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

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 (Ka = 3 x 10(7) M-1). 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. Albumin was found to possess one strong TPPS4 binding center (Ka = 3 x 10(6) M-1) besides two or three weak binding sites (Ka = 2 x 10(5) M-1). 4. Haem-albumin complex possesses only one weak TPPS4 binding site (Ka = 7 x 10(5) M-1). These observations suggest identity of primary binding sites of TPPS4 and haem on albumin molecule.