The demonstration of protein-bound 99Mo-di- and trithiomolybdate in sheep plasma after the infusion of 99Mo-labelled molybdate into the rumen

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Abstract
1. Protein-bound, trichloroacetic acid- (TCA) insoluble 99Mo appeared in plasma a few hours after the introduction of 99Mo-labelled molybdate (30 mg Mo) into the rumen of sheep maintained on a basic diet supplemented with elemental sulphur (3 g S/d).2. Most of the 99Mo could be displaced from its protein carrier in vitro and the labelled compounds displaced were identified by Sephadex G-25 chromatography as di- and trithiomolybdate. Tetrathiomolybdate was not detected.3. In control experiments protein-bound, TCA-insoluble 99Mo predominated in plasma after the direct administration of [99Mo]tetrathiomolybdate, either into the rumen or intravenously. The 99 Mo could be displaced in vitro and [99Mo]tetrathiomolybdate identified, although [99Mo]trithiomolybdate was also present.The study provides direct evidence of thiomolybdate synthesis and absorption in ruminants in vivo.