Receptors -Introduction and type of bonding

 Introduction

The receptor concept was formulated by John. N. Langley in 1907 ( Worked on the antagonism of atropine and Pilocarpine)

Drugs that interact with receptor are most important in medicine and provide treatment for ailments such as (3PDHA)
Pain
Parkinson's disease
Psychosis
Depression
Heart failure
Asthma & Many other problems
There are large numbers of different receptors in the body that interact with different chemical messengers
For example - Acetylcholine - Cholinergic receptor
Dopamine - Dopaminergic receptor
γ-aminobutyric Acid - GABA receptor
Epinephrine - Adrenergic receptor

The various receptors show selectivity for one chemical messenger over another because they have a binding site of different shapes, structures, and amino acids.
However, receptors that interact with one specific chemical messenger are not identical.

Drug - receptor interaction involves one or more of the following type of bonding-
1. Covalent bond
2. Ionic bond
3. Hydrogen bond
4. Hydrophobic interaction

1. Covalent bond

  • Two atoms one from the ligand and one from the receptor share a pair of electrons.
  • Strongest bond
  • Significant strength-50-150 Kcal/mol due to this, it results in irreversible binding with receptors, leads to the destruction of the receptor.
Example - Acetylcholinesterase is irreversibly inactivated by a no of phosphate esters blocking of α -adrenoreceptor by phenoxybenzamine.

2. Ionic bond
  • When two ions of opposite charge are attracted to each other through electrostatic force.
  • Strength- varies between 5-10 Kcal/mol and decreases proportionally to the square of the distance between the 2 atoms.
  • The ability of the drug to receptor binding by ionic bond increases as the drug molecule diffuses closure to the receptor.

3. Hydrogen bond

  • This type of bond present between drug and receptor
  • Weak and broke easily
  • Many drugs contain hydroxyl, amino carboxyl, and carbonyl group they can from H bond with receptors
  • A single H bond can not support drug-receptor interaction but multiple H bonds formed between drug and receptor result in significant stability.
  • H bonding is an essential requirement for much drug-receptor interaction.
4. Hydrophobic interaction
  • When two non-polar groups such as the lipophilic group on the drug and the non-polar group in the receptor each surrounded by ordered water molecule it becomes a disorder, results in a decrease in the free energy that stabilizes the drug-receptor complex.
  • It is a reversible type of bonding that liberates energy.
  • When two non-polar groups such as the lipophilic group on the drug and the non-polar group in the receptor each surrounded by ordered water molecule it becomes a disorder, results in a decrease in the free energy that stabilizes the drug-receptor complex.
  • It is a reversible type of bonding that liberates energy.




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