title: Role of sulfated tyrosines of thyroglobulin in thyroid hormonosynthesis.
abstract: Our previous studies showed that sulfated tyrosines (Tyr-S) are involved in thyroid hormone synthesis and that Tyr(5), the main hormonogenic site of thyroglobulin (Tg), is sulfated. In the present paper, we studied the role of Tyr-S in the formation and activity of the peroxidase-Tg complex. Results show that noniodinated (35)SO(3)-Tg specifically binds (Kd=1.758 microM) to immobilized lactoperoxidase (LPO) via Tyr-S linkage by using saturation binding and competition experiments. We found that NIFEY-S, a 15-amino acid peptide corresponding to the NH2-end sequence of Tg and containing the hormonogenic acceptor Tyr5-S, was a better competitor than cholecystokinin and Tyr-S. 35SO3-Tg, iodinated without peroxidase, bound to LPO with a Kd (1.668 microM) similar to that of noniodinated Tg, suggesting that 1) its binding occurs via Tyr-S linkage and 2) Tyr-S requires peroxidase to be iodinated, whereas nonsulfated Tyr does not. Iodination of NIFEY-S with [125I]iodide showed that Tyr5-S iodination increased with LPO concentration, whereas iodination of a nonsulfated peptide containing the donor Tyr130 was barely dependent on LPO concentration. Enzymatic hydrolysis of iodinated Tg or NIFEY-S showed that the amounts of sulfated iodotyrosines also depended on LPO amount. Sulfated iodotyrosines were detectable in the enzyme-substrate complex, suggesting they have a short life before the coupling reaction occurs. Our data suggest that after Tyr-S binding to peroxidase where it is iodinated, the sulfate group is removed, releasing an iodophenoxy anion available for coupling with an iodotyrosine donor.
authors.affiliation: Institut National de la Santé et de la Recherche Médicale Unité 555, Faculté de Médecine, Université de la Méditerranée, 27 Boulevard J. Moulin, 13385 Marseille, Cedex 05, France.
authors.forename: Marie-Christine
authors.initials: MC
authors.lastname: Nlend
authors.forename: David M
authors.initials: DM
authors.lastname: Cauvi
authors.forename: Nicole
authors.initials: N
authors.lastname: Venot
authors.forename: Odile
authors.initials: O
authors.lastname: Chabaud
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D007455:Iodine / Q000378:metabolism; D007784:Lactoperoxidase / Q000378:metabolism; D010446:Peptide Fragments / Q000378:metabolism; D009195:Peroxidase / Q000378:metabolism; D013431:Sulfates / Q000378:metabolism*; D013552:Swine; D013954:Thyroglobulin / Q000737:chemistry / Q000378:metabolism*; D013963:Thyroid Hormones / Q000096:biosynthesis*; D014443:Tyrosine / Q000737:chemistry / Q000378:metabolism*
chemical_list: D010446:Peptide Fragments; D013431:Sulfates; D013963:Thyroid Hormones; D014443:Tyrosine; D013954:Thyroglobulin; D007455:Iodine; D007784:Lactoperoxidase; D009195:Peroxidase