Binding of cationic porphyrin to human serum albumin studied using comprehensive spectroscopic methods

The interaction between cationic porphyrin, a potential valuable anti-tumor and antibiotic drug, and human serum albumin (HSA) was investigated using spectroscopy methods. The binding constants were obtained using fluorescence quenching method (KSV = (3.24 ± 0.29) × 104 M−1) and surface plasmon resonance (SPR) spectroscopy (KA = (6.287 ± 0.407) × 104 M−1). The association rate constant (ka = 1622 ± 72.9 M−1 s−1) and dissociation rate constant (Kd = 0.02589 ± 0.0024 s−1) of the binding process were also calculated. Compared with the two results, it was known that one of the binding sites was near the tryptophan residue and also there existed other binding sites. The Fourier transform infrared (FT-IR) spectroscopy and circular dichroism (CD) spectroscopy indicated that the confirmation of HSA was nearly not affected with the addition of porphyrin. © 2008 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 98:105–113, 2009