A thyrotropin-like molecule from the pituitary of an Indian freshwater murrel: comparison of its biological activity with other thyrotropins

Partha Roy ; Department of Physiology, University of Turku, Kiinamyllynkatu 10, FIN 20520, Turku, Finland

Abhijit Chatterjee ; Endocrinology Laboratory, Institute of Zoology, Academia Sinica, Nakang, Taipei, Taiwan

Partha Pratim Banerjee ; John Hopkins University, Division of Reproductive Biology, School of Hygiene and Public Health, Baltimore, MD 21205-2179, USA

Samir Bhattacharya ; Department of Zoology, Visva Bharati University, Santiniketan-731 235, West Bengal, India- samir@vbharat.ernet.in

Abstract

Murrel pituitary thyrotropin-like molecule (mTSH) was purified to homogeneity with the help of a convenient and sensitive in vitro assay system where addition of this material to the thyroid follicle incubation stimulated thyroxine (T4) secretion into the medium. Pituitary extract of a freshwater murrel, Channa punctatus, was solvent extracted to obtain glycoprotein enriched fraction. This was subjected to Sephadex G-100 gel filtration and eluate of void volume (peak I) showed strong TSH activity (as reflected from T4 secretion) which was further purified by using concanavalin A-Sepharose, FPLC Mono Q and immunoaffinity chromatography. Purified mTSH gave a single band in PAGE, and SDS PAGE revealed two dissimilar subunits, alpha and beta. Addition of increasing concentrations of mTSH, Indian carp TSH (cTSH) and bovine TSH (bTSH) to in vitro murrel thyroid follicle incubations caused a linear increase in thyroxine (T4) release into the medium, effect was highest with mTSH and lowest with bTSH. However, in in vivo experiments, injections of increasing doses of mTSH to murrel elevated plasma T4 level in a linear manner while bTSH gave a biphasic response. Addition of mTSH and bTSH to rat or goat thyroid epithelial cell incubations equally stimulated T4 release into the medium, while cTSH had significantly less effect. Binding affinity (Ka) and receptor occupancy (Bmax) of mTSH to murrel thyroid follicular membrane preparation was considerably higher in comparison to cTSH or bTSH whereas both mTSH and bTSH had nearly similar Ka and Bmax with rat thyroid epithelial cell membrane preparation. Findings indicate that mTSH is a more potent TSH as compared to carp and bovine TSH in murrel and has equipotent biological activity as bTSH on rat and goat thyroid.

Acknowledgement and Source(s)

This Abstract was originally published in: Science direct . The article itself is published under the above title in Comparative Biochemistry and Physiology Part C: Pharmacology, Toxicology and Endocrinology . Volume 125, Issue 2 , February 2000, Pages 165-177. The copyright of the text is still with the copy right owners in full amount.

HOME of this page