EXPORT CITATION

Chapter-44 Mechanisms of Action of Hormones

BOOK TITLE: Textbook of Biochemistry for Medical Students

Author
1. Vasudevan DM
2. S Sreekumari
3. Vaidyanathan Kannan
ISBN
9789350250167
DOI
10.5005/jp/books/11359_44
Edition
6/e
Publishing Year
2011
Pages
8
Author Affiliations
1. Faculty of Medicine, Amrita Vishwa Vidyapeetham, (Amrita University), Kochi, Kerala, Formerly Principal, College of Medicine, Amrita, Kerala; Formerly, Dean, Sikkim Manipal Institute of Medical Sciences, Gangtok, Sikkim, Amrita Vishwa Vidyapeetham (Deemed University), Cochin, Kerala, E-mail: dmvasudevan@aims.amrita.edu, PG Programs and Research College of Medicine, Amrita Institute of Medical Sciences, Kochi, Kerala, India, College of Medicine, Amrita Institute of Medical Sciences, Kochi, Kerala, India; Sikkim Manipal Institute of Medical Sciences, Gangtok, Sikkim, India
2. Jubilee Mission Medical College, Trissur, Kerala, Sree Gokulam Medical College and Research Foundation, Thiruvananthapuram, Kerala, India, Jubilee Mission Medical College and Research Institute, Thrissur, Kerala, India, Government Medical College, Thrissur and Thiruvananthapuram, Kerala, India; Sree Gokulam Medical College and Research Foundation, Thiruvananthapuram, Kerala, India; Jubilee Mission Medical College and Research Institute, Thrissur, Kerala, India
3. Amrita Institute of Medical Sciences, Kochi, Kerala, India, Pushpagiri Institute of Medical Sciences and Research Centre, Thiruvalla, Kerala, India, Believers Church Medical College and Hospital, Thiruvalla, Kerala, India
Chapter keywords

Abstract

Definition of a hormone is that is synthesized by one type of cells and transported through blood to act on another type of cells. G protein is a peripheral membrane protein consisting of alpha, beta and gamma subunits. When GTP is attached, it becomes active. It then activates the enzyme adenylate cyclase. G proteins are used for different signal transduction pathways. There are 2 major types of G proteins; Gs (G stimulatory) and Gi (G inhibitory). G protein activity can be inhibited by GTPase. Examples of hormones that use cyclic AMP as second messenger are ACTH, FSH, LH, PTH, etc. Example of a hormone that uses cGMP as second messenger is ANF. Examples of hormones that use calcium or PIP2 as second messenger are TRH, GnRH, CCK, etc. Examples of hormones whose actions are mediated via a tyrosine kinase mechanism are Insulin, EGF, PDGF, NGF, etc. Cholera toxin binds to a ganglioside on intestinal mucosal cell, which leads to ribosylation of the alpha subunit of Gs protein. Pertussis toxin ribosylation the alpha subunit of Gi protein and prevents the Gi-GDP complex from interacting with the activated receptor. Diacylglycerol (DAG), the second messenger formed by the hydrolysis of PIP2 activates protein kinase C which in turn phosphorylates other target proteins. Hormones bind to the specific area of the gene, referred to as the hormone response element (HRE), e.g. Thyroid hormones and steroid hormones.

© 2019 Jaypee Brothers Medical Publishers (P) LTD.   |   All Rights Reserved