title: Photoreduction of autooxidized albumin-heme hybrid in saline solution: revival of its O(2)-binding ability.
abstract: Recombinant human serum albumin (rHSA) incorporating 2-[8-[N-(2-methylimidazolyl)]octanoyloxymethyl]-5,10,15,20-tetrakis(alpha,alpha,alpha,alpha-o-pivalamido)phenylporphinatoiron(II)s (Fe(II)Ps) [rHSA-Fe(II)P] is a synthetic hemoprotein which can bind and release O(2) reversibly under physiological conditions (saline solution [NaCl]: 150 mM, pH 7.3) as do hemoglobin and myoglobin. However, the central ferrous ions of Fe(II)Ps are slowly oxidized to O(2)-inactive ferric forms. Based on the UV-vis. absorption spectroscopy, the majority of the autooxidized Fe(III)Ps in albumin are determined to be six-coordinate high-spin complexes with a proximal imidazole and a chloride anion, which show ligand-to-metal charge transfer (LMCT) absorption at 330 nm. Interestingly, photoirradiation of this LMCT band under an argon atmosphere led to reduction of the central ferric iron of Fe(III)P, allowing the revival of the O(2)-binding ability. The ratio of the photoreduction reached a maximum of 83%, which is probably due to the partial dissociation of the axial imidazole. The same photoirradiation under a CO atmosphere provides the corresponding carbonyl rHSA-Fe(II)P. Laser flash photolysis experiments revealed that the reduction was completed within 100 ns. The quantum yields (Phi) of these photoreductions were approximately 0.01.
authors.affiliation: Department of Polymer Chemistry, Advanced Research Institute for Science and Engineering, Waseda University, Tokyo 169-8555, Japan.
authors.forename: A
authors.initials: A
authors.lastname: Nakagawa
authors.forename: T
authors.initials: T
authors.lastname: Komatsu
authors.forename: E
authors.initials: E
authors.lastname: Tsuchida
mesh_terms: D002248:Carbon Monoxide / Q000378:metabolism; D006418:Heme / Q000737:chemistry* / Q000378:metabolism; D006420:Hemeproteins / Q000138:chemical synthesis* / Q000378:metabolism*; D006454:Hemoglobins / Q000378:metabolism; D006801:Humans; D007093:Imidazoles / Q000737:chemistry; D008665:Metalloporphyrins / Q000737:chemistry / Q000378:metabolism; D009211:Myoglobin / Q000378:metabolism; D010084:Oxidation-Reduction; D010100:Oxygen / Q000378:metabolism*; D010782:Photolysis / Q000528:radiation effects; D011994:Recombinant Proteins / Q000737:chemistry; D012709:Serum Albumin / Q000737:chemistry* / Q000378:metabolism; D012965:Sodium Chloride / Q000737:chemistry / Q000378:metabolism
chemical_list: D006420:Hemeproteins; D006454:Hemoglobins; D007093:Imidazoles; D008665:Metalloporphyrins; D009211:Myoglobin; D011994:Recombinant Proteins; D012709:Serum Albumin; D006418:Heme; D012965:Sodium Chloride; C029899:imidazole; D002248:Carbon Monoxide; D010100:Oxygen