How are enzymes related to biochemistry?

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The enzyme-substrate complex

The first step in enzymatic catalysis is the formation of an enzyme-substrate complex. In the active center of the enzyme there is a close spatial association of the reactive groups of the enzyme and the substrate. Hydrogen bonds, van der Waals forces or covalent bonds contribute to the temporary stable binding of the substrate to the enzyme; a transitional state is formed. This enables the catalytic reaction. In principle there are two possibilities for the interaction between enzyme and substrate: the classic lock-and-key principle and the newer model of the induced fit. The lock and key principle only illustrates the specificity of an enzyme. Technical investigations of the molecular structure of enzyme and substrates, on the other hand, have shown that the dynamic processes involved in the binding of enzyme and substrate are more in line with the induced fit model.

The lock and key principle

Enzymes are highly specific with regard to the catalyzed reaction and the selection of the reaction participants, the substrates. Normally, an enzyme catalyzes only a single chemical reaction or a series of closely related chemical reactions. Side reactions in which useless by-products could be formed do not take place. The specificity of an enzyme for a substrate is very high and in many cases absolute; the substrate fits into the enzyme molecule like a key in its lock.

The induced-fit mechanism

When the substrate binds to the enzyme, the enzyme-substrate complex is formed, the first step in enzymatic catalysis. The substrate binds to the active center of the enzyme molecule. The catalytic activity of the enzymes and their regulation depends primarily on the specificity of the binding of the substrate to the active center.

The active center is the region in which all chemical groups that are involved in the reaction to be catalyzed are brought into spatial contact. In some enzymes, the active center only takes on the complementary form after the substrate has been bound. This process of dynamic detection is called induced fit.


An example of the induced-fit mechanism is the enzyme hexokinase.