Question

Molecular weight of the smallest protein molecule ACTH (adrenocorticotropic hormone) is
(a) 5600
(b) 4500
(c) 3100
(d) 6200

Answer 1

Hint: It is the hormones that are released by the pituitary induce the synthesis of glucocorticosteroids by the adrenal cortex and the subsequent suppression of the immune system. The corticotroph cells of the anterior pituitary are responsible for synthesizing and secretion of the ACTH.

Complete answer:
ACTH is secreted by the anterior lobe of the pituitary gland and causes the increased production and release of cortisol by the cortex of the adrenal gland. The hormone is a polypeptide and it is formed by 39 amino acids and has the molecular weight of 4540 daltons. Mainly it is responsible for the secretion of glucocorticoid steroid hormones and also lipoprotein uptake by cortical cells.

Additional Information: ACTH is a 39-amino acid peptide. In mammals, its sequence is highly conserved since only amino acids 31 and 33 vary between higher mammals and primates. The biological activity of the ACTH molecule basically depends on its first 24 amino-terminal amino acids while fragments of less than 20 amino acids long are completely inactive. Although, the residue 25-39 is important for the stability of the molecule, increasing its otherwise short half-life.
So, the correct answer is ‘4500’.

Note: Truncation of ACTH from the C-terminus gradually reduces its activity while removal of the four basic residues (Lys–Lys–Arg–Arg) in positions 15–18 inactivates it completely. During post-translational modification, the secretion of ACTH is under the control of corticotropin-releasing hormone (CRH) and to a lesser degree to arginine vasopressin (AVP).