Answer
Peptide hormones interact with receptor proteins in the plasma membrane of cells.
The term peptide hormone includes hormones that are chemically peptides ( oxytocin and ADH), proteins ( insulin and glucagon), glycoproteins ( FSH and LH), and modified amino acids ( T3, T4 and epinephrine).
Work Step by Step
The term peptide hormones includes not only hormones that are chemically peptides but also proteins, glucocorticoids, and modified amino acids that are hormones .
First messenger.
When the peptide hormone contacts its target it acts as a so-called first messenger. It bind to a protein receptor in the plasma membrane, but it usually never enters the cell. When the hormone (e.g. epinephrine, binds to its surface receptor, this activates an enzyme that cleaves ATP and results in the formation of c-AMP-- the so called second messenger. Cyclic AMP activates a protein kinase enzyme in the cell and this activates other enzymes in a series of reactions ( * an enzymatic cascade) one after another-- each enzyme being used more than once in the cascade. The results --in this case--in glycolysis and in the release of many molecules of glucose which enter into the blood and raise the blood glucose level.
* Some enzymes active in this cascade are protein kinase A and B; phosphorylase kinase A and B; and glycogen phosphorylase A and B
