<p>A number of enzymes, belonging to the lyase class, for which fumarate is a substrate, have been shown to share a short conserved sequence around amethionine which is probably involved in the catalytic activity of this typeof enzymes [<cite idref="PUB00000586"/>, <cite idref="PUB00001722"/>]. The following are examples of members of this family:</p> <ul><li> <db_xref db="SWISSPROT" dbkey="P32427"/>: 3-carboxymuconate lactonizing enzyme, <db_xref db="EC" dbkey="5.5.1.2"/> (3-carboxy-cis,cis-muconate cycloisomerase), an enzyme involved in aromatic acids catabolism [<cite idref="PUB00000374"/>]. </li><li> <db_xref db="SWISSPROT" dbkey="P24057"/>: Delta-crystallin shares around 90% sequence identity with arginosuccinate lyase, showing that it is an example of a 'hijacked' enzyme - accumulated mutations have, however, rendered the protein enzymatically inactive.</li><li> <db_xref db="SWISSPROT" dbkey="P05042"/>: Class I Fumarase enzyme, <db_xref db="EC" dbkey="4.2.1.2"/> (fumarate hydratase), which catalyses the reversible hydration of fumarate to L-malate. Class I enzymes are thermolabile dimeric enzymes (as for example: <taxon tax_id="562">Escherichia coli</taxon> fumC).</li><li> <db_xref db="SWISSPROT" dbkey="P04424"/>: Arginosuccinase, <db_xref db="EC" dbkey="4.3.2.1"/> (argininosuccinate lyase), which catalyses the formation of arginine and fumarate from argininosuccinate, the last step in the biosynthesis of arginine. </li><li> <db_xref db="SWISSPROT" dbkey="P04422"/>: Aspartate ammonia-lyase, <db_xref db="EC" dbkey="4.3.1.1"/> (aspartase), which catalyses the reversible conversion of aspartate to fumarate and ammonia. This reaction is analogous to that catalyzed by fumarase, except that ammonia rather than water is involved in the trans-elimination reaction. </li><li> <db_xref db="SWISSPROT" dbkey="P00923"/>: class II Fumarase enzyme, <db_xref db="EC" dbkey="4.2.1.2"/>, are thermostable and tetrameric and are found in prokaryotes (as for example: E. coli fumA and fumB) as well as in eukaryotes. The sequence of the two classes of fumarases are not closely related.</li><li> <db_xref db="SWISSPROT" dbkey="P25739"/>: Adenylosuccinase, <db_xref db="EC" dbkey="4.3.2.2"/> (adenylosuccinate lyase) [<cite idref="PUB00004940"/>], which catalyses the eighth step in the de novo biosynthesis of purines, the formation of 5'-phosphoribosyl-5-amino-4-imidazolecarboxamide and fumarate from 1-(5-phosphoribosyl)-4-(N-succino-carboxamide). That enzyme can also catalyse the formation of fumarate and AMP from adenylosuccinate. </li></ul><p>This signature contains the conserved methionine which is probably involved in the catalytic activity.</p> Fumarate lyase, conserved site