph above tells you that as the temperature is increased, the rate of the enzyme activity increases. As you can see from the graph, the rate of reaction doubles as the temperature is increased by 10 degree Celsius. The rate is at its optimum at the optimum temperature of about 40 degree Celsius. If the temperature is increased further the rate will decrease. This is due to the effect of high temperature on the active sites of the enzymes. At a very high temperature, the shape of the active sites changed. When this happened, the substrate molecules will not be able to fit in into the active site. As a result, the reaction stops. At this stage, the enzymes are said to be denatured and this is irreversible. Unlike at a very low temperature, though the enzymes are not active, they still can be activated if the temperature is increased.
