*Geek Box: Mechanisms of Zinc Homeostasis
Zinc homeostasis is controlled by several factors: zinc transporters [ZTs], zinc importers [ZIPs], and metallothionein’s [MTs], which are zinc-sensing molecules in the cell that regulate intracellular zinc levels. Zinc is absorbed by ZIPs in the small intestine, and zinc levels are based on physiological need and regulated at the level of absorption. For example, when levels of zinc in intestinal cells is high, concentrations of free zinc are limited in order to maintain homeostasis.
Intracellular zinc is tightly regulated to prevent the adverse effects of either zinc deficiency or zinc excess. The expression of ZTs, ZIPs, and MTs, is regulated by zinc levels, and has been shown to be tissue specific, i.e., different responses to zinc levels in different tissues.
When free zinc levels in the cell become elevated, MTs bind to that free zinc in order to maintain free zinc concentrations within tight ranges. Zinc levels in the cell are also maintained by a process of transferring zinc within the cell [i.e., from the cytosol to organelles], or exporting zinc out of the cell. All of these mechanisms are designed to respond to fluctuations in free zinc levels within the cell, and maintain zinc homeostasis.