Binding of meso-tetra(4-sulfonatophenyl)porphine to haemopexin and albumin studied by spectroscopy methods

• 1.1. The interaction of haemopexin and albumin with TPPS₄ was studied by measuring the absorption and fluorescence spectra. Haemopexin was found to have one strong TPPS₄ binding center (K_a = 3 × 10⁷M^?1).
• 2.2. Haem-haemopexin complex appears to have no specific binding site for TPPS₄. Occupation of the specific binding center of haemopexin molecule by a haem abolishes TPPS₄ binding.
• 3.3. Albumin was found to possess one strong TPPS₄ binding center (K_a = 3 × 10⁶M^?1) besides two or three weak binding sites (K_a = 2 × 10⁵M^?1).
• 4.4. Haern-albumin complex possesses only one weak TPPS₄ binding site (K_a = 7 × lO⁵M^?1). These observations suggest identity of primary binding sites of TPPS₄ and haem on albumin molecule.