Effect of dietary zinc deficiency on protein synthesis in cell-free systems isolated from rat liver

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.