The Fe57 NMR spectrum of carbonmonoxymyoglobin has been reported. This is the first Fe57 NMR study of a protein. A new two-dimensional (2D) NMR technique has been developed for the determination of spin connectivity in homonuclear coupled spin systems. The new method relies on a different mechanism than all other 2D techniques, and has a significant number of advantages: net magnetization transfer between coupled spins is obtained which permits the recording of high resolution absorption mode spectra and provides improved sensitivity. Relayed connectivity can be observed by a judicious choice of the mixing period. Preliminary experimental results, obtained for a number of small proteins (lysozyme, ribonuclease, bovine trypsin inhibitor and myoglobin) suggest that the method is superior to existing competitive techniques. The method appears also very useful for the resonance assignment in H1 spectra of oligosaccharides and other organic products with complex NMR spectra. A number of improvements for existing one- and two-dimensional experiments have been proposed and optimization criteria have been developed for three rather complex 2D experiments: (a) homonuclear relayed coherence transfer spectroscopy, (b) heteronuclear relay spectroscopy and (c) spin-locked NOE measurements. New NMR techniques have been used to determine the previously unknown structure of the tetraene antibiotic, amphotericin A.
