Fumarase is a tetrameric enzyme that catalyzes the dehydration of L-malate to Fumarate and vice versa. It does so by deprotonating the C3 carbon of L-malate and removing an OH group from the C2 carbon, or by adding a water across the double bond of fumarate.
Fumarase has two sites where substrates can bind. The first site, which is referred to as "site A" in a Weaver et al. 1997 study [1] is deeper in the enzyme structure than the second site, "site B". In addition it is composed of atoms from 3 of the four subunits, where as site B is completely composed of atoms from a single sub unit. [2]
A dilemma arose over which was the active site. A 1996 crystallographic study showed L-malate and beta-trimethylsilyl maleate in site B.[3] However, it was suspected that site A was the active site, because no active monomeric unit of fumerase had ever been described. Furthermore, in the previously mentioned study, citrate, which is a known competitive inhibitor of fumarase activity, was used at high concentration as the crystallizing agent. Hence, this would explain L-malate's association at site B rather than A. In a 1997 study by Weaver et. al, mutations were introduced at each site. Since Histidine was suggested to be one of the bases participating in the catalytic activity of fumarase Sandbox Wabash 03 fumarase. Click above on edit this page to modify. Be careful with the < and > signs.
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