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Introduction
The lock-and-key approach, which is also used to explain the enzyme-substrate interaction, is in direct opposition to this concept. Using this approach, both the substrate and the enzyme’s active site undergo conformational changes until the substrate is entirely attached to the enzyme, at which time the final shape and charge of the enzyme are determined. This causes the enzyme to become active and begin performing its catalytic job.
Daniel Koshland proposed the induced-fit model in 1958, and it has been in use ever since. The lock-and-key model of the enzyme-substrate complex is less widely recognised than the kinetic model. Using this approach, the interaction between the substrate and the enzyme is akin to a key (the substrate) that is very specific to the lock (the enzyme) (the active site of the enzyme). It shows a sort of engagement that is immobile and rigid in nature. Instead of being a rigid structure, the induced fit model demonstrates that enzymes are very flexible structures, with the active site constantly reshaping as a result of interactions with the substrate, until the substrate is completely bound to the enzyme.
Difference Between Lock and Key Model and The Induced Fit Model
When considering how substrates may bind in an enzyme’s active site, the lock-and-key model and the induced-fit hypothesis are two alternative theories to consider.
A key (the substrate) fits perfectly into a lock, according to the lock-and-key concept, which implies that the substrate’s form is totally complementary to the active site and so fits in ‘perfectly’ (the enzyme). When the substrate binds to the active site, there is no change in the geometry of the active site. We must always keep in mind, however, that the induced-fit hypothesis is very similar to the lock-and-key model, albeit with a few minor differences.
Although the substrate and active site are not totally complimentary, there is still some complementarity between them, according to this theory. When you compare the enzyme and its active site with a hand (the substrate), you’ll notice that they’re similar in shape but not exactly the same size and shape. When the hand is inserted into the glove, the glove changes shape slightly and moulds itself to the hand, ensuring that it fits tightly around the hand.
Additionally, the active site alters shape to securely attach to the substrate in the same way. There is a great deal of evidence to support this hypothesis at the moment. When it comes to catalysing reactions with several substrates, some enzymes are capable of doing so while maintaining a consistent structure between the diverse substrates. This is comparable to how a single glove may be worn by multiple people with varying hand shapes (since hands are often similar in shape!).
Induced Fit Model
After all, the induced fit model continues to maintain that enzyme substrates are not exactly fitted to the active sites of their respective enzymes before binding takes place (the opposite was the lock and key model, proposed by a man named Emil Fisher; this model was widely accepted for quite a while, but did not explain the changes that occurred during the process of catalysis).
According to the model, the interactions between the substrates and the binding sites are rather modest at the beginning of the simulation. It is believed that initial binding of the substrate generates a change in the conformational state of the binding site, causing it to assume the proper shape for binding with the rest of the substrate. This model is also referred to as the hand-in-glove model, which refers to the analogy of a hand changing the shape of a glove as it is put on, progressively making it easier for the hand to fit within the glove over time.
Lock and Key
An enzyme’s active site and its substrate are represented by the lock and key model, which is a representation of the interaction between the two. The concept is that the active site, which is commonly depicted as an invagination of the protein, is similar to a tunnel that is open to the outside environment (To leave a passage to the substrate). It should be noted that because this tunnel is constructed by the aminoacids of the protein, it is not a smooth tunnel, but rather more like the opening of a lock; the electronic density of the atoms of the protein is disposed so that only a specific substrate can pass through the tunnel, similar to how only the correct key can pass through the opening of a lock.
As a result, the parallel with the lock and key comes into play here. It isn’t used very much anymore because it has various flaws, thus it isn’t very effective. Consider the following example: An enzyme can have numerous substrates at the same time.
When the substrate attaches to the protein, the protein’s conformation must change.
The substrate is not a rigid key, but rather a molecule that rotates a great deal around the bonding site.
So, actually, instead of the lock and key model, it’s preferred the glove and the hand model. This occurs when the glove represents the active site of a protein enzyme and the hand serves as a representation of the substrate. For example, you cannot wear a glove in your nose, but the glove does not look exactly like a hand when there isn’t a hand around; you can see that the active site is pictured as it modifies its conformation when it binds to the substrate, but it maintains the specificity for the substrate even if the active site isn’t bound.
Conclusion
The term “induced fit” refers to the ability of the protein’s active site to change shape at the active site in order for the substrates that enter to fit. When the substrates access the active site and the form is appropriate for them, as shown in the diagram in question 22, this occurs. The theory of induced fit is the most generally recognised and applied. The induced fit mechanism is the most widely accepted because it is a development of the lock and key mechanism in that it suggests that the enzyme’s active site changes slightly in order for the substrate to fit, whereas the lock and key mechanism does not suggest that the active site changes at all.
