The inhibition of bovine ceruloplasmin oxidase activity by thiomolybdates in vivo and in vitro: a reversible interaction.

The administration of pharmacological doses (greater than 100 mg Mo) of trithiomolybdate or tretrathiomolydbate to ruminants causes a transient apparent decrease in the ceruloplasmin oxidase activity of plasma and a more persistent increase in copper bound to plasma albumin. Sephadex gel-filtration and/or dilution of "inhibited" samples taken from an infused animal or of plasma treated with thiomolybdate in vitro restores activity back to pretreatment levels. The increase in albumin bound copper does not appear to be related to ceruloplasmin breakdown. It is concluded that, contrary to a recent report, the inhibition of ceruloplasmin oxidase activity is reversible and thus unlikely to be of pathological relevance, since circulatory thiomolybdate concentrations in molybdenotic animals are likely to be very low. It is recommended that thiomolybdate preparations used for in vitro and in vivo studies should be carefully purified by Sephadex chromatography.