Zinc-containing Biomolecules

Zinc proteins are common, but the absence of any accessible oxidation states apart from Zn(II) means that they cannot act as redox proteins. One of the problems in working with with Zn(II) is that it is, as a d10 system, spectroscopically silent , which limits the type of studies that can be used to probe its chemistry in biomolecules. However, several zinc proteins are relatively low molecular weight species and these were characterized by crystal structure analysis some decades ago. 

A simple representation of the tetrahedral and distorted square pyramidal ligand environments for zinc(II) in carbonic anhydrase II and carboxypeptidase A respectively both feature a coordinated water group. A simplified mechanism for the CO2/HCO3- process catalysed by carbonic anhydrase is also shown, at right. 

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A number of investigations of metal-containing biomolecules are described in this chapter. The elements include aluminium, arsenic, cadmium, copper, gold, lead, platinum and zinc. 

Polysaccharides are used as structural units and as stored energy sources. Proteins are used to construct muscle and enzymes that also contain metals such as zinc, manganese, and iron. There are many other important biomolecules present at lower concentrations such as DNA and RNA, which are also released into the soil solution. All can be the source of smaller molecules in the soil solution. 

There are a number of enzymes that catalyse the dismutation of superoxide in vivo, viz. the superoxide dismutases [50,51], They are metalloproteins which contain copper, zinc, manganese or iron as the prosthetic group. The enzyme catalase exists in vivo to degrade hydrogen peroxide within cells to form water and oxygen [43]. As stated earlier, there are barely detectable amounts of these two enzymes in the synovial fluid of arthritic patients and hence both superoxide radicals and hydrogen peroxide are potential mediators of damage to the biomolecules of the synovial fluid. 

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