Effects of dietary molybdenum and sulphur on the distribution of copper in plasma and kidneys of sheep.

1. A 30-week study has been made in growing ewe lambs of the effects of dietary supplementation with molybdenum, or Mo plus inorganic sulphate on the distribution of copper in their blood plasma and kidneys. 2. The addition of 25 mg Mo and 5 g SO42-/kg diet increased Cu concentrations in plasma and kidney and decreased those in liver. Plasma caeruloplasmin activities (ferroxidase; EC 1.16.3.1) were unaffected. 3. Subcellular fractionation of the kidney cortex and gel filtration of the plasma and kidney cortex cytosol showed that the increased Cu content of these tissues was associated with abnormalities in the distribution of Cu. It appeared that both Cu and Mo were associated with the same proteins. 4. Dietary supplementation with Mo alone (25 mg/kg) had no effect on plasma or kidney Cu concentrations, suggesting that S metabolism is involved in the formation of the abnormal Cu-binding proteins in plasma and kidney. 5. The results are discussed in relation to the induction of Mo-induced Cu-deficiency states and the possible involvement of thiomolybdates.