Fumarase C is an enzyme from E. coli (EFumC) that catalyzes the hydration/dehydration reaction between L-malate and fumarate. It catalyzes the hydration of the double bond to form malate. The hydration reaction continues through a carbanion transition state. It has no known metal ion requirement and has a high degree of homology with eukaryotic enzymes. Its homology with cytosolic and mitochondrial enzymes in eukaryotic cells makes it ideal for research. Through x-ray crystallography it has been shown that the enzyme is comprised of a unusual subunit arrangement composed of a core of 20 α-helices, 5 in each of the subunits (shown here is ), and it is a tetrameric enzyme with each monomer containing approximately 460 residues.
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The Debated Fumarase C Active Site
The overall catalytic mechanism of Fumarase drives fumarate formation from L-malate. A water molecule is removed from L-malate to generate fumarate. The first step of this is through a proton removal, and followed by OH- ion removal. The debate for the active site of fumarase involves two active sites that both contain carboxylic acid binding sites; the A and B site. Biochemical data suggests that the Histidine side chain is one of the bases participating in the catalytic reaction [1] In order to determine which is the actual active site of fumarase, Weaver [1] mutated the Histidine side chain, and created two fumarase mutants H129N and H188N. The represents mutation of a residue within site A, and H129N represents a mutated residue in site B. These mutants were developed to hinder the catalytic activity of fumarase. Data was gathered from crystal structure analyses, and activity measurements to confirm the active site [1]. Through a nickel agarose column he purified the histidine tagged proteins[1]. Subsequently, he calculated the specific activities of the wild-type fumarase and the histidine mutants H129N and H188N. Weaver observed that the H188N mutation drastically affected the catalytic reaction, showing an avg activity of 9.62 μ/mL as opposed to the wild type with 4920.0 μ/mL and the H129N mutant with 2080 μ/mL [1].Supporting his hypothesis that site A was the active site, by changing H188 residue they dramatically affected the catalytic activity of the enzyme [1]. Additionally,
Actual Active Site of Fumarase
