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Steady state kinetics and regulation of thyroid peroxidase-catalyzed iodination.

Authors :
Nakamura M
Yamazaki I
Nakagawa H
Ohtaki S
Source :
The Journal of biological chemistry [J Biol Chem] 1983 Mar 25; Vol. 258 (6), pp. 3837-42.
Publication Year :
1983

Abstract

The kinetics of iodination of tyrosine and monoiodotyrosine was studied with purified hog thyroid peroxidase. The Lineweaver-Burk plots and stopped flow kinetic data both yielded a value of about 2 X 10(7) M-1 S-1 as the rate constant for reaction of Compound I with iodide. From Lineweaver-Burk plots, the rate constants for transfer of an assumed enzyme-bound iodinium cation to tyrosine, monoiodotyrosine, and GSH were estimated at 2.1 X 10(6), 3.3 X 10(6), and 3.9 X 10(7) M-1 S-1, respectively. This iodine-transferring reaction was stimulated by thyroxine, triiodothyronine, and diiodothyronine, and the effect increased with the decrease in the number of iodines in the molecules. Diiodotyrosine, during its coupling reaction, inhibited the iodinating reaction by changing the steady state intermediates of thyroid peroxidase from Compound I to Compound II. The quantitative relationship between iodinating and coupling activities of thyroid peroxidase is shown in a scheme, which suggests "preferential formation" of thyroxine from tyrosine by this enzyme system.

Details

Language :
English
ISSN :
0021-9258
Volume :
258
Issue :
6
Database :
MEDLINE
Journal :
The Journal of biological chemistry
Publication Type :
Academic Journal
Accession number :
6833233