Enzymes and receptors are quite different in their purpose in the body.
But they both are proteinacious in nature and help to regulate body physiology.
Yet, structurally and functionally they are much different.
By function both can be described as.
Receptors are signal receivers and form the front end of messenger communication system. They evoke and bringing changes in the body physiology when a ligand binds to them.
In pharmacology, few enzymes act as receptors and even few receptors have enzymes withing them.
See types of receptors for an idea.
Lets describe the similarities between enzymes and receptors:
Enzymes and receptors are similar in the following ways like
- Inertness: Both are by themselves inert and can produce an effect only in presence of a substrate or ligand respectively.
- Targets: Both can act as targets for drug molecules. For examples lisinopril is given to control high blood pressure by inhibiting the enzyme angiotensin converting enzyme. While metaprolol is used to control blood pressure by acting on β-receptors.
- Reaction kinetics: Both functions can be described by kinetic equations like rate of association and dissociation constants. As long as enzyme is bound to substrate, there is a product formation and when substrate dissociates from enzyme no product is formed. Similarly, as long as ligand is bound to receptor, there is response. When ligands dissociates, there is no further response from receptors.
- Degree of response: The concentration of enzymes and receptors matter. Decrease in concentration than required can give sub-maximal responses when stimulated by substrate or ligand respectively.
- Competitors: Their actions can be controlled by competitors for binding. I.e. a substrate which binds to enzyme and ligand which binds to receptor can be displaced by a competitive binder. Thus the action of enzyme and receptors can be manipulated.
- Inhibitors: Function of enzyme and also receptors can be blocked by respective inhibitors. These inhibitors bind to enzyme and receptors and prevent the original ligands from binding and evoking a response.
- Allosteric binding sites: Allosteric binding site is a site on the enzyme or receptors which is adjacent to actual binding site. These sites can help in controlling the overall response of the enzyme or receptors in positive or negative way. Though the actual substrate or ligand binds, its response will be influenced by the molecule bound to allosteric site.