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Copper- and Zinc-binding Proteins in Sheep Liver and Intestine: Effects of Dietary Levels of the Metals^1,2,3,

Department of Poultry Science, The Pennsylvania State University, University Park, PA 16802

Liver cytosol from sheep fed diets containing 2.2, 11.3 or 47 µg Cu/g diet with or without supplemental zinc (543 or 46 µg Zn/g diet), fractionated on Sephadex G-100, yielded three main copper- and zinc-containing proteins with approximate molecular weights of > 150,000, 27,000 and 10,000. Amino acid analysis of the 10,000-molecular-weight proteins were of the metallothionein type. Copper-chelatin was not present in sheep liver cytosol. Copper concentration of the metallothionein fraction increased (P < 0.01) as dietary copper increased from 2.2 to 11.3 µg Cu/g, but did not increase further when dietary copper increased to 47 µg Cu/g in unsupplemented sheep. A low-molecular-weight (approximately 3,500) copper-, but not zinc-containing fraction appeared at this highest level of copper. Zinc supplementation of the diet increased not only the zinc content of the metallothionein fraction but also its copper content, most dramatically in sheep fed the highest copper level. In intestinal mucosal cytosol, no copper and little zinc was associated with the metallothionein fraction which was not affected by dietary treatment. Evidence from this study suggests that sheep have limited capacity to synthesize metallothionein in response to increased dietary copper.

KEY WORDS: • metallothionein • copper • zinc • binding proteins • sheep • liver

¹ Authorized for publication on May 1, 1979 as Paper No. 5726 in the Journal Series of the Pennsylvania Agricultural Experiment Station.

² Supported in part by Fair Funds administered by The Pennsylvania Department of Agriculture.

³ From a thesis submitted by William W. Saylor in partial fulfillment of the requirements for the degree of Doctor of Philosophy.

⁴ Present address: Department of Animal Science and Agricultural Biochemistry. University of Delaware, Newark, DE 19711.

⁵ To whom reprint requests should be sent.

Manuscript received 7 May 1979.