Participation of NADPH-cytochrome C reductase in thyroid hormone biosynthesis.

Purified rat liver NADPH-cytochrome c reductase supports iodination of tyrosine in a system including NADPH, cytochrome c and thyroid perioxidase. Catalase inhibits the iodination of tyrosine, while superoxide dismutase has no effect. Antibody developed in the rabbit against purified rat liver NADPH-cytochrome c reductase inhibits both reduction of cytochrome c and tyrosine iodination supported by the enzyme. The antibody forms a single precipitation line with thyroid extract, and inhibits NADPH cytochrome c reductase activity of the thyroid. The antibody partially inhibits iodination in a thyroid mitochondrial-microsomal fraction, but does not inhibit NADH-dependent iodination. The immunochemical studies indicate the participation of NADPH-cytochrome c reductase in thyroidal H2O generation, and the independent existence of NADPH-dependent and NADH-dependent H2O2 generation mechanisms in the thyroid.