The hormones that are derivatives of amino acids, polypeptides or proteins are called peptide hormones. These being insoluble in lipids can not enter the target cell.
These act at the surface of target cell as primary messengers and bind to the cell-surface receptor forming the hormone-receptor complex.
It involves following steps
(i) Hormone called first messenger attaches to the cell surface receptor protein on the outer surface of plasma membrane of the target cell, forming a hormone-receptor complex.
(ii) This complex activates the enzyme adenyl cyclase.
(iii) Adenyl cyclase catalyses the conversion of ATP to cyclic AMP on the inner surface of plasma membrane.
(iv) cAMP serves as the second messenger or intracelluar hormonal mediator delivering information inside the target cells. This activates appropriate cellular enzyme system by cascade effect. Which induces the cell machinery to perform its specialised function.
(v) cAMP has a very short existence. it is rapidly degraded by the cAMP phosphodiesterase.
Water soluble hormones, such as amines, peptides, proteins and glycoproteins exert their control through the cyclic AMP These are quick acting hormones and produce immediate effect.
