Biological Chemistry - Berezov T. T., Korovkin B. F. 1998

Hormones
Pituitary Hormones
Adrenocorticotropic hormone (ACTH, corticotropin)

As early as 1926, it was established that the Pituitary Gland exerts a stimulating effect on the Adrenal Glands by increasing the secretion of Hormones from the adrenal cortex. Data accumulated to date indicate that this property is possessed by ACTH, which is produced by the basophilic Cells of the adenohypophysis. In addition to its primary action—stimulating the Synthesis and Secretion of Adrenocortical Hormones—ACTH exhibits fat-mobilizing and melanocyte-stimulating activities.

The ACTH molecule contains 39 amino acid residues across all animal species. The Introduction/19.html">Primary Structure of porcine and ovine ACTH was deciphered back in 1954–1955. Below is the refined structure of human ACTH:

Class="center">Н-Сер-Тир-Сер-Мет-Глу-Гис-Фен-Арг-Трп-Гли-Лиз-Про-Вал-Гли-Лиз-Лиз-Дрг-Дрг-Про-Вал-Лиз-Вал-Тир-Про-Асп-Ала-Гли-Глу-Асп-Глн-Сер-Ала-Глу-Ала-Фен-Про-Лей-Гпу-Фен-ОН

Differences in the ACTH structure among sheep, pigs, and cattle pertain only to The Nature of the 31st and 33rd amino acid residues; nevertheless, all of them exhibit nearly identical biological activity, much like human pituitary ACTH. In the ACTH molecule, as in other protein hormones, although active centers akin to those of Enzymes have not been discovered, the presence of two active regions within the peptide chain is postulated: one responsible for binding to the corresponding receptor, and the other for the hormonal effect.

Data concerning The Mechanism of ACTH action on steroid hormone synthesis indicate a vital role for the adenylate cyclase system. It is hypothesized that ACTH interacts with specific receptors on the outer surface of The Cell membrane (these receptors consist of Proteins complexed with other molecules, notably sialic acid). The signal is subsequently transmitted to the adenylate cyclase enzyme, located on the inner surface of the cell membrane, which catalyzes The breakdown of ATP to form cAMP. The latter activates protein kinase, which in turn, via an ATP-dependent process, phosphorylates cholinesterase, converting Cholesterol esters into free cholesterol; this free cholesterol is then transported into the adrenal Mitochondria, which house all the enzymes catalyzing The conversion of cholesterol into corticosteroids.