Zinc , equilibrium binding studies

The change in conformation seen here (both in the crystal and in solution) may not be due to the zinc so much as to the anion. The X-ray study showed that the change in zinc coordination took place with uptake of an anion in a very hydrophobic pocket. This is consistent with the binding strength order observed SCbT > I" > CD > SO4". In the solution studies two thiocyanate anions are required for the overall change. Apart from the dependence on cation and anion concentration, the equilibrium position between the conformations in solution is temperature and pH dependent. 

The apparent binding constant of copper to the apoprotein were investigated with equilibrium dialysis Four different constants are found. They are pH-dependent. At low pH, two protons compete with copper in the native binding sites. This is not seen at pH 7.0 and above. At alkaline pH-values (pH 10.0) the binding constants are nearly similar. Simultaneous addition of equimolar copper and zinc at pH 5.0 to the apo enzyme results in the formation of an electrophoretically distinct metal-deficient protein species and in the incorporation of copper and zinc in a one-to-one ratio at various concentrations of added metal ions At low ratios of added equimolar metals, not all of the metal ions expected are bound. This may account for the low yields often obtained in reconstitution studies. 

For the binding in organic solvents, zinc porphyrins are used in a number of studies, where a 1 1 complex is predominantly formed and a single equilibrium can describe the host-guest system. 

We propose that the catalysis of Zinc(II) carbonic anhydrase proceeds through a variety of four- and five-coordinate Zinc(II) species in rapid equilibrium. The extensive and stimulating series of spectral studies recently undertaken by Bertini and colleagues (30-32) has strongly suggested to us that the expansion of the coordination sphere of metal-substituted carbonic anhydrase is an important mode of accommodation of anions in the enzyme active site. X-ray evidence(23) and Cl NMR data(34) as well as other spectral studies, have localized the binding of simple anionic inhibitors to the inner coordination sphere of the zinc atom in the acidic form of carbonic anhydrase. 

Zinc. C NMR spectroscopy has been used to examine the equilibrium between Bu OK, 18-crown-6, [Bu2Zn] and [(Bu2Zn)20Bu ] . Stability constants of Zn complexes of 3,6,9,17,20,23-hexaazatricyclo[23.3.1.1(11,15)] triaconta-l(29),ll(30),12,14,25,27-hexaene with maleate, pyrophosphate and norleucine anions have been determined by H NMR spectroscopy. The binding abilities of a novel zinc cavitand have been investigated by H NMR spectroscopy. " The pH dependence of the C NMR spectrum of [Zn(tren)(OH2)] has been reported. The system D-myo-inositol 1,2,6-tris(phosphate)-spermine-Zn + has been studied by P NMR spectroscopy. ... 

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