Hepatic copper–and zinc-binding proteins in ruminants

Abstract

1. A study has been made by gel-filtration techniques of the soluble copper- and zinc-binding proteins in livers from calves and sheep of widely differing Cu and Zn status.2. Cu and Zn generally occurred together in three main fractions, with approximate molecular weights of > 75000, 35000 and 12000, and Zn also in one other fraction with molecular weight about 65000. The distribution of the metals between these fractions was variable and dependent on both the Cu and Zn status of the animals.3. Zn was usually absent from the low-molecular-weight fraction in Zn-deficient or high-Cu livers, with Cu also being absent in the former instance.4. The fraction with molecular weight of 35000 was tentatively identified as hepatocuprein. It generally accounted for only 4% of the total hepatic Cu except in Cu-deficient livers.5. The possible relationship of these findings to the mutual antagonism between Cu and Zn is discussed.

The relationship between the zinc status of pigs and the occurrence of copper- and Zn-binding proteins in liver

“…There was no correlation similar to that found in ruminant livers (Bremner & Marshall, 1974b) between the total amount of Cu and Zn in fraction 3 and the liver Zn content. Instead, with one exception, the concentration of Cu in fraction 3 was a function merely of the liver Cu concentration in the pigs given the Zn-supplemented diet ( Fig.…”

“…However, only small differences in plasma Cu concentration were noted in the pigs, although increases in the Cu contents of liver and heart of Zn-deficient rats have been reported (Murthy, Klevay & Petering, 1974). It seems more likely that the protein is involved in the storage and perhaps detoxication of Cu, especially as Cubinding to the protein is often limited in the livers of sheep and calves (Bremner & Marshall, 1974b), which are extremely susceptible to Cu poisoning. It might be expected that Zn-deficient pigs may also have a decreased tolerance of Cu: it is significant, therefore, that pigs given high-Cu diets can suffer a conditioned Zn deficiency and that dietary Zn supplementation in these animals decreases the incidence and severity of Cu toxicosis (Suttle & Mills, 1966a, 6).…”

On the reactivity of metallothioneins with 5,5′-dithiobis-(2-nitrobenzoic acid)

“…The thiol/metal ratio approaches 1 as the copper content increases, in agreement with previous studies indicating a thiol: copper ratio of 1 (Rupp & Weser, 1974). What is unusual here, and was also seen in the native rat liver protein, is that the copper-thionein is stable at least for a period of hours under aerobic conditions after removal from mercaptoethanol by Sephadex G-75 chromatography (Minkel et al, 1980 (Rupp & Weser, 1974;Bremner & Marshall, 1974;Bremner & Young, 1976).…”

Studies on the appearance of a hepatic copper-binding protein in normal and zinc-deficient rats

“…I . Three main fractions, 1-3, were collected as described previously (Bremner & Davies, 1975), with approximate molecular weights of > 65000, 35000 and 12000, as estimated from their elution volumes from the column. The most obvious effect of Cu injection was to increase the amount of Cu, and to a lesser extent of Zn, present in fraction 3 and of Cu in fraction I .…”