Nuclear magnetic resonance (NMR) and other spectroscopic studies are planned to probe the structure and reactivity of proteins (peroxidases, cytochrome P450, heme oxygenase) and model metal tetrapyrrole complexes involved in the metabolism and activation of dioxygen, hydroperoxides, and related small molecules. The paramagnetic nature of most of the active forms of these proteins and their synthetic models """"""""lights up"""""""" the active site with an expanded scale of hyperfine shifts that enhances resolution, allows complex, multicomponent reacting systems to be analyzed, and provides unique information on the magnetic properties and electronic structure of these chromophores. Promising preliminary advances in the application of multi-pulse 2D NMR methodology to paramagnetic tetrapyrrole complexes and proteins will be thoroughly developed for resonance assignment and electronic/magnetic/molecular structure determination on both models and proteins. Emphasis will be given to problems posed by paramagnetic enzymes that are considered large by conventional NMR standards. These techniques will be employed to characterize the identity, disposition, and protonation state of key residues within the heme pocket, the catalytically relevant hydrogen-bonding networks, and the sites of substrate binding in a variety of plant, fungal, and mammalian heme peroxidases. They will also be used to probe the influence of substrate binding on the structure and dynamic properties of these active sites. The scope and limitations of the 2D methodology for bacterial heme mono- oxygenases will also be explored. Skeletally modified porphyrins (chlorins, isobacteriochlorins, substituted) are important as prosthetic groups in some proteins (nitrate, sulfate reductases), while other skeletally modified porphyrins (N-substituted porphyrins, oxophlorins) are formed purposefully (heme oxygenase) or accidently (cytochrome P45) in other metabolic cycles, most of which involve dioxygen utilization. Application of the new 2D methodology will be used to probe the electronic structure of these modified porphyrins, to understand the functional consequences of the skeletal modification, and to facilitate identification of these altered forms in proteins and in reactive model systems. Detailed studies of the coordination chemistry of important but poorly characterized iron complexes of isoporphyrins and oxophlorins will provide the basis for understanding their role in heme degradation or modification. Studies of reactive intermediates allow identification of functional forms involved in these oxidative processes. These studies will focus on models for the reactivity of coordinated alkyl peroxides, the mechanism of dioxygen """"""""insertion"""""""" into metal-carbon bonds (to form peroxide ligands), the mechanisms of oxophlorin formation and destruction, and in proteins, the identification of isoporphyrins and the site of radical delocalization in HRP-Compound I.

Agency
National Institute of Health (NIH)
Institute
National Institute of General Medical Sciences (NIGMS)
Type
Research Project (R01)
Project #
5R01GM026226-16
Application #
2174659
Study Section
Biophysical Chemistry Study Section (BBCB)
Project Start
1979-04-01
Project End
1996-03-31
Budget Start
1994-04-01
Budget End
1995-03-31
Support Year
16
Fiscal Year
1994
Total Cost
Indirect Cost
Name
University of California Davis
Department
Chemistry
Type
Schools of Arts and Sciences
DUNS #
094878337
City
Davis
State
CA
Country
United States
Zip Code
95618
Garcia, Thelma Y; Olmstead, Marilyn M; Fettinger, James C et al. (2008) Cleavage of the indium(III) octaethyloxophlorin dimer, {In(III)(OEPO)}2, with Lewis bases. Importance of outer-sphere hydrogen bonding in adduct structures. Inorg Chem 47:11417-22
La Mar, Gerd N (2007) Application of the paramagnetic dipole field for solution NMR active site structure determination in low-spin, cyanide-inhibited ferric hemoproteins. IUBMB Life 59:513-27
Rath, Sankar Prasad; Olmstead, Marilyn M; Balch, Alan L (2006) Electron distribution in iron octaethyloxophlorin complexes. Importance of the Fe(III) oxophlorin trianion form in the bis-pyridine and bis-imidazole complexes. Inorg Chem 45:6083-93
Bondarenko, Vasyl; Wang, Jingtao; Kalish, Heather et al. (2005) Solution 1H NMR study of the accommodation of the side chain of n-butyl-etiohemin-I incorporated into the active site of cyano-metmyoglobin. J Biol Inorg Chem 10:283-93
Sprutta, Natasza; Rath, Sankar Prasad; Olmstead, Marilyn M et al. (2005) Metal complexes of meso-amino-octaethylporphyrin and the oxidation of NiII(meso-amino-octaethylporphyrin). Inorg Chem 44:1452-9
Rath, Sankar Prasad; Olmstead, Marilyn M; Balch, Alan L (2004) The effects of axial ligands on electron distribution and spin states in iron complexes of octaethyloxophlorin, intermediates in heme degradation. J Am Chem Soc 126:6379-86
Rath, Sankar Prasad; Olmstead, Marilyn M; Balch, Alan L (2004) Reactions of meso-hydroxyhemes with carbon monoxide and reducing agents in search of the elusive species responsible for the g = 2.006 resonance of carbon monoxide-treated heme oxygenase. Isolation of diamagnetic iron(II) complexes of octaethyl-meso-hydro Inorg Chem 43:6357-65
Rath, Sankar Prasad; Kalish, Heather; Latos-Grazynski, Lechoslaw et al. (2004) Facile ring opening of iron(III) and iron(II) complexes of meso-amino-octaethylporphyrin by dioxygen. J Am Chem Soc 126:646-54
Kalish, Heather; Lee, Hon Man; Olmstead, Marilyn M et al. (2003) Heme cleavage with remarkable ease: paramagnetic intermediates formed by aerobic oxidation of a meso-amino-substituted iron porphyrin. J Am Chem Soc 125:4674-5
Ozarowski, Andrew; Lee, Hon Man; Balch, Alan L (2003) Crystal environments probed by EPR spectroscopy. Variations in the EPR spectra of Co(II)(octaethylporphyrin) doped in crystalline diamagnetic hosts and a reassessment of the electronic structure of four-coordinate cobalt(II). J Am Chem Soc 125:12606-14

Showing the most recent 10 out of 38 publications