title: Spin-labeled analogues of ATP, ADP and AMP: substitutes for normal nucleotides in biochemical systems.
abstract: The different roles and effectiveness of adenosine monophosphate, diphosphate and triphosphate labeled at the 6 position of the purine ring with 2,2,6,6-tetramethylpiperidine-1-oxyl in reactions catalyzed by Escherichia coli glutamine synthetase (GS) have been investigated. Our results show that the spin-labeled ATP (Tempo-ATP) serves as a substrate in the glutamine synthesis reaction and in the adenylation of E. coli glutamine synthetase catalyzed by ATP: glutamine adenylyl transferase (ATase) with essentially the same effectiveness as normal ATP. In another reaction (gamma-glutamyltransferase), Tempo ADP serves as an effector with a Km of 9.4 . 10(-8) M compared to 1.2 . 10(-8) M for the normal ADP, while covalently bonded Tempo-AMP serves as a modifier on the catalytic properties of E. coli glutamine synthetase just as the covalently bonded normal AMP does. The dissociation constants between the labeled nucleotides, Mn2+, Mg2+ and Ca2+ are in the same order of magnitude as the binding constants for those cations and the corresponding normal nucleotides. Our findings indicate that the spin-labeled nucleotides are good substitutes for the normal nucleotides in the biochemical systems studied.
authors.affiliation: Department of Biochemistry, Faculty of Medical Sciences, University of Jos, Plateau State, Nigeria.
authors.forename: G A
authors.initials: GA
authors.lastname: Ubom
authors.forename: J B
authors.initials: JB
authors.lastname: Hunt
authors.forename: R B
authors.initials: RB
authors.lastname: Timmons
mesh_terms: D000244:Adenosine Diphosphate / Q000031:analogs & derivatives; D000255:Adenosine Triphosphate / Q000031:analogs & derivatives; D002413:Cations, Divalent / Q000378:metabolism; D003497:Cyclic N-Oxides; D004578:Electron Spin Resonance Spectroscopy; D004926:Escherichia coli / Q000201:enzymology; D005974:Glutamate-Ammonia Ligase / Q000378:metabolism*; D008956:Models, Chemical; D013050:Spectrometry, Fluorescence; D013113:Spin Labels; D013379:Substrate Specificity
chemical_list: D002413:Cations, Divalent; D003497:Cyclic N-Oxides; D013113:Spin Labels; C060597:6-(2,2,6,6-tetramethylpiperidine-1-oxyl)-adenosine triphosphate; C060599:6-(2,2,6,6--tetramethylpiperidine-1-oxyl)-adenosine monophosphate; C060598:6-(2,2,6,6,-tetramethylpiperidine-1-oxyl)-adenosine diphosphate; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D005974:Glutamate-Ammonia Ligase