Principles of Biochemistry

8.2.1.2 Induced fit model

 

 

Experimental evidence indicates that many enzymes have flexibility in their shapes. They are not rigid and static; there is constant change in their shape. The induced fit model is used for this type of situation.

 

The induced fit model allows for small changes in the shape or geometry of the active site of an enzyme to accommodate a substrate. This model is a result of the enzyme’s flexibility; it adapts to accept the incoming substrate.

This model, gives an explanation for the active site properties of an enzyme because it includes the specificity of the lock and key model coupled with the flexibility of the enzyme protein.

 

The forces that draw the substrate into the active site are many of the same forces that maintain tertiary structure in the folding of peptide chains. Electrostatic interactions, hydrogen bonds, and hydrophobic interactions all help attract and bind substrate molecules.

For example, a protonated (positively charged) amino group in a substrate could be attracted and held at the active site by a negativity charges aspartate or glutamate residue.

Alternatively, cofactors such as positively charged metal ions often help bind substrate molecules.