Proton NMR investigation of heme and surrounding proton in low-spin cyanide-ligated bacterial hemoglobin fromVitreoscilla
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1H NMR spectra of low-spin cyanide-ligated bacterial hemoglobin fromVitreoscilla (VtHb-CN) are reported. The assignments of the1H NMR spectra of VtHb-CN have been made through MCOSY, NOESY, 1D TOE and SUPERWEFT experiments. Almost all resonance peaks of heme and ligated His85 are identified. The spin-lattice relaxation timeT 1’s and the variation relationships of chemical shifts of these peaks with temperature have been acquired, from which the distances between the measured protons and Fe3+, and the diamagnetic chemical shifts have been acquired, respectively. The ionization constants of pK a’s of ligated His85 are determined through pH titration of chemical shift, which is 4.95 for ligated His85 C2H proton. The lower pK a is attributed to the influence of the Fe3+ of carrying positive charge and the coordination of His85 and Fe3+ of heme.
Keywordshemoglobin VtHb-CN NMR relaxation pKa
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