Impairment of Cystine-35S Incorporation into Skin Protein by Zinc-deficient Rats

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Abstract
Studies were carried out in young rats to determine the effect of zinc deficiency on the distribution of 35S and incorporation of L-cystine-35S into skin protein. Results indicate that urinary excretion of 35S in zinc-deficient rats was significantly greater than in the zinc-supplemented rats. Conversely, the uptake of 35S in the skin and hair of zinc-deficient rats was considerably lower than control rats. Zinc deficiency drastically reduced the amount of cystine-35S incorporation into skin protein at 4, 8, 16 and 24 hours postinjection. This defect was not due to food intake and can be corrected upon zinc repletion. No significant differences were observed in the protein radioactivity of the liver, kidney, testes and muscles between the two groups. However, a significant increase of cystine-35S was incorporated into pancreas protein in zinc-deficient rats. Additional experiments revealed that zinc-deficient rats had a reduced capacity to utilize L-proline-U-14C and glycine-1-14C for the formation of skin protein as compared to zinc-supplemented rats. These observations strongly suggest that zinc is essential in the synthesis of skin keratin and collagen.