Enzymes are specific!
- Specificity of enzymes
Intermediate interaction between enzymes and its substrates occurs through molecular recognition based on complementary structure. This specific site on enzymes where the substrate and enzyme bond is a cleft called the active site . At this site the complementary substrate bonds using hydrophobic, electrostatic and van der waals interactions as well as hydrogen bonding.
Types of specificity
Relative specificity – enzymes to substrates that contain similar structures and the same type of bonds
Absolute specificity – enzymes only catalyse one reaction
Group specificity – enzymes only bind to n=molecules that have a specific functional group
Linkage specificity – enzymes only bind to a particular kind of chemical bond, regardless of structure of molecule
Stereochemical specificity – enzymes bind to certain steric or optical isomers
Hypotheses of Enzyme-Substrate Interactions
- Fischer’s lock and key hypothesis (Emil Fischer 1894)
This theory states that the substrate (key) is perfectly complementary to the active site (lock). Only if the substrate fits perfectly would it be catalysed, showing that enzymes can only catalyse specific substrates.
- Kushland’s induced fit hypothesis
Although the both theories are recognized, the induced fit is the more accurate of the two.the induced fit hypotheses explains that the shape of the enzyme molecule changes to fit the shape of the substrate when they encounters , thereby enabling the substrate to bind more effectively.