Zinquin Ester—a Reagent for the Investigation of the Role of Available ZN(II) in Living Systems

Zn(II) has an important role in biochemical and nutritional processes and about 300 enzymes contain Zn(II) as an essential component. Most of this intracellular Zn(II) is strongly complexed and hence not generally available to the cell. However the cell has small amounts [about 10% of the total cellular Zn(II)] of readily exchangeable [i.e. less strongly bound] Zn(II) which are important in many situations associated with cell activation, cell growth and cell death. Zinquin ester, a reagent we have developed specifically for the measurement of this less strongly bound cellular Zn(II), selectively forms a highly fluorescent complex with zinc(II). It is capable of detecting intracellular Zn(II) down to low nanomolar levels. Estimates of the concentration of intracellular available Zn(II) range from about M in the cytoplasm of many cells to about M in some vesicles. This paper describes some of the ways that Zinquin ester has been used to examine the roles of available Zn(II) in cell processes.