Effect of molybdenum treatments on the distribution of Cu and metallothionein in tissue extracts from rats and sheep

An examination was made of the effects of tetrathiomolybdate (TTM), ammonium molybdate (AM), sodium sulphide, and two molybdo amino acids (cysteine-Mo, cysteine-Mo-S) on the distribution of Cu and Zn among proteins in extracts of the livers and kidneys of rats and sheep. Tetrathiomolybdate caused a shift in the chromatographic distribution of Cu from low molecular weight proteins such as metallothionein (MT) to proteins of higher molecular weight (greater than 100,000 daltons). This was not due to polymerization or cross-linking of metallothionein with the latter, but to the formation of protein-TTM complexes that had a strong affinity for Cu. There was a concomitant redistribution of Zn towards proteins of low molecular weight. Pretreatment of high molecular weight proteins from rat liver with TTM greatly increased the capacity of the proteins to remove Cu from MT. When AM or sodium sulphide were added together to extracts of rat liver, changes similar to those induced by TTM were observed in the chromatographic distribution of Cu and Zn. Individually, these compounds had no significant effect on the distribution of the metals. Of the two molybdo amino acids, only cysteine-Mo-S altered the chromatographic distribution of Cu in extracts of rat liver. The redistribution was in the same direction as that induced by TTM, but was not as pronounced.