title: Development of an LC-MS based enzyme activity assay for MurC: application to evaluation of inhibitors and kinetic analysis.
abstract: An enzyme activity assay, based on mass spectrometric (MS) detection of specific reaction product following HPLC separation, has been developed to evaluate pharmaceutical hits identified from primary high throughput screening (HTS) against target enzyme Escherichia coli UDP-N-acetyl-muramyl-L-alanine ligase (MurC), an essential enzyme in the bacterial peptidoglycan biosynthetic pathway, and to study the kinetics of the enzyme. A comparative analysis of this new liquid chromatographic-MS (LC-MS) based assay with a conventional spectrophotometric Malachite Green (MG) assay, which detects phosphate produced in the reaction, was performed. The results demonstrated that the LC-MS assay, which determines specific ligase activity of MurC, offers several advantages including a lower background (0.2% versus 26%), higher sensitivity (> or = 10 fold), lower limit of quantitation (LOQ) (0.02 microM versus 1 microM) and wider linear dynamic range (> or = 4 fold) than the MG assay. Good precision for the LC-MS assay was demonstrated by the low intraday and interday coefficient of variation (CV) values (3 and 6%, respectively). The LC-MS assay, free of the artifacts often seen in the Malachite Green assay, offers a valuable secondary assay for hit evaluation in which the false positives from the primary high throughput screening can be eliminated. In addition, the applicability of this assay to the study of enzyme kinetics has also been demonstrated.
authors.affiliation: Infection Discovery, Department of Biochemistry, AstraZeneca R&D Boston, 35 Gatehouse Drive, Waltham, MA 02451, USA. gejing.deng@astrazeneca.com
authors.forename: Gejing
authors.initials: G
authors.lastname: Deng
authors.forename: Rong-Fang
authors.initials: RF
authors.lastname: Gu
authors.forename: Stephen
authors.initials: S
authors.lastname: Marmor
authors.forename: Stewart L
authors.initials: SL
authors.lastname: Fisher
authors.forename: Haris
authors.initials: H
authors.lastname: Jahic
authors.forename: Gautam
authors.initials: G
authors.lastname: Sanyal
mesh_terms: D002853:Chromatography, Liquid / Q000379:methods; D004305:Dose-Response Relationship, Drug; D004353:Drug Evaluation, Preclinical / Q000379:methods; D004789:Enzyme Activation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D029968:Escherichia coli Proteins / Q000037:antagonists & inhibitors* / Q000378:metabolism*; D007700:Kinetics; D013058:Mass Spectrometry / Q000379:methods; D010453:Peptide Synthases / Q000037:antagonists & inhibitors* / Q000378:metabolism*; D012680:Sensitivity and Specificity; D013379:Substrate Specificity
chemical_list: D004791:Enzyme Inhibitors; D029968:Escherichia coli Proteins; D010453:Peptide Synthases; C023229:UDP-N-acetylmuramoyl-alanine synthetase