Norman J. Oppenheimer

Enzyme Modifications for Nuclear Magnetic Resonance Studies: J.T. Gerig, Fluorine Nuclear Magnetic Resonance of Fluorinated Ligands. D.M. LeMaster, Deuteration in Protein-Proton Magnetic Resonance. D.C. Muchmore, L.P. McIntosh, C.B. Russell, D.E. Anderson, and F.W. Dahlquist, Expression and Nitrogen-15 Labeling of Proteins for Proton and Nitrogen-15 Nuclear Magnetic Resonance. D.W. Hibler, L. Harpold, M. Dell'Acqua, T. Pourmotabbed, J.A. Gerlt, J.A. Wilde, and P.H. Bolton, Isotopic Labeling with Hydrogen-2 and Carbon-13 to Compare Conformations of Proteins and Mutants Generated by Site-Directed Mutagenesis, I. P.A. Kosen, Spin Labeling of Proteins. Protein Structure: K. W*aduthrich, Determination of Three-Dimensional Protein Structures in Solution by Nuclear Magnetic Resonance: An Overview. V.J. Basus, Proton Nuclear Magnetic Resonance Assignments. M. Billeter, Computer-Assisted Resonance Assignments. I.D. Kuntz, J.F. Thomason, and C.M. Oshiro, Distance Geometry. R.M. Scheek, W.F. van Gunsteren, and R. Kaptein, Molecular Dynamics Simulation Techniques for Determination of Molecular Structures from Nuclear Magnetic Resonance Data. R.B. Altman and O. Jardetzky, Heuristic Refinement Method for Determination of Solution Structure of Proteins from Nuclear Magnetic Resonance Data. I. Bertini, L. Banci, and C. Luchinat, Proton Magnetic Resonance of Paramagnetic Metalloproteins. H.J. Vogel, Phosphorus-31 Nuclear Magnetic Resonance of Phosphoproteins. J.A. Wilde, P.H. Bolton, D.W. Hibler, L. Harpold, T. Pourmotabbed, M. Dell'Acqua, and J.A. Gerlt, Isotopic Labeling with Hydrogen-2 and Carbon-13 to Compare Conformations of Proteins and Mutants Generated by Site-Directed Mutagenesis, II. Enzyme Mechanisms: D.G. Gorenstein and C.B. Post, Phosphorus-31 Nuclear Magnetic Resonance of Enzyme Complexes: Bound Ligand Structure, Dynamics, and Environment. C.R. Sanders II and M.-D. Tsai, Ligand*b1Protein Interactions via Nuclear Magnetic Resonance of Quadrupolar Nuclei. P.R. Rosevear and A.S. Mildvan, Ligand Conformations and Ligand*b1Enzyme Interactions as Studied by Nuclear Overhauser Effect. B.D. Nageswara Rao, Determination of Equilibrium Constants of Enzyme-Bound Reactants and Products by Nuclear Magnetic Resonance. J.M. Risley and R.L. Van Etten, Mechanistic Studies Utilizing Oxygen-18 Analyzed by Carbon-13 and Nitrogen-15 Nuclear Magnetic Resonance Spectroscopy. J.J. Villafranca, Positional Isotope Exchange Using Phosphorus-31 Nuclear Magnetic Resonance. J.J. Villafranca, Paramagnetic Probes of Macromolecules. In Vivo Studies of Enzymatic Material: S.M. Cohen, Enzyme Regulation of Metabolic Flux. J.S. Cohen, R.C. Lyon, and P.F. Daly, Monitoring Intracellular Metabolism by Nuclear Magnetic Resonance. Appendix: Computer Programs Related to Nuclear Magnetic Resonance: Availability, Summaries, and Critiques. Each chapter includes references. Author Index. Subject Index.

Silent information regulator 2 (Sir2) enzymes catalyze NAD+-dependent protein/histone deacetylation, where the acetyl group from the lysine epsilon-amino group is transferred to the ADP-ribose moiety of NAD+, producing nicotinamide and the novel metabolite O-acetyl-ADP-ribose. Sir2 proteins have been shown to regulate gene silencing, metabolic enzymes, and life span. Recently, nicotinamide has been implicated as a direct negative regulator of cellular Sir2 function; however, the mechanism of nicotinamide inhibition was not established. Sir2 enzymes are multifunctional in that the deacetylase reaction involves the cleavage of the nicotinamide-ribosyl, cleavage of an amide bond, and transfer of the acetyl group ultimately to the 2'-ribose hydroxyl of ADP-ribose. Here we demonstrate that nicotinamide inhibition is the result of nicotinamide intercepting an ADP-ribosyl-enzyme-acetyl peptide intermediate with regeneration of NAD+ (transglycosidation). The cellular implications are discussed. A variety of 3-substituted pyridines was found to be substrates for enzyme-catalyzed transglycosidation. A Brönsted plot of the data yielded a slope of +0.98, consistent with the development of a nearly full positive charge in the transition state, and with basicity of the attacking nucleophile as a strong predictor of reactivity. NAD+ analogues including beta-2'-deoxy-2'-fluororibo-NAD+ and a His-to-Ala mutant were used to probe the mechanism of nicotinamide-ribosyl cleavage and acetyl group transfer. We demonstrate that nicotinamide-ribosyl cleavage is distinct from acetyl group transfer to the 2'-OH ribose. The observed enzyme-catalyzed formation of a labile 1'-acetylated-ADP-fluororibose intermediate using beta-2'-deoxy-2'-fluororibo-NAD+ supports a mechanism where, after nicotinamide-ribosyl cleavage, the carbonyl oxygen of acetylated substrate attacks the C-1' ribose to form an initial iminium adduct.

The structure of the unknown modified nucleoside Q, which is present in the first position of the anticodons of Escherichia coli tRNA Tyr, tRNA His, tRNA Asn, tRNA Asp, is proposed to be 7-(4,5-cis-dihydroxy-1-cyclopenten-3-ylaminomethyl)-7-deazaguanosine (1). The structure of Q was deduced by means of its uv absorption, mass spectrometry, proton magnetic resonance spectroscopy, and studies of its chemical reactivity. The structure of Q is unique since it is a derivative of 7-deazaguanosine having cyclopentenediol in the side chain at the C-7 position. This is the first example of purine skeleton modification in a nucleoside from tRNA.