Zinc

Zinc was recognized as an essential trace metal for humans in the early 1960s. Zinc metal existing as Zn2+ is a strong electron acceptor in biological systems without risk of causing oxidant damage to cells. Zn2+ functions in the structure of proteins and is a catalytic component of >300 different enzymes, encompassing almost every aspect of biology, including growth, immune defense, cognitive function, and bone health. Because zinc plays such a fundamental role in the survival of organisms, its concentration in the body must be adequate and well controlled. Zinc homeostasis is maintained by 2 families of zinc transporters, SLC30A [zinc transporter (ZNTs)] and SLC39A [Zrt-, Irt-like proteins (ZIPs)], as well as metallothioneins. In humans, the SLC30A family includes 10 members that transport zinc ions across cell membranes into the extracellular space or move zinc ions across organelle membranes from the cytosol into the organelle. The SLC39A family has 14 members that function in an opposite direction of the SLC30A proteins. Metallothioneins are small cysteine-rich metalloproteins that tightly bind to both essential minerals like zinc and to heavy metal ions, protecting cells from metal toxicity. These proteins work together in concert to balance dietary zinc uptake and endogenous zinc excretion, maintaining cellular zinc concentrations within a narrow physiological range.