Zinc , equilibrium binding

Many metals are incorporated by equilibrium binding into their specific sites on their apoproteins. The rate of synthesis of the apoprotein by the cells or tissues controls the rate of incorporation. Most zinc and some copper proteins exhibit such behavior. The process of iron incorporation is far more... 

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. 

This enzyme, which catalyzes the hydrolysis of glucosides, is a second example where Zn2+ may only play a structural role. The enzyme always contains Ca2+, which is necessary for catalytic activity, but the enzyme from Bacillus subtilis also contains zinc, which is thought to dimerize two monomeric units. However, there is some doubt over this matter, as the enzyme appears to exist as a monomer-dimer equilibrium in the absence of zinc. Zinc may then bind to the dimer only.532... 

The answer became clear with the realization that the highest rates of carbon dioxide hydration require the presence of buffer, suggesting that the buffer components participate in the reaction. The buffer can bind or release protons. The advantage is that, whereas the concentrations of protons and hydroxide ions are limited to 10 M at neutral pH, the concentration of buffer components can be much higher, on the order of several millimolar. If the buffer component BH+ has a pi T of 7 (matching that for the zinc-bound water), then the equilibrium constant for the reaction in Figure 9 28 is... 

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