Lock and Key Model

The lock and key model is used to describe the mechanism of enzyme action. This model was first proposed by German chemist Emil Fisher in 1894 to picturize the interaction of enzyme and substrate.

Enzymes play a vital role in regulating and controlling the biochemical process. The substrate binds to the enzyme at the active site and converted into products. A substrate is a substance that reacts with an enzyme and is transformed into a product.

The key step in the enzyme-catalyzed process is the binding of the correct substrate to the correct active site of the enzyme. Lock and key model explains substrate specificity of the enzyme in a biochemical reaction.

Diagram explains lock and key model of enzyme. Substrate A has the same shape as active site of enzyme, so it binds to the enzyme. While substrate B is unable to bind to enzyme due to different shape.

Key points of lock and key model

This model is based on the fact that as one specific key can open a specific lock, similarly one specific substrate can bind to one specific enzyme. This model is successful in clarifying the substrate specificity of an enzyme. The key points of this model are:

According to this model, the enzyme is a lock and the substrate is a key.
As the key has a similar shape to that of the keyhole of the lock, in the same manner, the substrate has a similar shape to the active site of the enzyme.
The substrate binds tightly to the active site of the enzyme, just like the key into its lock.
If the shape of the substrate and active site are not similar, the substrate will not be able to bind to the enzyme.
An enzyme is a rigid structure and the shape of the active site will not change or modify during the binding process.
This model explains single substrate binding to the active site of the enzyme.

Limitations of the lock and key model

There are some limitations in this model as it is unable to correctly explain some key points of the enzyme-catalyzed reaction.

This model does not explain the stabilization of the intermediate shape of the substrate.
According to this model, the enzyme is a rigid structure and does not change its shape upon binding, which is not supported by recent research. New research describes changes in enzyme shape upon binding with a substrate.
This model is unable to describe multiple substrate binding to the enzyme.

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Some questions and Answers

Q. What is lock and key in enzyme catalyzed reaction?
A. Enzyme is a lock and substrate is a key.

Q. Which enzyme characteristic is explained by lock and key model?
A. Substrate specificty of enzyme is explainde by this model.

Q. What are two limitations of lock and key model?
A. This model does not explain stabilization of intermediate shape of substrate and multiple substrate binding.

References

Habchi, J., Tompa, P., Longhi, S., & Uversky, V. N. (2014). Introducing protein intrinsic disorder. Chemical reviews, 114(13), 6561-6588.
Schneider, H. J. (2015). Limitations and extensions of the lock-and-key principle: Differences between gas state, solution and solid state structures. International Journal of Molecular Sciences, 16(4), 6694-6717.
Behr, J. P. (Ed.). (2008). The lock-and-key principle: the state of the art--100 years on (Vol. 17). John Wiley & Sons.
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Lock and Key Model | Key Points and Limitations