NMR STUDIES OF RESPIRATORY PROTEINS AND MODEL SYSTEMS

本研究的目的是为了更好地了解

The objective of this research is to obtain a better understanding of the structure, and structure-function relations, of a variety of oxygen-transport and oxygen-storage proteins of importance in pulmonary function and disease. Initial emphasis will be placed on analysing the nature of Fe-02 bonding in hemoglobin and myoglobin. Additional studies will be aimed at solving the nature of Fe-0 bonding in the invertebrate oxygen carrier hemerythrin. Particular emphasis will be placed on recording and analyzing the iron-57 and oxygen-17 nuclear magnetic resonance (NMR) spectra of these systems using 57Fe and 170-labelled species, such as picket-fence porphyrins. In this way, we can directly probe the nature of Fe-0 bonding by analysis of iron-57 chemical shifts (sigma i), chemical shielding tensors (delta sigma; sigma 11, sigma 22, sigma 33), oxygen-17 chemical shifts of both bridging (Fe-0-0; Fe-0-Fe) and non-bridging (Fe-0-0) oxygens, together with their nuclear quadrupole coupling constants (e2qQ/h) and electric field gradient tensor asymmetry parameters (eta). Analysis of the e2qQ/h and eta information will use a Townes-Daily approach (recently applied to Si0-2), and analysis of both quadrupole and chemical shift data will also use empirical and non-empirical (initio) methods. We will first determine the 57Fe chemical shift ranges and relaxation mechanisms in a series of model compounds, including e.g. picket fence porphyrins (e.f. (2-methylimidazole)-meso-tetra (alpha,alpha,alpha,alpha,-0-pivalamidophenyl)porphyrinato iron(II) 02) using high-field Fourier transform and continuous-wave methods. These experiments will provide a data base for analysis of Hb and Mb systems. They will then be extended to investigation of paramagnetic and antiferromagnetically coupled models for hemerythrin. The solution experiments will be supplemented with solid-state magic-angle spinning experiments, to yield values of the chemical shift anisotropy. Similar model system studies are planned for 170-labelled systems, yielding in this case both isotropic chemical shift and electric field gradient tensor information. Nuclear quadrupole resonance using double-resonance level-crossing experiments will also be performed. Using this data base, we will then obtain and interpret the iron-57 and oxygen-17 NMR (and NQR) spectra of Mbo-2, Hbo-2, Hro-2, and related systems. Such results should provide valuable data with which to test the various theories (Weiss, Pauling, Case-Karplus, Olafson-Goddard) of Fe-0 bonding in hemme proteins.