The characteristics of hormone binding to receptors are:
① High affinity
HR=H+R
The affinity between hormone (H) and receptor (R) can be expressed by its dissociation constant Kd.
Kd=[H][R]/[HR]
The range of Kd is10-9—10-11mol/l.
The smaller the Kd, the higher the affinity and the lower the hormone concentration, and the hormone can also bind to the receptor and cause
Biological effects.
② High specificity
This property is determined by the binding domain of the receptor and the structural site of the ligand, as well as the conformation of the receptor and ligand. Only target cells with corresponding receptors will respond to hormones. Cells without corresponding receptors are also exposed to hormones, but they do not cause reactions. The relationship among cytokines, neurotransmitters and their receptors is similar.
③ The combination of hormone and receptor is non-valence and reversible.
When the hormone is separated from the receptor, the messenger function of the hormone stops.
④ The number of intracellular receptors is very large.
There are usually hundreds to thousands or even tens of thousands. The biological effect of hormones is usually proportional to the amount of hormones bound to the same receptor, but when the concentration of hormones rises to a certain concentration, the binding curve between hormones and receptors is saturated due to the limited number of receptors. After the receptor is saturated, the biological effect of hormones will no longer increase with the increase of hormone concentration.