title: Two biochemically distinct classes of fumarase in Escherichia coli.
abstract: Biochemical studies with strains of Escherichia coli that are amplified for the products of the three fumarase genes, fumA (FUMA), fumB (FUMB) and fumC (FUMC), have shown that there are two distinct classes of fumarase. The Class I enzymes include FUMA, FUMB, and the immunologically related fumarase of Euglena gracilis. These are characteristically thermolabile dimeric enzymes containing identical subunits of Mr 60,000. FUMA and FUMB are differentially regulated enzymes that function in the citric acid cycle (FUMA) or to provide fumarate as an anaerobic electron acceptor (FUMB), and their affinities for fumarate and L-malate are consistent with these roles. The Class II enzymes include FUMC, and the fumarases of Bacillus subtilis, Saccharomyces cerevisiae and mammalian sources. They are thermostable tetrameric enzymes containing identical subunits Mr 48,000-50,000. The Class II fumarases share a high degree of sequence identity with each other (approx. 60%) and with aspartase (approx. 38%) and argininosuccinase (approx. 15%), and it would appear that these are all members of a family of structurally related enzymes. It is also suggested that the Class I enzymes may belong to a wider family of iron-dependent carboxylic acid hydro-lyases that includes maleate dehydratase and aconitase. Apart from one region containing a Gly-Ser-X-X-Met-X-X-Lys-X-Asn consensus sequence, no significant homology was detected between the Class I and Class II fumarases.
authors.affiliation: Department of Microbiology, University of Sheffield, U.K.
authors.forename: S A
authors.initials: SA
authors.lastname: Woods
authors.forename: S D
authors.initials: SD
authors.lastname: Schwartzbach
authors.forename: J R
authors.initials: JR
authors.lastname: Guest
mesh_terms: D000595:Amino Acid Sequence; D001426:Bacterial Proteins / Q000145:classification* / Q000235:genetics / Q000276:immunology / Q000502:physiology; D004926:Escherichia coli / Q000201:enzymology* / Q000235:genetics; D005649:Fumarate Hydratase / Q000145:classification* / Q000235:genetics / Q000276:immunology / Q000502:physiology; D005798:Genes, Bacterial; D006358:Hot Temperature; D008969:Molecular Sequence Data; D010957:Plasmids; D011994:Recombinant Proteins; D012689:Sequence Homology, Nucleic Acid; D013379:Substrate Specificity
chemical_list: D001426:Bacterial Proteins; D011994:Recombinant Proteins; D005649:Fumarate Hydratase