Structure of native enzyme

Enzyme is a kind of highly efficient and specific biological catalyst. All biochemical reactions in vivo are enzyme-catalyzed reactions. High efficiency and high selectivity of enzyme originated from the hydrophobic interaction between enzyme and substrate and the adjacent effect of catalyzed groups [9]. 

Generally, enzymes with high activity are spherical proteins, of which multipeptide chains are folded widely thus a dense structure is formed. Hydrophilic group of amino acids are distributed mostly outside the surface, but the hydrophobic ones are hidden within the inner space of the structure [10]. 

Different enzymes have active sites constituted of different groups and various conformations. For simple enzyme (the composed imit of enzyme is only amino acid), the active site consists of a few near amino acid residue or side chain groups in these residues in the stereoscopic structure of enzyme molecules. They could be far from each other in the first structure and even in different peptide chains, but they are close to each other within the spacial conformation [7]. 

Generally, there is one active site of enzyme molecule, but there might be a few active sites of some enzymes composed of many sub-units. Generally, one catalyzed 

In the enzyme with a known structure, active site usually locates in the crack and crevice structure of the enzyme. The hydrophobic structure of crack and crevice is in favor of the combination between enzyme and substrate and excludes the entrance of water molecules. But when water molecules also participate in the reaction, crack and crevice need necessary radical residues to construct the required imusual environment for the catalytic reaction. 

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In this chapter, some representative dioxygenases, which have been extensively studied recently, are described from the viewpoints of catalytic activity, structures of native enzymes and intermediates, and reaction mechanisms. 

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