Aggregation phenomena in the complexes of iron tetraphenylporphine sulfonate with bovine serum albumin.
Binding of Fe(III) meso-tetrakis(p-sulfonatophenyl)-porphyrin (FeTPPS4) to bovine serum albumin (BSA) was studied by UV-VIS absorption, fluorescence quenching, circular dichroism, 1H NMR, and ESR. At excess of BSA, the bound form of FeTPPS4 is a high-spin monomer exhibiting a Soret band at 417 nm, a broad NMR peak at 10.3 ppm, an ESR signal at g = 5.7-5.9, and a strong enhancement of magnetic relaxation of water protons. In the intermediate concentration range, a formation of nonparamagnetic bound aggregates of FeTPPS4 occurs (up to 10-15 molecules at pH 6.0) with a Soret band at 414 nm and NMR peaks at 7.0, 8.1, and 12.7 ppm. In the physiologic pH range, BSA binds the monomeric form of FeTPPS4 with an association constant of about 10(8) M-1, the affinity to oxo-dimers in solution being much lower. BSA itself is also subject to aggregation with an average aggregation number of 4-8 in the physiological pH range. It is assumed that aggregation phenomena may play an important role, both in the relaxation efficiency of metalloporphyrins as MRI contrast agents and in the blood transport of porphyrin drugs by albumins.
Tominaga
T T
TT
Instituto de Química de São Carlos, Universidade de São Paulo, Brazil.
Yushmanov
V E
VE
Borissevitch
I E
IE
Imasato
H
H
Tabak
M
M
D000818:Animals; D002417:Cattle; D002942:Circular Dichroism; D004578:Electron Spin Resonance Spectroscopy; D006863:Hydrogen-Ion Concentration; D009682:Magnetic Resonance Spectroscopy; D011166:Porphyrins / Q000378:metabolism*; D011487:Protein Conformation; D011838:Radiation-Sensitizing Agents / Q000378:metabolism*; D012709:Serum Albumin / Q000378:metabolism*; D013056:Spectrophotometry, Ultraviolet
D011166:Porphyrins; D011838:Radiation-Sensitizing Agents; D012709:Serum Albumin; C016136:tetraphenylporphine sulfonate