Enzymes, being proteins, are very susceptible to temperature
It is important to remember what happens to proteins when they are
exposed to a high temperature.
Refer to the lesson, Basic biochemistry, paying
particular attention to Proteins.
Let's see how the temperature affects the working of an
- At low temperatures, the enzyme does not have enough energy to
function very efficiently.
- As the temperature increases, enzymes have more energy to work
better. At still higher temperatures some enzymes will begin to
denature - but there is now more energy to enable
enzymes to work even faster.
- At a certain temperature, the amount of enzymes working fast
(due to the increased energy) balances out the amount of enzymes
being denatured. We say that the enzymes are functioning
optimally at this temperature. The temperature is
therefore the optimum temperature for a particular
- At temperatures above this, the enzyme action will decrease as
the excessive heat will result in rapid denaturation.
The graph is not a simple bell-shaped curve. At lower
temperatures denaturation of enzymes is less severe but at
temperatures above the optimum, enzymes become denatured very
quickly and enzyme activity decreases very rapidly.
Denaturation is time dependent - if an enzyme
spends a long time at high temperatures, denaturation will be more
On the basis of temperature, enzymes have been divided into
- Thermophiles function optimally at
temperatures greater than 40°C, eg, thermophiles occur in
certain bacteria (Thermus aquaticus) that occur in hot
springs. These enzymes (Taq polymerase enzymes used in genetic
fingerprinting techniques) are stable at up to 95°C!
- mesophiles between 20°C and 40°C,
- psychrophiles function most effectively below
- Thermolabile enzymes function only at a
relatively low temperature.
Thermolabile enzymes are responsible for the coat colours on the
tips of the nose, ears and paws of Siamese cats.
These cats have darker colours at the tips of their bodies, where
the temperature is slightly cooler, and the enzymes will thus only
be active in these regions.
In the Arctic fox, in summer, the enzymes for
white coat colour are denatured, then as the weather gets colder,
the enzymes begin working and produce a white coat.
Can you also see what happens when people are
affected by fevers or extreme cold? At high or low temperatures,
enzyme activity is decreased or denatured, and many reactions
cannot be catalysed effectively.