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Effects of Zinc on Mucosal Copper Binding and on the Kinetics of Copper Absorption^1,2,

Peter W. F. Fischer^*, Alex Giroux^* and Mary R. L'Abbe^3,*,,

^* Nutrition Research Division, Bureau of Nutritional Sciences, Food Directorate, Health and Welfare Canada, Ottawa, Ontario K1A 0L2 Canada Department of Animal Science, MacDonald Campus of McGill University, Ste. Anne de Bellevue, Quebec H9X 1C0 Canada

The kinetics of serosal copper transfer and the distribution of copper between metallothionein (MT) and a high-molecular-weight protein fraction (HMWPF) within the mucosal cells were examined, using isolated duodenal segments from rats fed different amounts of zinc. No difference in the V_max or K_on for serosal transfer could be detected between the different zinc groups, suggesting that zinc did not affect this aspect of copper absorption. When intestinal segments from rats fed the low zinc diet were incubated in high copper media, the majority of the copper was associated with the HMWPF, while those from rats fed the high zinc diet had the largest proportion bound to MT. All the intestines incubated in the low copper media, regardless of rat zinc status, had the majority of copper associated with MT. These results suggested that with the low zinc diet, the limited amount of MT present was saturated, and the excess copper was bound to the HMWPF. With larger intakes of zinc, MT synthesis was induced, and the larger amount of this protein was not as readily saturated, resulting in less copper binding to the HMWPF and more to MT. It is suggested that zinc interferes with copper absorption by inducing MT, which sequesters copper in the mucosal cells, making it unavailable for serosal transfer. The copper bound to the HMWPF is available for transfer.

KEY WORDS: • copper • zinc • interactions • metallothionein • absorption

¹ Publication No. 146 of the Bureau of Nutritional Sciences.

² A portion of these results was previously presented at the 66th Annual Meeting of the Federation of American Societies for Experimental Biology, New Orleans, April 15–23, 1962, Fischer, Giroux and L'Abbe (1982) Fed. Proc. 41, 784 (abs. 2998).

³ This work was carried out in partial fulfillment of the requirements for the M.Sc. degree from McGill University.

Manuscript received 2 August 1982.