title: Binding of porphyrin to horseradish peroxidase: effects on structure and function.
abstract: Spectrofluorimetric and spectrophotometric studies were done to understand the binding of hematoporphyrin, a photosensitizer to horseradish peroxidase (EC1.11.1.7). The binding affinity constant (K) decreases as the state of aggregation of the porphyrin increases, while the number of binding sites (approximately 1) remains unchanged. The interaction appears to be mostly hydrophobic, entropy-driven and endothermic process. Hematoporphyrin potentiates horseradish peroxidase-catalyzed H2O2-mediated NADH oxidation, probably by porphyrin-influenced removal of superoxide radicals, which are generated in the system. Conformational change of the protein due to its interaction with porphyrin may be associated with potentiation of the catalytic activity of the enzyme.
authors.affiliation: Department of Biophysics, Molecular Biology & Genetics, University College of Science, University of Calcutta, 92, Acharyya Prafulla Chandra Road, Kolkata 700009, India.
authors.forename: Susmita
authors.initials: S
authors.lastname: Sil
authors.forename: Abhay Sankar
authors.initials: AS
authors.lastname: Chakraborti
mesh_terms: D002384:Catalysis; D002942:Circular Dichroism; D019277:Entropy; D006415:Hematoporphyrins / Q000737:chemistry*; D006735:Horseradish Peroxidase / Q000737:chemistry*; D006358:Hot Temperature; D006861:Hydrogen Peroxide / Q000737:chemistry; D007700:Kinetics; D008024:Ligands; D008027:Light; D046911:Macromolecular Substances / Q000737:chemistry; D009243:NAD / Q000737:chemistry; D017319:Photosensitizing Agents / Q000494:pharmacology; D011485:Protein Binding; D011487:Protein Conformation; D013050:Spectrometry, Fluorescence; D013053:Spectrophotometry; D013329:Structure-Activity Relationship; D013481:Superoxides; D013696:Temperature; D013816:Thermodynamics
chemical_list: D006415:Hematoporphyrins; D008024:Ligands; D046911:Macromolecular Substances; D017319:Photosensitizing Agents; D009243:NAD; D013481:Superoxides; D006861:Hydrogen Peroxide; D006735:Horseradish Peroxidase