Microminerals : Zinc

Zn plays important structural and catalytic functions in the body. Zinc fingers are supersecondary structures (motifs) in proteins (for example, transcription factors) that bind to DNA and regulate gene expression (Fig. 1). Hundreds of enzymes require Zn for activity.
Examples include alcohol dehydrogenase, which oxidizes ethanol to acetaldehyde ; carbonic anhydrase, which is important in the bicarbonate buffer system ; porphobilinogen synthase of heme synthesis, which is inhibited by lead (lead replaces the zinc); and the nonmitochondrial isoform of superoxide dismutase (SOD), which also requires Cu . Dietary sources of Zn include meat, fish, eggs, and dairy products. Phytates (phosphate storage molecules in some plant products) irreversibly bind Zn in the intestine, decreasing its absorption, and can result in a deficiency. [Note: Phytates may also bind Ca²⁺ and nonheme Fe.] Several drugs (for example, penicillamine) chelate metals, and their use may cause Zn deficiency. [Note: Severe deficiency is seen with a defect in the intestinal transporter for Zn that results in the malabsorption disorder acrodermatitis enteropathica. Symptoms include rashes, slowed growth and development, diarrhea, and immune deficiencies. Vision problems may also occur because Zn is needed in the metabolism of vitamin A.]

Figure 1:  Zinc (Zn) finger is a common motif in proteins that bind DNA. Cys = cysteine; His = histidine.
Eukaryotic cells infected with bacteria can restrict availability of the essential micronutrients Fe, Mn, and Zn to the pathogens. This decreases the intracellular survival of the pathogen and is known as “nutritional immunity.”