title: Kinetics and mechanism of electron transfer between meso-tetra sulphonated phenyl porphyrin iron(III)-apomyoglobin and Fe(EDTA)2- complexes.
abstract: The kinetics of electron transfer between Fe(EDTA)2- and meso-tetra sulphonated phenyl porphyrin iron(III)-apomyoglobin have been studied by applying stopped-flow mixing and monitoring photometric changes at soret band (429 nm). The studies were carried out at pH's 6, 6.5, 7, 7.5, and 8 and at temperature between 10 and 40 degrees C. The mechanism proposed on the basis of the dependence of kobsd on Fe(EDTA)2- concentrations at various pH's, followed the rate equation: kobsd = ka[H+] + Kakb/[H+] + Ka.[Fe(EDTA)2-] The values of rate parameters calculated using a weighted non-linear least-squares analysis were: ka, 528 +/- 2 sec-1; kb, 25 +/- 1 sec-1; and Ka, 2.0 +/- 0.1 microM at 25 degrees C and 0.5 M sodium phosphate, and those of thermodynamic parameters calculated by the Eyring equation were: delta H*, 8.1 +/- 0.3 kcal mole-1 and delta S*, -23.4 +/- 1.1 eu at pH 7 and 0.5 M sodium phosphate.
authors.forename: S C
authors.initials: SC
authors.lastname: Tyagi
mesh_terms: D000818:Animals; D001059:Apoproteins; D004492:Edetic Acid; D005290:Ferric Compounds; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D009211:Myoglobin; D010084:Oxidation-Reduction; D011166:Porphyrins; D013696:Temperature
chemical_list: D001059:Apoproteins; D005290:Ferric Compounds; D009211:Myoglobin; D011166:Porphyrins; C010857:apomyoglobin; C016136:tetraphenylporphine sulfonate; D004492:Edetic Acid; C019179:Fe(III)-EDTA