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Zinc Deficiency and Incorporation of ¹⁴C-labeled Methionine into Tissue Proteins in Rats

Biochemistry Research Laboratory, Veterans Administration Hospital, and the Department of Biochemistry, The Johns Hopkins University, Baltimore, Maryland 21218

Studies to determine the role of zinc on the rate of incorporation of ¹⁴C-labeled methionine into tissue proteins were undertaken. The results show that rats fed a semipurified diet deficient in zinc incorporated significantly less DL-methionine-2-¹⁴C into plasma, liver, kidney and muscle at 2 hours postinjection than rats receiving a zinc-supplemented diet. Similar results at 4 and 8 hours were noted in liver and kidney. The same trends were also observed when DL-methionine-1-¹⁴C or L-methionine-methyl-¹⁴C was injected. When unlabeled methionine was injected, all three groups of zinc-deficient rats showed a significant decrease in the specific activities of liver and kidney protein as compared with zinc-supplemented rats. Conversely, the incorporation of all three ¹⁴C-labeled methionines into pancreatic protein at 2 hours was significantly greater in zinc-deficient rats than in zinc-supplemented rats. This enhanced conversion disappeared when zinc-deficient animals were previously injected with nonradioactive methionine. Total radioactivity as well as radioactivity in TCA-soluble fractions of liver and kidney were unaffected by zinc deficiency; therefore, the reduction in protein synthesis was probably unrelated to methionine uptake. It was further demonstrated that the effects on the incorporation of labeled methionine into tissue proteins were due to zinc deficiency per se rather than to reduced food intake.

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