Biochemical examples carbonic anhydrase

Substitution of foreign metals for the metals in metalloenzymes (those that contain metals as part of their structures) is an important mode of toxic action by metals. A common mechanism for cadmium toxicity is the substitution of this metal for zinc, a metal that is present in many metalloenzymes. This substitution occurs readily because of the chemical similarities between the two metals (for example, Cd2+ and Zn2+ behave alike in solution). Despite their chemical similarities, however, cadmium does not fulfill the biochemical function of zinc and a toxic effect results. Some enzymes that are affected adversely by the substitution of cadmium for zinc are adenosine triphosphate, alcohol dehydrogenase, and carbonic anhydrase. 

As catalysts, enzymes lower the activation energy for a chemical reaction (see Figure 16.12). Less energy is required to convert reactant molecules to products, which increases the rate of a biochemical reaction compared to the rate of the uncatalyzed reaction. For example, an enzyme in the blood called carbonic anhydrase catalyzes the rapid reaction of carbon dioxide and water to bicarbonate and H+. hi one second, one molecule of carbonic anhydrase catalyzes the reaction of about one miUion molecules of carbon dioxide. 

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