Some properties of a unique cadmium-binding moiety in the soluble fraction of rat testes.

A 30,000 molecular weight testicular Cd-binding peak (30,000 MW Cd-BP) previously implicated in Cd-induced testicular injury was unstable during storage with respect to apparent molecular weight determined by Sephadex G-75 chromatography. Storage of testicular cytosol labeled with 109Cd in vivo or in vitro for several days at 4 degrees C under nitrogen resulted in disappearance of the 30,000 MW Cd-BP and increased 109Cd uptake in other protein fractions. Rechromatography of the previously isolated 30,000 MW Cd-BP after storage gave rise to a 109Cd peak eluting in the higher molecular weight region. The latter effect was prevented by 1 mM dithiothreitol, suggesting that sulfhydryl groups were involved in the apparent aggregation. The 30,000 MW Cd-BP found in testes of rats was not present in testes of roosters, nor in liver and kidney of either species, providing further evidence of a correlation between the occurrence of 30,000 MW Cd-BP protein in the tissue and susceptibility to Cd-injury. The inability of parenterally administered HgCl2 to induce testicular injury compared to the same dose of CdCl2(0.011 mmol/kg) is apparently related to the poor uptake of Hg in the testes (one-eighteenth that of Cd) rather than to an inability of Hg to bind to the 30,000 MW Cd-BP. Our studies indicate that binding of Cd to this unique 30,000 MW testicular component, as yet unidentified, is a possible basis for the unique sensitivity of the testis to Cd injury.