¹³C nuclear magnetic resonance studies of the binding of isocyanides to various hemoglobins and myoglobins

Abstract

Interactions between ethyl and isopropyl isocyanides and various hemoglobins and myoglobins have been studied by 13C nuclear magnetic resonance. The results indicate that the chemical shift of the bound isocyanide depends on the structure of the hemoglobin subunit or myoglobin. The resonances exhibited by isocyanides bound to myoglobin are sensitive to pH in contrast to the situation with rabbit and human hemoglobins. beta subunits of opossum, rabbit, and human hemoglobins show a significantly greater preferential affinity for CO relative to EIC than do alpha subunits which have allowed the assignment of resonances. Rabbit, human, and opossum hemoglobin subunits bind ethyl isocyanide without observable preferences and an excess of DPG does not appear to affect this random order of ligation. In contrast, an excess of IHP seems to cause preferential ligation of the alpha subunits in these hemoglobins. The results have been used to gain insights into the differing characteristics of the ligand binding pockets of these various hemoglobins.

Carbon-13 nuclear magnetic resonance study of the motional behavior of ethyl isocyanide bound to myoglobin and hemoglobin

“…The NMR spectra for human hemoglobin (Figures 1 and 2) show chemical shifts for bound [1-13C]-and [2-l3C]ethyl isocyanide almost identical with those of myoglobin. No separate a and ß chain peaks are visible, although they are seen for ethyl [13C]isocyanide (Mansuy et al, 1976(Mansuy et al, , 1978Dill et al, 1978). One concludes from these observations that the heme environment experienced by the ethyl side chain of ethyl isocyanide is similar in harbor seal and sperm whale myoglobin and fully liganded human hemoglobin.…”

Isonitriles (Isocyanides) as Model Compounds in the Investigation of the Reaction Mechanism and Kinetics of the Ligands Withhemeiron Inhemoglobins, Myoglobins, and Cytochromes

“…Interactions between EtNC and iPrNC and various Hbs and Mbs by °C NMR have been studied byDill and coworkers [23]. Their results indicate that the chemical shift of the bound isonitrile depends on the structure of the Hb subunit…”