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Effect of Dietary Zinc Deficiency on Protein Synthesis in Cell-Free Systems Isolated from Rat Liver¹

U.S. Department of Agriculture Human Nutrition Research Center on Aging, Tufts University, Boston, MA 02111

This study presents evidence for the direct involvement of zinc in the translation of polypeptide chains in rat liver. Cell-free systems consisting of polyribosomes and fractions, enriched with aminoacyl-tRNA synthetase for incorporation of amino acids into trichloroacetic acid-insoluble proteins, were prepared from livers of three populations of rats: 1) rats fed ad libitum a diet containing 25 ppm zinc; 2) rats fed a diet containing less than 1 ppm zinc; and 3) rats pair fed to the zinc-deficient group a diet containing 25 ppm zinc. Group 2 showed typical signs of zinc deficiency, including decreased bone zinc. The protein synthetic ability of systems isolated from zinc-deficient rats was considerably depressed, resulting in incorporation of 59–69% of the amino acids incorporated by systems from pair-fed rats and 54–59% of those incorporated by ad libitum-fed control animals. This effect was significant after only 14 d of the dietary regimen. Experiments performed by mixing polyribosomes and synthetase fractions from the different groups indicated that a defect is located in the synthetase fraction. Acylation of tRNA by the synthetase fraction also was assayed and found to be 69–90% of that in zinc-sufficient preparations. It is suggested that one or more of the aminoacyl-tRNA synthetase enzymes from the rat liver may be zinc dependent.

KEY WORDS: • zinc deficiency • protein synthesis • polyribosomes • rat • liver

¹ Presented in part at the 70th Annual Meeting of the Federation of American Societies for Experimental Biology, April 13–18, 1986, St. Louis, MO. Hicks, S. E. & Wallwork, J. C. (1986) The involvement of zinc in cell-free protein synthesizing systems from rat liver. Fed. Proc. 45: 1083 (abs. 5404).

² On sabbatical from Wellesley College Department of Chemistry, Wellesley, MA.

³ Present address: Division of Human Nutrition, Department of Preventive Medicine and Community Health, University of Texas Medical Branch, Galveston, TX 77550.

Manuscript received 1 October 1986. Revision accepted 3 March 1987.