Studies on the Appearance of a Copper-Binding Protein in Rat Liver

Studies on metalloproteins in ruminant livers showed the relationship between the total amount of zinc and copper present in a metallothionein-like fraction (designated fraction 111) and the zinc content of livers can be described by the equation y = 0.74~-0.25 (s.E. of regression coefficient = h0.04, P<O.OOl), where y is the number of g-atoms of Cu+Zn in fraction III/g of fresh liver and x is the number of g-atoms of Zn/g of fresh liver. On the basis of this finding it was suggested that zinc, but not copper, may control either the synthesis or degradation of this protein (Bremner, 1974). Later work indicated a primary role for zinc in the synthesis de nouo of a similar metal-binding component in rat liver (Bremner et al., 1973; Davies et al., 1973). Since copper was invariably present in these proteins, a study has been made of the effects of Cut+ injection on the appearance of this fraction in rat liver. Male rats (150g) were injected intraperitoneally with either lOOpg or 300pg of Cu2+ (as CuS04 in 0.9% NaCI), killed from 0.5 to 8 h later, and their livers removed and processed as described previously (Bremner et al., 1973). Injection of lOOpg of Cut+ (as CuSO,) promoted increases in both the copper and the zinc content in all livers, although large variations were observed between individual animals similarly treated. Liver copper contents ranged from 8.4 to 17.3pg/g of fresh liver and zinc contents from 19.1 to 40.6pglg of fresh liver in the group slaughtered 8h after injection. Regardless of this variation, the incremental increases in copper and zinc contents in each individual liver were about equal. Three copperand zinc-binding fractions (I, I1 and 111) with approximate molecular