Fumarase 2: Difference between revisions

The active site (A-site) of the fumarase enzyme is formed by residues from three of the enzyme’s four subunits (shown in <scene name='44/446278/Active_site_chains/3'>different colors</scene>) and is located in a relatively deep pit that is removed from bulk solvent <ref>PMID: 7552727</ref>. The residues that form the <scene name='44/446278/Active_site_residues/3'>active site</scene> include N141b, T100b, S98b, E331c, K324c, N326c, His 188c, (the letter indicates the chain) and a water molecule. It is speculated that the <scene name='44/446278/His_188_active_site/2'>H188</scene> is the most important active site residue, activating the water through a <scene name='44/446278/Short_h_bond/2'>short hydrogen bond</scene>, which increases the basicity of the water molecule. This electron-withdrawing hydrogen bond allows the water molecule to remove the C3 proton of malate, though this model has <scene name='44/446278/Citrate/2'>citrate</scene> in the active site. Complex hydrogen bonding patterns in the active site also help stabilize the aci-carboxylate intermediate<ref name= "Weaver">PMID:9098893</ref>. By increasing the stabilization if the intermediate, the fumarase enzyme can effectively catalyze the hydration/dehydration reaction between L-malate and fumarate.