Thousands of amino acids coil upon themselves to form a globular structure of
an
enzyme. The structure and interaction of the enzyme are very important for its
proper functioning.
Read types of enzyme inhibitors here
Factors affecting enzyme catalysis
In a living cell, many factors can influence the catalysis of an enzyme. The main factors affecting enzyme catalysis are:
- Temperature
- pH
- Substrate concentration
- Enzyme concentration
1. Effect of temperature on enzyme activity
The enzyme works to its maximum rate at a specific temperature, called optimum temperature. For example, the optimum temperature of enzymes present in the human body is 37 °C. An increase in temperature enhances or speeds up the rate of enzyme-catalyzed reactions, but only to a point.
As the temperature increases to a certain limit, heat energy contributes to the activation energy and also provides kinetic energy for the reaction and the reaction is speeds up (Figure 1). However, heat energy increases the vibrations of enzyme atoms when the temperature is elevated above the optimum temperature, and the globular enzyme structure is lost. This is called enzyme denaturation. Denaturation of enzyme reduces the conversion of substrate into products and thus affects the rate of an enzyme-catalyzed reaction.
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| Figure 1. Effect of temperature on enzyme catalysis. |
2. Effect of pH on enzyme activity
All enzymes work to their optimal rate at a small range of pH called
optimum pH. A minor change in this pH induces denaturation or complete
blockage of enzyme activity. Each enzyme has its optimum pH value unique to it
(Figure 2). For instance, pepsin, working in the stomach, is active at the
acidic pH (pH 2-3.5), while trypsin, working in the small intestine,
demonstrates its activity ate alkaline pH (pH 6-8). Amino acids present at the
active site are affected by the change in pH thus enzyme loses its ability to
catalyze substrate.
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| Figure 2. Effect of pH on enzyme catalysis. |
3. Effect of substrate concentration on enzyme activity
An increase in substrate concentration increases the rate of an enzyme-catalyzed reaction. If the concentration of enzymes is kept constant and substrate quantity is increased, a point is reached where the rate of reaction is no longer increased by any subsequent increase in the substrate.
The reason behind this is that all the enzymes are occupied in catalyzing the substrate and no free active site is present to accommodate incoming substrates. This state is called saturation of active site and thus the rate of reaction remains stable and does not increase (Figure 3).
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| Figure 3. Effect of substrate concentration on enzyme catalysis. |
4. Effect of enzyme concentration on enzyme activity
The concentration of the enzyme at a specific time in the presence of unlimited substrates is very important for the rate of reaction. An increase in the amount of enzyme by twofold can double the rate of reaction.
An increase in enzyme concentration means an increase in the number of active sites. So more active sites mean more conversion of substrate into products at a given time.
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