title: Electron spin echo envelope modulation studies of pyruvate kinase active-site complexes.
abstract: Electron spin echo envelope modulation (ESEEM) spectroscopy, with Mn2+ and VO2+ as paramagnetic probes, was used to examine active-site structures at the protein-based divalent cation site of rabbit muscle pyruvate kinase in the presence of substrates, products, and the requisite inorganic cofactors. Two different VO.protein complexes were clearly distinguished, which differed with respect to coordination of the active-site lysine to VO2+. Lysine coordination was sensitive to the presence of pyruvate and phosphoenolpyruvate (PEP) and to the nature of the monovalent cation. In the presence of MgATP and oxalate, a 4-MHz 31P contact interaction was observed, which indicates that the ATP is directly coordinated to Mn2+ at the protein-based site. No 31P contact interactions were observed, however, in the presence of PEP. Pyruvate was determined to be a bidentate ligand of VO2+, on the basis of the observation of 2.2- and 5.4-MHz 13C contact interactions between VO2+ and [1-13C]pyruvate and [2-13C]pyruvate, respectively. Magnetic coupling between VO2+ or Mn2+ and 23Na, 39K, and 133Cs was observed, demonstrating the close proximity of the monovalent cation and the protein-based divalent cation.
authors.affiliation: Department of Molecular Pharmacology, Albert Einstein College of Medicine, Bronx, New York 10461.
authors.forename: P A
authors.initials: PA
authors.lastname: Tipton
authors.forename: J
authors.initials: J
authors.lastname: McCracken
authors.forename: J B
authors.initials: JB
authors.lastname: Cornelius
authors.forename: J
authors.initials: J
authors.lastname: Peisach
mesh_terms: D000818:Animals; D001665:Binding Sites; D002412:Cations; D004578:Electron Spin Resonance Spectroscopy; D066298:In Vitro Techniques; D008345:Manganese / Q000378:metabolism; D009132:Muscles / Q000201:enzymology; D011770:Pyruvate Kinase / Q000378:metabolism*; D011817:Rabbits; D014638:Vanadates / Q000378:metabolism
chemical_list: D002412:Cations; D014638:Vanadates; D008345:Manganese; D011770:Pyruvate Kinase