Changes in the binding of copper in the plasma of molybdenum supplemented rats.

After incubating plasma of Mo-supplemented rats (Mo-plasma) with 64Cu only part of it could be removed by dialysis against EDTA or histidine or by treatment with dithiocarbamate; this nondialyzable Cu was shown to be bound to albumin. The maximal amount of 64Cu bound this way equaled the Mo-induced increase in total plasma Cu. After addition of stable Cu, dialysis of Mo-plasma against a histidine solution showed that no extra Cu became tightly bound, suggesting that the 64Cu binding was due to an exchange between added 64Cu and stable Cu already present. Incubating Mo-plasma with Hg compounds prevented 64Cu binding and released stable Cu, indicating that Cu in Mo-plasma was sulfhydryl bound. Part of the Mo in Mo-plasma was freely dialyzable. The remaining part was shown to be SH bound as well. The estimated atomic ratio of SH-bound Cu and Mo was unity. Molybdenum increased the number of SH groups in plasma, and for each Cu atom at least one SH group was calculated to be present.