Drug-Receptor Interaction VII

The insulin receptor protein represents
a ligand-operated enzyme , a
catalytic receptor. When insulin binds
to the extracellular attachment site, a
tyrosine kinase activity is “switched on”
at the intracellular portion. Protein
phosphorylation leads to altered cell
function via the assembly of other signal
proteins. Receptors for growth hormones
also belong to the catalytic receptor
class.
Protein synthesis-regulating receptors
for steroids, thyroid hormone,
and retinoic acid are found in the
cytosol and in the cell nucleus, respectively.
Binding of hormone exposes a normally
hidden domain of the receptor
protein, thereby permitting the latter to
bind to a particular nucleotide sequence
on a gene and to regulate its transcription.
Transcription is usually initiated or
enhanced, rarely blocked.