Affiliations: Faculty of Science, Laboratory of Physical Chemistry, Department of Chemistry, University of Guilan, Rasht, Iran | Laboratory of Biophysical Chemistry, Department of Chemistry, University of Isfahan, Isfahan, Iran
Note: [] Corresponding author: Hamid Dezhampanah, Faculty of science, Laboratory of Physical Chemistry, Department of Chemistry, University of Guilan, P.O. Box 41335-1914, Rashat 0098, Iran. Tel.: +98 131 3243630 5; Fax: +98 131 3233262; E-mails: h.dpanah@guilan.ac.ir and h_dpanah@yahoo.com
Abstract: The interaction of a water-soluble cationic porphyrin, Cobalt(III) 5, 10, 15, 20-tetrakis (1-methylpyridinium-4-yl) porphyrin [Co(III)TMPyP], with bovine serum albumin (BSA) has been studied in 1 mM phosphate buffer pH 7.0 containing 5 mM NaCl by UV-vis absorption, resonance light scattering (RLS) and fluorescence spectroscopies at 25°C. The results of RLS studies represent no aggregate formation of porphyrin in the surface of BSA and low tendency of this porphyrin for aggregate formation. The binding of porphyrin complex to BSA quenches fluorescence emission of BSA via a dynamic mechanism and the quenching process obeys a linear Stern-Volmer relationship. The values of Stern-Volmer constants, KSV, was determined nearly 105 M−1, that depend on BSA concentration. The average aggregation number of BSA calculated from the analysis of fluorescence quenching data indicates that absence of any porphyrin induced aggregation of BSA due to its interaction with porphyrin complex. The binding of Co(III) TMPyP had no obvious effect on the molecular conformation of the protein. Electrostatic force played an important role in the binding due to the opposite charges on porphyrin and the protein.
Keywords: Porphyrin, serum albumin binding, fluorescence quenching, optical absorption
