title: Hematoporphyrin interacts with myoglobin and alters its functions.
abstract: The binding parameters of hematoporphyrin, a photosensitizing drug used in photodynamic therapy, interacting with myoglobin, an oxygen storage protein, have been studied spectrofluorometrically and spectrophotometrically. Two concentration ranges of hematoporphyrin, representing significantly monomeric and aggregated (dimeric) states have been used. The binding affinity constant (K) decreases and the possible number of binding sites (p) increases as the porphyrin changes from significantly monomeric state to predominantly dimeric state. Titration of the protein with hematoporphyrin in a spectrophotometric study (differential spectroscopy) exhibits an isosbestic point indicating a ground state complex formation. The interaction leads to a conformational change of the protein as observed in a circular dichroism study. The hematoporphyrin-myoglobin interaction causes oxygen release from the protein and it varies with the stoichiometric ratio of the porphyrin:protein. Hematoporphyrin also increases the myoglobin-catalysed hydrogen peroxide-mediated oxidation of o-dianisidine and NADH. These findings on the effects of hematoporphrin-myoglobin interaction should be given due consideration in therapeutic uses of the porphyrin and its derivatives.
authors.affiliation: Department of Biophysics, Molecular Biology and Genetics, University College of Science, Kolkata, India.
authors.forename: Susmita
authors.initials: S
authors.lastname: Sil
authors.forename: Abhay Sankar
authors.initials: AS
authors.lastname: Chakraborti
mesh_terms: D000818:Animals; D001665:Binding Sites; D002942:Circular Dichroism; D019281:Dimerization; D006415:Hematoporphyrins / Q000737:chemistry* / Q000494:pharmacology*; D006736:Horses; D006861:Hydrogen Peroxide / Q000494:pharmacology; D007700:Kinetics; D009211:Myoglobin / Q000737:chemistry* / Q000502:physiology*; D010100:Oxygen / Q000378:metabolism; D010544:Peroxidases / Q000737:chemistry / Q000378:metabolism; D017319:Photosensitizing Agents / Q000737:chemistry* / Q000494:pharmacology; D011485:Protein Binding; D011487:Protein Conformation; D017434:Protein Structure, Tertiary; D013053:Spectrophotometry; D013482:Superoxide Dismutase / Q000378:metabolism; D013997:Time Factors; D014466:Ultraviolet Rays
chemical_list: D006415:Hematoporphyrins; D009211:Myoglobin; D017319:Photosensitizing Agents; D006861:Hydrogen Peroxide; D010544:Peroxidases; D013482:Superoxide Dismutase; D010100:Oxygen