Intracellular zinc detector

Zinc plays both physiological and pathological roles in biology, and its concentration in eukaryotic cells is estimated to be as high as 200 µM. Because most of this zinc remains tightly bound to proteins, chemists have long wondered exactly how much "free" or exchangeable zinc is actually available. Now, a team led by Richard B. Thompson of the University of Maryland School of Medicine and Carol Fierke of the University of Michigan, Ann Arbor, has developed a sensor to directly image and quantify zinc in resting mammalian cells (ACS Chem. Biol. 2006, 1, 103). They use their sensor to estimate that the rat tumor and hamster ovary cells they tested are approximately 5 pM in free zinc. This value is significantly higher than the femtomolar concentrations proposed for bacterial cells. The zinc biosensor is based on fluorescence resonance energy transfer from a zinc-bound aryl sulfonamide to a fluorophore tethered to a cell-permeable version of carbonic anhydrase, an enzyme that's highly selective for and sensitive to zinc.