title: Larger increases in sensitivity to paracatalytic inactivation than in catalytic competence during experimental evolution of the second beta-galactosidase of Escherichia coli.
abstract: Second-order rate constants (M-1.s-1) at 25 degrees C and pH 7.5 for inactivation of first-generation (ebga and ebgb), second-generation (ebgab and ebgabcd) and third-generation (ebgabcde) experimental evolvants of the title enzyme by 2',4'-dinitrophenyl 2-deoxy-2-fluoro-beta-D-galactopyranoside are 0.042, 0.30, 10, 24 and 57 respectively. Only partial inactivation is observed, except for ebgabcde. At a single high inactivator concentration, inactivation of the wild-type ebgo is also seen. The changes in sensitivity to the paracatalytic inactivator (over a range of 10(3.3)) are larger than changes in kcat/Km for lactose (over a range of 10(2.7)) or nitrophenyl galactosides (over a range of only 10(1.3)), or changes in degalactosylation rate (over a range of 10(1.7)). These data raise the possibility that evolution in the reverse sense, towards insensitivity to a paracatalytic inactivator with a proportionally lower effect on transformation of substrate, may become a mechanism for the development of bacterial resistance to antibiotics that act by paracatalytic enzyme inactivation.
authors.affiliation: Department of Chemistry (M/C 111), University of Illinois at Chicago, 845 West Taylor Street, Chicago, IL60607-7061, USA.
authors.forename: S V
authors.initials: SV
authors.lastname: Calugaru
authors.forename: S
authors.initials: S
authors.lastname: Krishnan
authors.forename: C J
authors.initials: CJ
authors.lastname: Chany
authors.forename: B G
authors.initials: BG
authors.lastname: Hall
authors.forename: M L
authors.initials: ML
authors.lastname: Sinnott
mesh_terms: D001665:Binding Sites; D004926:Escherichia coli / Q000201:enzymology*; D006863:Hydrogen-Ion Concentration; D007527:Isoenzymes / Q000037:antagonists & inhibitors*; D007700:Kinetics; D015394:Molecular Structure; D009598:Nitrophenylgalactosides / Q000494:pharmacology*; D001616:beta-Galactosidase / Q000037:antagonists & inhibitors*
chemical_list: D007527:Isoenzymes; C074857:2',4'-dinitrophenyl 2-deoxy-2-fluorogalactopyranoside; D009598:Nitrophenylgalactosides; D001616:beta-Galactosidase