Studies on nitrosyl hemes in Ni(II)–Fe(II) hybrid hemoglobins |
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Authors: | Swarnalatha Venkateshrao Balan Venkatesh Periakaruppan T. Manoharan |
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Affiliation: | Department of Chemistry and Sophisticated Analytical Instrumentation Facility, Indian Institute of Technology, Madras, Chennai 600 036, India. |
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Abstract: | Subunit heterogeneity within a particular subunit in hemoglobin A have been explored with electron paramagnetic resonance spectroscopy using the nitrosyl hemes in Ni-Fe hybrid Hb under various solution conditions. Our previous studies on the crystal structure of NiHb demonstrated the presence of subunit heterogeneity within alpha-subunit. To further cross check this hypothesis, we made a hybrid Hb in which either the alpha- or beta-subunit contains iron, which alone can bind to NO. By this way dynamic exchange between penta- and hexa-coordinated forms within a subunit was confirmed. Upon the addition of inositol hexa phosphate (IHP) to these hybrids, R to T state transition is observed for [alpha(2)(Fe-NO)beta(2)(Ni)] but such a direct transformation is less marked in [alpha(2)(Ni)beta(2)(Fe-NO)]. Hence the bond between N(epsilon) and Fe is fundamental to the structure-function relation in Hb, as the motion of this nitrogen triggers the vast transformation, which occurs in the whole molecule on attachment of NO. |
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Keywords: | Hemoglobin Nitric oxide Hybrid hemoglobin EPR Heme–iron nitrosyl complex |
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