Biosynthesis and regulation of iodolipids in calf thyroid

The incorporation of 125I into iodolipids was investigated in calf thyroid slices. Time course studies showed that the iodination of lipid reaches a plateau after 30 min of incubation. A highly significant correlation was found between iodination of lipid and of protein (r = 0.906), suggesting that both reactions may be related. Addition of PTU or MMI caused a significant inhibition of lipid iodination, indicating that a peroxidase could be involved in this reaction. The iodinated lipids are not attached to protein, since they migrated in BEA chromatography and pancreatin digestion of the samples did not modify the percentage radioactivity. The iodolipid fraction observed in BEA chromatography was eluted and analysed by TLC. Iodinated free fatty acids and neutral lipids comprised most of the radioactivity. Although iodolipids are present in every subcellular fraction, the 20 000 X g pellet had the greatest proportion of iodinated fatty acids and neutral lipids.