title: Temperature dependent soret spectral band shifts accompany human CN-mesohemoglobin assembly.
abstract: The interaction between human apohemoglobin A and CN-Mesohemin, a monomeric non-native heme derivative, was probed by Soret spectrophotometric titrations in 0.05 M potassium phosphate buffer, pH 7 at varied temperatures. Hypsochromic shifts in the absorbance maxima were observed at all temperatures below 10 degrees C. First derivative spectroscopy of CN-Mesohemin titrations was used to provide further evidence of a spectral shift upon CN-Mesohemoglobin assembly. Findings of Soret Spectral shifts demonstrate a preference for the alpha chain heme site by CN-Mesohemin indicative of semi-alpha-hemoglobin intermediate formation. CN-Mesohemin, a derivative with peripheral 2,4 ethyl groups, does not possess the extended conjugation seen for native CN-Protohemin with its 2,4 vinyl groups. Indeed, reduced polarity of CN-Mesohemin over that of CN-Protohemin resulted in distinct temperature dependencies. Molecular visualization and protein-ligand interaction analysis targeted a functionally diverse residue unique to the alpha-chain. Tyrosine-42 (a polar/non-polar amino acid) appeared to play a prominent role in the assembly process.
authors.affiliation: Department of Chemistry, University of Massachusetts, Lowell, MA 01854, USA.
authors.forename: Priyani V
authors.initials: PV
authors.lastname: Fonseka
authors.forename: Gayathri
authors.initials: G
authors.lastname: Vasudevan
authors.forename: Lisa-Jo Ann
authors.initials: LJ
authors.lastname: Clarizia
authors.forename: Melisenda J
authors.initials: MJ
authors.lastname: McDonald
mesh_terms: D000495:Allosteric Site; D001059:Apoproteins / Q000737:chemistry; D002021:Buffers; D006441:Hemoglobin A / Q000737:chemistry; D006454:Hemoglobins / Q000737:chemistry*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D008024:Ligands; D008954:Models, Biological; D008958:Models, Molecular; D008968:Molecular Conformation; D011485:Protein Binding; D011506:Proteins / Q000737:chemistry; D013053:Spectrophotometry; D013696:Temperature
chemical_list: D001059:Apoproteins; D002021:Buffers; D006454:Hemoglobins; D008024:Ligands; D011506:Proteins; C023478:apohemoglobin; D006441:Hemoglobin A