Abstract
In order to investigate the effect of the alpha beta subunit contacts on the subunit structure of human adult methemoglobin, the hyperfine shifted proton NMR spectra of several high spin complexes (water, cyanate, thiocyanate, formate, fluoride, and nitrite) and low spin complexes (imisazole, azide, and cyanide) of hemoglobin and its isolated subunits were characterized at 220 MHz and 22 degrees C. The spectra of ferric low spin derivatives of the isolated subunits were approximately superimposable on the corresponding hemoglobin spectra. On the other hand, the high spin spectra of the isolated subunits were greatly different from each other. The spectral anomaly in the ferric high spin complexes of the isolated beta subunit were interpreted to indicate other structural change than the hemichrome formation in the beta heme pocket. Difference in the subunit association effect between the high and low spin complexes of the isolated beta subunit was interpreted on the basis of a conformational change of the apoprotein dependent on the spin state of the beta heme iron.
Highlights
In order to investigate the effect of the aP subunit contacts on the subunit structure of human adult methemoglobin, the hyperfine shifted proton NMR spectra of several high spin complexes and low spin complexes of hemoglobin and its isolated subunits were characterized at 220
The resonances whose chemical shifts are given in parts per million units have been assigned to the heme methyl proton resonances for the cyanide [6] and azide (l&19) complexes
Ferric Low Spin Derivatives-From the present results on the proton NMR spectra of the ferric low spin complexes of methemoglobin, it was generally shown that the chemical shifts of the a and fi heme methyl resonances are not identical, indicating the structural nonequivalence of the a and p heme environments in ferric low spin state
Summary
In order to investigate the effect of the aP subunit contacts on the subunit structure of human adult methemoglobin, the hyperfine shifted proton NMR spectra of several high spin complexes (water, cyanate, thiocyanate, formate, fluoride, and nitrite) and low spin complexes (imidazole, azide, and cyanide) of hemoglobin and its isolated subunits were characterized at 220. The spectral anomaly in the ferric high spin complexes of the isolated p subunit were interpreted to indicate other structural change than the hemichrome formation in the fi heme pocket. Difference in the subunit association effect between the high and low spin complexes of the isolated p subunit was interpreted on the basis of a conformational change of the apoprotein dependent on the spin state of the p heme iron. Yonetani et al [9] and Perutz et al [10] later pointed out that the increased low spin character observed in the aquomet /3 subunit spectra is attributable to the direct and reversible ligation of the distal histidyl residue to the ferric heme iron to form a low spin compound designated as hemichrome
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