For many years, the interaction between a enzyme and its substrate was described by the model “key-lock”. However, studies have shown that this mechanism is flawed, which has led to a new model: a induced fitting theory.
According to the key-lock model proposed by Emil Fischer in 1894, an enzyme and its substrate are complementary. Enzymes present a specific region (active site) where the substrate fits. This fit occurs because of the bonds formed between the substrate and the amino acid side chains at the active site. It would be as if each substrate fits perfectly into a single enzyme, just as a key is used to open a particular lock (see figure below).
Look carefully at the key-lock model, in which the substrate fits perfectly into the active site
According to this model, both the enzyme and the substrate are rigid factors, that is, they do not have flexibility and, therefore, enzymatic reactions have high specificity. However, studies prove that enzymes have a certain flexibility, which allows for a conformational variety. Furthermore, some works prove that the substrate can induce such changes.
Given these findings, it was proposed to induced fitting theory (Induced Fit) by Koshland et al. in 1958. According to this theory, the substrate is capable of inducing a change in the conformation of an enzyme. This modification can be passed on to nearby enzymes, thus ensuring that they perform their catalytic role.
According to the induced fitting model, the substrate induces changes in the enzyme
The induced fitting theory therefore suggests that the interaction between enzyme and substrate is not as precise and simple a process as previously imagined. However, it is noteworthy that this model cannot explain the great specificity observed in enzymatic reactions.
By Ma. Vanessa dos Santos
Source: Brazil School - https://brasilescola.uol.com.br/biologia/teoria-encaixe-induzido.htm
