title: Synthesis of spin-labeled 2-azido-ATP: evidence for distinct nucleotide-binding sites in calcium pump protein from sarcoplasmic reticulum.
abstract: A spin-labeled and photoreactive derivative of ATP was synthesized with the spin label attached to the 2'- or 3'-position of the ribose moiety and an azido group to C2 of the adenine ring (SL-2N3-ATP). Irradiation of this compound at 350 nm generates a nitrene, which then reacts with nucleophiles in its vicinty. SL-2N3-ATP, in the presence of Ca2+, was hydrolyzed by the calcium pump protein (Ca2+-ATPase) of fast twitch skeletal muscle sarcoplasmic reticulum. The SL-2N3-ATP-enzyme complex in the absence of Ca2+ exhibited strongly immobilized ESR spectra. ESR spectra obtained after covalent incorporation of SL-2N3-ATP into Ca2+-ATPase and removal of freely tumbling SL-2N3-ATP exhibited motionally constrained species indicative of distinct and possibly adjacent ATP-binding sites. By contrast, with SL-ATP devoid of the azido group or with the corresponding 'non-cleavable' beta, gamma-methylene triphosphate analogue (SL-AMP-PCP), two distinct sites were not as well resolved in the ESR spectra due to spectral overlap with the signal from the freely tumbling fraction even with the enhanced spectral resolution provided by perdeuteration of the spin label. Thus, SL-2N3-ATP may have general application for ESR studies of ATP-dependent proteins under conditions in which non-covalent interactions are too weak for motionally restricted species to be resolved.
authors.affiliation: Fachbereich Chemie, Universität kaiserlautern, FRG.
authors.forename: P
authors.initials: P
authors.lastname: Jakobs
authors.forename: H E
authors.initials: HE
authors.lastname: Sauer
authors.forename: J O
authors.initials: JO
authors.lastname: McIntyre
authors.forename: S
authors.initials: S
authors.lastname: Fleischer
authors.forename: W E
authors.initials: WE
authors.lastname: Trommer
mesh_terms: D000255:Adenosine Triphosphate / Q000031:analogs & derivatives* / Q000032:analysis / Q000138:chemical synthesis; D000345:Affinity Labels; D001386:Azides / Q000032:analysis* / Q000138:chemical synthesis; D001665:Binding Sites; D000252:Calcium-Transporting ATPases / Q000032:analysis*; D004578:Electron Spin Resonance Spectroscopy; D006868:Hydrolysis; D015394:Molecular Structure; D009711:Nucleotides / Q000032:analysis*; D012519:Sarcoplasmic Reticulum / Q000201:enzymology*
chemical_list: D000345:Affinity Labels; D001386:Azides; D009711:Nucleotides; C042231:2-azidoadenosine 5'-triphosphate; D000255:Adenosine Triphosphate; D000252:Calcium-Transporting ATPases