Hepatic copper- and zinc-binding proteins in ruminants. 2. Relationship between Cu and Zn concentrations and the occurrence of a metallothionein-like fraction.

In the previous paper (Bremner & Marshall, 1974) the effects of variations in copper and zinc status of ruminants on the distribution of the metals among soluble hepatic proteins were described. Three fractions ( I-3), with approximate molecular weights of 3 7 j ooo,35 ooo and I z 000, were isolated by gel filtration on Sephadex G-75 but none of these was fully characterized. The distributions of the Cu and Zn were closely related as, for example, Zn was absent from, or present in only low concentration in fraction 3 in high-Cu as well as in Zn-deficient livers. Variable amounts of Cu occurred in this fraction, which is identified in this paper as a metallothionein-like protein. The total amount of Cu and Zn present in fraction 3 has been found to be a function of liver Zn concentration.