Formation of lodinated Protein in Saliva

Abstract

AFTER intravenous injection of tracer amounts of iodine-131 in the dog, the concentration of iodine in the parotid saliva is 5–20 times that in the plasma. A variable proportion (1–95 per cent, but commonly 10–30 per cent) of this iodine is non-dialysable and is precipitated by common protein precipitants, such as 5 per cent trichloroacetic acid, zinc hydroxide, tungstic acid, and 66 per cent acetone or ethanol. None of the activity in the precipitate is extractable by n-butanol, unlike the protein-bound radioactivity of plasma. After hydrolysis of the protein with pancreatin, paper chromatography in a butanol/acetic acid/water system (4 : 1 : 1) revealed radioactivity almost entirely in monoiodotyrosine with only a small amount in diiodotyrosine; there was no sign of labelled iodothyronines. Evidently the organic iodide in saliva is in the form of iodotyrosines linked by peptide bonds into proteins. Formation of protein-bound iodine was completely and immediately prevented by injection of thiouracil or mercaptazole in doses of 5 mgm./kgm. or more, but was not modified by total thyroidectomy.