4.2.99.20	native enzyme to 2.75 A resolution, together with the structures of the active site mutant proteins Tyr85Phe and Arg124Ala, both at 2.5 A resolution. The enzyme has the predicted alpha/beta hydrolase fold with its core alpha/beta domain capped by a helical lid. The active site, a long groove beneath the cap, contains a number of conserved basic residues and is found to bind exogeneous anions, modeled as sulfate and chloride, in all three crystal structures. The bound anions may mark the binding sites for anionic groups on the substrate	
4.2.99.20	to 1.45 A resolution. The nucleophilicity of the catalytic serine-histidine-aspartate triad is shielded and its catalytic role is limited to being a specific general base by an open-closed conformational change	
4.2.99.20	to 2 A resolution. The overall basic active site displays pronounced hydrophobic character on one side and these properties complement those of the substrate. A complex network of hydrogen bonds involving well-ordered water molecules serves to position key residues participating in the recognition of substrate and subsequent catalysis. Proton shuttle mechanism, reliant on a catalytic triad consisting of Ser89, Asp216 and His243. The reaction is initiated by proton abstraction from the substrate by an activated Ser89. The propensity to form a conjugated system provides the driving force for pyruvate elimination. During the elimination, a methylene group is converted to a methyl and probybly His243 provides a proton, previously acquired from Ser89 for reduction. A conformational change of the protonated His243 may be encouraged by the presence of an anionic intermediate in the active site