Studies on the Biosynthesis of Thyroid Hormone: Reconstruction of a Definedin VitroIodinating System

Abstract
The ability of NADPH to stimulate tyrosine iodination in thyroid cell particles is correlated with NADPH-cytochrome c reductase activity in the preparations. Heat and pchloromercuribenzoate depress both functions in parallel. Vitamin K3 stimulates iodination and is synergistic with NADPH. NADP-cytochrome c reductase was purified from calf thyroid tissue. An in vitro iodinating system was reconstructed from partially purified enzymes utilizing the soluble iodide peroxidase-tyrosine iodinase, NADPH, the purified reductase, and vitamin K3 or cytochrome c. Reductase supported iodination was catalase sensitive. NADPH-cytochrome c reductase may be involved in endogenous generation of peroxide utilized in the iodination reaction. (Endocrinology88: 486, 1971)

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