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Biochemical effects of zinc difficiency: changes in activities of zinc-dependent enzymes and ribonucleic acid and deoxyribonucleic acid content of tissues.

Abstract Zinc is known to be essential for the function of several enzymes and its role in polymeric organization of ribonucleic acid (RNA) and deoxyribonucleic acid (DNA) molecules has been postulated; however, conflicting results have been reported concerning changes occuring in activities of zinc-dependent enzymes and content of RNA and DNA in zinc-deficient tissues. Present studies were carried out in young pigs made zinc-deficient by diet. Control pigs were pair-fed and received supplemental zinc (90p.p.m.). Pigs were put to death on the thirtieth day. Zinc content was measured by atomic absorption spectrophotometry. RNA and DNA content was determined with the Schmidt-Thannhauser method. Activities of the following zinc-dependent enzymes were assayed in tissue homogenates under optimal conditions by standard methods and expressed per milligram of DNA: alcohol dehydrogenase (ADH), lactic dehydrogenase (LDH) and aldolase (ALD) in liver; ADH, ALD, and alkaline phosphatase (AP) in kidney, carboxypeptidase (CPD) and LDH in pancreas; and ADH, AP, LDH, and ALD in bone. Succinic dehydrogenase, an iron-dependent enzyme, and isocitric dehydrogenase, a manganese-dependent enzyme, were also assayed in the kidney as controls. Zinc content and RNA/DNA ratios were significantly reduced in the liver, kidney, pancreas, and bone, but DNA per milligram of wet weight remained unaltered in zinc-deficient animals as compared to their pair-fed controls. Only zinc-dependent enzymes revealed significantly reduced activities in zinc-deficient tissues; exceptions were LDH in the liver and pancreas, and ALD in bone. Addition of small amounts of ethylenediaminetetraacetate (EDTA) to tissue homogenates significantly reduced activities of ADH, AP, and CPD, but not the activities of LDH and ALD, thus revealing the differences in affinity for zinc of the various enzymes. These studies provide a basis for understanding the role of zinc in cellular functions.