A Zinc II Enzyme Carbonic Anhydrase

Zinc is the second most abundant metal, after iron, in humans. There are a number of enzyme systems in which Zn(II) is bound to a peptide (apoenzyme) and is at the active site in the enzyme. Examples of these 

The carbonic anhydrase enzymes catalyze the hydration of COj, shown by the following reaction  

They also catalyze the hydrolysis of organic esters and the hydration of aldehydes, but with such low efficiency that this does not seem to be a significant biological function. Various aspects are discussed in the general references on Zn enzymes noted above and in several more specific reviews and compilations.  

The lack of simple spectroscopic handles for the CA systems has made kinetic studies somewhat difficult. In one study, the C linebroadening method has been used. The most common technique is the stopped-flow indicator method in which a solution of CO /HCOj is mixed with a solution of buffer, enzyme and indicator. The small pH change caused by formation or loss of due to reaction (8.22) can be monitored spectrophotometrically. More recently, the method of choice has been to use 0-enriched COj/HCOj in combination with a mass 

The problem with the model Zn(II) complexes which led to the prediction that p g 8 has now been resolved and attributed to the fact 

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