Proton nuclear magnetic resonance studies of isonitrile-heme protein complexes.

摘要: Steric interactions between bound ligand molecules and the valine E11 methyl groups of human hemoglobin sperm whale myoglobin have been examined directly by high resolution NMR techniques. The proton resonances this amino acid are shifted markedly upfield away from bulk protein shielding effect circulating pi electrons in porphyrin ring. We monitored resonance presence CO a series isonitriles found considerable shifts its position, both various complexes among different liganded states. ring current gamma 1-methyl group Val forms isolated alpha beta chains -2.70, -2.91, -3.30 ppm, respectively. In all proteins, these positions show little change going to ethyl isocyanide. subunits myoglobin, n-propyl n-butyl isocyanide binding produces marked decreases magnitude shifts, indicating that residue has forced center large molecules. case subunits, however, only tert-butyl decrease (from -2.91 -1.99 ppm) shift protons. New peaks were observed isonitrile-protein spectra identified as comparing normal totally deuterated isonitrile complexes. magnitudes for terminal protons suggest linear geometry Fe equal C N - bonds bent chains. appears be dictated position which is located further up heme plane but closer than corresponding subunit residue. free energy changes two nearly identical, suggesting geometries energetically equivalent. Myoglobin exhibit intermediate those subunits. Assignment alkyl longer more difficult.