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The extrathyroidal conversion of T4 to T3 in the striped racer snake, Elaphe taeniura

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Abstract

The extrathyroidal conversion of thyroxine to triiodothyronine in the snake, Elaphe taeniura, has been determined in vitro. The liver, kidney and pancreas are important organs showing significant 5′-deiodinase activity. The pancreas has a higher conversion rate (18.5±3.58 pmol·min-1·mg protein-1) than other vertebrate tissues that have been studied. The 5′-deiodinase activity is dependent on substrate (thyroxine) concentration, cofactor, i.e. dithioerythritol concentration, temperature, duration of incubation and pH. It is sensitive to iopanoic acid, propylthiouracil, salicylate and propranolol. It is also indicative that the 5′-deiodinase activity increased and decreased, respectively, in snakes with experimentally induced hyper- and hypo-thyroidism. These characteristics suggest that snake 5′-deiodinase is similar to that of mammals, probably of type I category.

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Abbreviations

ANOVA:

analysis of variance

BSA:

bovine serum albumin

BW:

body weight

cpm:

counts per minute

5′D:

5′-deiodinase

DTE:

dithioerythritol

EDTA:

ethylenediamine tetraacetate

IOP:

iopanoic acid

K m :

Michaelis-Menten constant

L/D:

Light/Dark

MW:

molecular weight

NRS:

normal rabbit serum

PEG:

polyethylene glycol

%B:

percentage of added label found in the pellet

PTU:

propylthiouracil

RIA:

radioimmunoassay

rT3 :

3,5,5′-triiodothyronine

SPSS:

Statistical Package for the Social Sciences

T3:

3,5,3′-triiodothyronine

T4:

thyroxine

TRIS:

Tris (hydroxymethyl) aminomethane

Tx:

thyroidectomized

V max :

maximum velocity of enzyme reaction

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Authors and Affiliations

  1. Department of Physiology, The Chinese University of Hong Kong, Hong Kong

    C. C. Wong

  2. Department of Biology, The Chinese University of Hong Kong, Hong Kong

    K. Y. Lam & K. W. Chiu

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  1. C. C. Wong
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  2. K. Y. Lam
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  3. K. W. Chiu
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Wong, C.C., Lam, K.Y. & Chiu, K.W. The extrathyroidal conversion of T4 to T3 in the striped racer snake, Elaphe taeniura . J Comp Physiol B 163, 212–218 (1993). https://doi.org/10.1007/BF00261667

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  • DOI: https://doi.org/10.1007/BF00261667

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