title: Purification and characterization of 4-methylmuconolactone methyl-isomerase, a novel enzyme of the modified 3-oxoadipate pathway in nocardioform actinomycetes.
abstract: The novel enzyme 4-methyl-2-enelactone methyl-isomerase was detected in, and purified to electrophoretic homogeneity from, p-toluate-grown cells of Rhodococcus rhodocrous N75, a nocardioform actinomycete. The enzyme was very thermostable and had a native Mr of 75,500; as the monomer had an Mr of 17,000, the enzyme is probably tetrameric. The new isomerase is highly specific with respect to its lactone substrate, only accepting (+)-(4S)-4-methylmuconolactone (4-carboxymethyl-4-methylbut-2-en-1,4-olide), and the putative isomerization reaction intermediate 1-methylbislactone ((-)-1-methyl-3,7-dioxo-2,6-dioxabicyclo-[3.3.0]octane) as substrates, and yielding (-)-(4S)-3-methylmuconolactone (4-carboxymethyl-3-methylbut-2-en-1,4-olide) as product. Some other lactone analogues acted as competitive inhibitors. Our data suggest that the isomerization does not involve actual methyl migration, but proceeds via the 1-methybislactone.
authors.affiliation: Department of Agricultural and Environmental Science, University of Newcastle upon Tyne, U.K.
authors.forename: N C
authors.initials: NC
authors.lastname: Bruce
authors.forename: R B
authors.initials: RB
authors.lastname: Cain
authors.forename: D H
authors.initials: DH
authors.lastname: Pieper
authors.forename: K H
authors.initials: KH
authors.lastname: Engesser
mesh_terms: D002850:Chromatography, Gel; D002852:Chromatography, Ion Exchange; D004795:Enzyme Stability; D006358:Hot Temperature; D019751:Intramolecular Transferases; D007535:Isomerases / Q000302:isolation & purification* / Q000378:metabolism; D007700:Kinetics; D007783:Lactones / Q000378:metabolism; D008970:Molecular Weight; D012240:Rhodococcus / Q000201:enzymology*
chemical_list: D007783:Lactones; D007535:Isomerases; C061587:4-methylmuconolactone methyl-isomerase; D019751:Intramolecular Transferases