What is Enzyme Activation Energy


Enzymes are proteins that act as catalysts. Enzymes accelerate the speed of chemical reactions and regulate metabolic processes.
As catalysts, they reduce the activation energy of chemical reactions and are not used up themselves.

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Enzymes as biocatalysts simply explained - what are enzymes? Enzyme Activity - Metabolic Biology

How enzymes work

So that enzymes can perform their function, the substance to be converted (substrate) is bound to a specific point on the enzyme, the so-called active center, via intermolecular interactions. An enzyme-substrate complex is created. The substrate is then converted and the reaction product is then released from the enzyme again. This makes the enzyme available for new substrate conversions.

Enzyme lock and key principle

However, enzymes cannot convert any substrate. The tertiary structure plays a major role in this. Due to the tertiary structure, the enzyme has an indentation into which the substrate fits. The enzyme and substrate work according to the lock and key principle. If the substrate does not fit into the indentation of the enzyme, it cannot be bound and converted in it either.

Substrate specificity of enzymes

So enzymes can only convert certain substrates. This property is called substrate specificity. A distinction is made between group specificity and absolute specificity. Enzymes with an absolute specificity can only convert a certain substrate, enzymes with a group specificity can convert substrates with the same functional groups. The alcohol hydrogenase converts, for example, alcohols such as ethanol and methanol into the corresponding aldehydes ethanal and methanal.

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Effect specificity of enzymes

Enzymes are not only substrate-specific, but also effect-specific. This means that a substrate that is bound to an enzyme can only be converted in a very specific way. Another enzyme can convert the substrate in a different way.

Enzyme activity

The enzyme activity describes how many substrate molecules an enzyme converts per minute. This depends on various factors such as substrate concentration, temperature and pH value.

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Substrate concentration

The enzyme activity depends on the substrate concentration.

The rate of conversion increases with increasing substrate concentration. This is because there are enough enzyme molecules to convert each substrate molecule. Therefore, the conversion rate initially increases proportionally to the substrate concentration.
If even more substrate molecules are added, the rate of turnover increases further, but not as quickly as before, since the free enzyme molecules are now becoming increasingly rare. Therefore, it takes longer for the substrate molecules and the free enzyme molecules to meet.
At some point the point has been reached at which all enzyme molecules are occupied and a further increase in the rate of turnover is no longer possible. So there is a maximum rate of turnover.

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Effect of temperature on enzyme activity

The enzyme activity is also dependent on the temperature. First, an increase in temperature also causes an increase in the conversion rate (principle of the RGT function). This is because the particles move faster at a higher temperature and thus they hit each other more quickly.
However, if the temperature is increased further, so-called heat denaturation occurs at some point, i.e. the tertiary structure of the enzymes is changed and they can no longer perform their function.
Therefore, there is an optimum temperature where the temperature is high enough for the particles to move quickly, but not yet high enough for denaturation to occur.

The influence of pH on enzyme activity

Another factor influencing enzyme activity is the pH value. Each enzyme has a pH at which it is most active. This pH value is the optimum pH of an enzyme. This is because proteins contain different groups that are protonated or deprotonated when the pH changes. This means that intermolecular interactions can be eliminated or additional interactions arise, which leads to a change in the tertiary structure.

Influence of inhibitors on enzyme activity

Inhibitors are substances that reduce enzyme activity and thus inhibit the functioning of enzymes. There are different inhibitors with different modes of action.

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Competitive inhibition

Inhibitors that cause competitive inhibition have a similar structure to the substrate. As a result, it can be reversibly bound to the active center of the enzyme and an enzyme-inhibitor complex is formed. In contrast to the substrate, the inhibitor cannot be converted by the enzyme and blocks the enzyme.
This type of inhibition can be removed by increasing the substrate concentration.

Non-competitive inhibition

Inhibitors that cause non-competitive inhibition bear no resemblance to the substrate. They are therefore reversibly bound not at the active site but at another point on the enzyme. This place is called the allosteric center. Binding to the allosteric center changes the spatial structure of the enzyme, which means that the substrate can no longer be bound to the active center.
In contrast to competitive inhibition, this type of inhibition cannot be canceled by increasing the substrate concentration.

Inhibition by heavy metal ions

The enzyme activity can also be inhibited by heavy metal ions (mercury, lead, copper ions, ...). The heavy metal ions can be irreversibly bound to the side groups (amino, sulfide, carboxy group, ...). This changes the intermolecular interactions and thus also the tertiary structure, which means that the substrate can no longer be bound to the enzyme.

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