ich provides a good model of zinc metabolism in animal cells. They found that when the amount of zinc in the cell increases to a point where zinc is no longer needed for cellular tasks, the extra zinc binds tightly to the protein Zur. This reaction in turn shuts down the zinc intake pump.
In the case of the regulatory protein ZntR, the opposite happens when it combines with zinc. When ZntR senses any extra zinc after the intake pump has been shut off, ZntR binds with the zinc, turning on the export pump. Any unwanted and potentially dangerous zinc is pumped out of the cell.
The researchers determined the concentrations of zinc required within the cell in order for the proteins to turn off and on the pumps. They showed that the regulatory system is so sensitive and finely tuned that zinc does not have the opportunity to float freely in the cells cytoplasm before it binds to either Zur or ZntR, depending on the cycle.
"The zinc concentration is so low in between pump activity that free-floating zinc just doesnt exist," said Outten, now a post-doctoral researcher at Johns Hopkins Bloomberg School of Public Health. "Its a kinetic process any zinc that shows up in the cell is immediately taken away, to work reactions in the cell, to bind to proteins such as Zur or ZntR or, if no zinc is needed, to be sent packing out of the cell."
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