A high fever can cause a denaturation, or change in shape, of an enzyme, resulting in less activity for the enzyme to catalyze reactions in the body, according to the BBC. When there is elevated temperature in the body, the enzymes cannot carry out normal functions. The enzyme's activity gradually increases with a rise in temperature up to the limit of body temperature, and then diminishes at higher temperatures.
Worthington Biochemical Corporation states that most enzyme activity will be reduced at higher temperatures. Most animal enzymes become denatured above 40 degrees centigrade. Class notes from the School of Engineering at Rensselaer Polytechnic Institute point out that high temperatures affect enzymes in two ways. One is the denaturation of the enzyme. The other is the direct influence on the reaction rate constant. The Arrhenius equation can be used to estimate enzyme reactivity to temperature. The range of temperature, where an enzyme shows activity, falls between the melting point, which is zero degrees centigrade, and boiling point of water, which is 100 degrees centigrade.
If the temperature is too low, the reaction rate will not be noticeable, notes Rensselaer Polytechnic Institute. When the temperature is above 100 degrees centigrade, thermal deactivation occurs. This deactivation limits enzymes' function in their environment. In humans, deactivation can occur at temperatures as low as 45 to 55 degrees centigrade. Depending on the enzyme process, the result may be irreversible or reversible.