Intracellular free zinc and zinc buffering in human red blood cells
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Zn2+ has been allowed to equilibrate across the red cell membrane using two agents that increase membrane permeability to this ion: the ionophore A23187 and the specific carrier ethylmaltol. Extracellular free Zn2+ was controlled with EGTA (1,2-di(2-aminoethoxy)ethane-NNN′N′tetra-acetic acid)) buffers, except in the case of ethylmaltol, which itself acts as a buffer. Measurement of cellular zinc content at different levels of free Zn2+ facilitated the study of intracellular Zn2+ binding. It was also possible to estimate intracellular free Zn2+ concentration in untreated cells using a “null-point” technique. Intracellular zinc was found to consist of an inexchangeable component of about 129 μmol/1013 cells and an exchangeable component of 6.7±1.5 μmol/1013 cells, with a free concentration of about 2.4×10−11m. The main component of Zn2+ buffering is hemoglobin, with a dissociation constant of about 2×10−8m.
Key Wordszinc erythrocytes
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