= Fumarase C
{c}
\b[Fumarase C], often designated FumC, is a classII form of <fumarate hydratase>. It catalyzes reversible hydration of <fumarate> to <L-malate>. The protein designation should be tied to an organism: <Escherichia coli fumarase C> is a well-studied species-specific example, while the broader enzyme-activity name does not specify one protein sequence.<Crystallographic studies of the catalytic and a second site in fumarase C from Escherichia coli by T. M. Weaver and others>[Abstract: reaction and classII fumarase superfamily]{ref}
The net substrate inventory makes the chemistry explicit:
$$
\mathrm{C_4H_2O_4^{2-}+H_2O\rightleftharpoons C_4H_4O_5^{2-}}.
$$
Four carbon atoms remain four; adding water changes hydrogen and oxygen content without changing the total charge. This hydration is chemically distinct from oxidation of <L-malate> to <oxaloacetate>. The enzyme accelerates a reversible reaction rather than making its net direction independent of conditions.<Fumarate hydratase in IUBMB Enzyme Nomenclature>[EC4.2.1.2, accepted reversible reaction]{ref}
The1995 <X-ray crystallography> study of the E.coli enzyme resolved an assembly of four identical <protein subunits> at2.0Å. Its proposed <active site> involved contributions from three of the four <protein subunits>; a local catalytic environment therefore need not lie inside just one polypeptide chain. A1996 follow-up with bound compounds distinguished the catalytic A-site from a nearby second binding site. These experiments also show why observing ligand binding does not by itself identify a catalytic site.<The multisubunit active site of fumarase C from Escherichia coli by T. M. Weaver and others>[Abstract: tetramer and multisubunit active site]{ref}<Crystallographic studies of the catalytic and a second site in fumarase C from Escherichia coli by T. M. Weaver and others>[Abstract: catalytic siteA versus second siteB]{ref}
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