title: Steady-state kinetic analysis of human ubiquitin-activating enzyme (E1) using a fluorescently labeled ubiquitin substrate.
abstract: We report the synthesis of fluorescently labeled ubiquitin (Ub) and its use for following ubiquitin transfer to various proteins. Using Oregon green (Og) succinimidyl ester, we prepared a population of Ub mainly labeled by a single Og molecule; greater than 95% of the Og label is associated with Lys 6 of Ub. We demonstrate that Og-Ub is efficiently accepted by Ub-utilizing enzymes, such as the human ubiquitin-activating enzyme (E1). We used this fluorescent substrate to follow the steady-state kinetics of human E1-catalyzed Ub-transfer to the ubiquitin-carrier enzyme Ubc4. In this reaction, E1 uses three substrates: ATP, Ubc4, and Ub. The steady-state kinetics of Og-Ub utilization by E1 is presented. We have also used analytical ultracentrifugation methods to establish that E1 is monomeric under our assay condition (low salt) as well as under physiological condition (150 mM NaCl).
authors.affiliation: Chemical Enzymology, DuPont Pharmaceuticals Company, Wilmington, Delaware 19880-0400, USA.
authors.forename: K E
authors.initials: KE
authors.lastname: Wee
authors.forename: Z
authors.initials: Z
authors.lastname: Lai
authors.forename: K R
authors.initials: KR
authors.lastname: Auger
authors.forename: J
authors.initials: J
authors.lastname: Ma
authors.forename: K Y
authors.initials: KY
authors.lastname: Horiuchi
authors.forename: R L
authors.initials: RL
authors.lastname: Dowling
authors.forename: C S
authors.initials: CS
authors.lastname: Dougherty
authors.forename: J I
authors.initials: JI
authors.lastname: Corman
authors.forename: R
authors.initials: R
authors.lastname: Wynn
authors.forename: R A
authors.initials: RA
authors.lastname: Copeland
mesh_terms: D001667:Binding, Competitive; D005452:Fluoresceins / Q000737:chemistry; D006801:Humans; D007700:Kinetics; D008025:Ligases / Q000737:chemistry / Q000378:metabolism*; D008958:Models, Molecular; D020836:Protein Structure, Quaternary; D013379:Substrate Specificity; D044764:Ubiquitin-Activating Enzymes; D044767:Ubiquitin-Protein Ligases; D014452:Ubiquitins / Q000378:metabolism*; D014461:Ultracentrifugation
chemical_list: D005452:Fluoresceins; D014452:Ubiquitins; C401939:oregon green 514; D044767:Ubiquitin-Protein Ligases; D008025:Ligases; D044764:Ubiquitin-Activating Enzymes