What Is the Induced Fit Model of Enzyme Activity?

Enzymes are amazingly fast at catalyzing reactions and without them chemical reactions in the body would be considerably slower than they are. More than a century ago, in 1894, Emil Fischer proposed that enzymes worked their magic via a model called the lock and key model, which is still used today. However, a more precise model proposed by Daniel Koshland in the 1950s, the induced fit model, is also used.

The lock and key model describes a situation in which the enzyme and the molecule that it acts on in a reaction, the substrate, fit together perfectly. For this system to work, the enzyme has an active site, which is like a keyhole for the substrate. The substrate's shape, which is formed by the specific arrangement of atoms and bonds between the atoms, is like a key that fits exactly into the enzyme active site. This specificity means that like a house key, only the correct key will fit the lock.

The induced fit model is an elaboration on the basic idea of the lock and key model. In this model, though, the key and the enzyme active site do not fit perfectly together. Instead, the substrate interacts with the active site, and both change their shape to fit together. This still means that only particular substrates can fit each enzyme type though.

The basis of chemical reactions is a change in atom arrangement and bonds between atoms. When the substrate interacts with the enzyme it undergoes a chemical reaction that allows the atoms to move relative to each other, the bonds to possibly lengthen or shorten and the most reactive groups to move closer to each other, causing a shape change. This shape change makes the substrate more amenable to alteration, as it holds the substrate in a transitional state, which helps speed up the reaction that that enzyme catalyzes.

With the induced fit model, the way that the substrate has to change its structure may be useful in terms of the catalysis itself. It may represent the beginning of the reaction that the enzyme is catalyzing. Conversely, in the lock and key model, the catalysis follows after the substrate fits into the enzyme.