Stimulation of protein-bound iodine formation by lipid extracts from hog thyroid microsomes

The lipid materials extracted from hog thyroid microsomes were found to contain factors which stimulated both the NADPH oxidation by NADPH-cytochrome c reductase and PBI formation by a reconstituted system containing the reductase as a hydrogen peroxide generator and thyroid peroxidase. For both reactions, the stimulating activity in the extracts from the other subcellular fractions was less than that observed in the extracts from microsomal fraction. Lipids extracted from hog liver microsomes did not show any NADPH oxidation stimulating activity. Thin-layer chromatography of the lipid extracts from thyroid microsomes revealed the presence of at least two stimulating factors differing in chromatographic behaviour. At least one of the stimulating factors separated on TLC stimulated the oxygen consumption accompanied by generation of hydrogen peroxide due to the NADPH oxidation by NADPH-cytochrome c reductase. From these results it was suggested that in thyroid microsomes, but not in liver microsomes, there were stimulating factors extractable by chloroform-methanol. The factors could stimulate NADPH oxidation by NADPH-cytochrome c reductase followed by generation of hydrogen peroxide, resulting in the enhancement of PBI formation coupled with thyroid peroxidase.