Biochemicals, enol-containing

B. Enol-containing Biochemicals and Pharmaceuticals and Their Metal... 

The carbonyl functionality is one of the most abundant functional groups in biomolecules and pharmaceuticals, including many a- and /3-carbonyl derivatives of ketones and aldehydes and their enol tautomers, which upon deprotonation can form entropy-favored 5-membered (37) and 6-membered (38) chelates with metal ions. In this section, the role of metal ions in the action of some enol-containing biochemicals and pharmaceuticals and the structures of their metal complexes are discussed. 

One of the simplest biochemical addition reactions is the hydration of carbon dioxide to form carbonic acid, which is released from the zinc-containing carbonic anhydrase (left, Fig. 13-1) as HC03-. Aconitase (center, Fig. 13-4) is shown here removing a water molecule from isocitrate, an intermediate compound in the citric acid cycle. The H20 that is removed will become bonded to an iron atom of the Fe4S4 cluster at the active site as indicated by the black H20. An enolate anion derived from acetyl-CoA adds to the carbonyl group of oxaloacetate to form citrate in the active site of citrate synthase (right, Fig. 13-9) to initiate the citric acid cycle. 

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