Pulse radiolysis kinetics of the reaction of hydrated electrons with ferric-, ferrous-, protoporphyrin IX- and apo-myoglobin

Radiation-induced enhancement of nitrite reducing activity of cytochrome c

Commercial cytochrome c (Cyt c) was irradiated with Co-60 gamma-rays in the dose range of up to 3.0 kGy to investigate the enhancement of the nitrite reducing activity of Cyt c. The optimum irradiation dose to induce nitrite reducing activity for 30 muM Cyt c solution was 1.0 kGy under an O(2) atmosphere. The nitrite reducing activity of Cyt c irradiated at this dose was approximately 45-fold that of unirradiated Cyt c and ca. 1.2-fold that of nitrite reductase. The irradiation treatment resulted in unfolding of the peptide chain, exposure of the heme group, oxidation of methionine to methionine sulfoxide, dissociation of the sixth ligand (Met), and occurrence of autoxidation in Cyt c. Sepharose-immobilized irradiated Cyt c had a similar activity to that in solution. The resin retained the activity after five uses even after 1 year of storage. The irradiated Cyt c will be able to be used as a substitute for nitrite reductase.

Parameters controlling the kinetics of ferric and ferrous hemeproteins reduction by hydrated electrons

To clarify the processes of hemeproteins reduction, three classes of these proteins (ferric, ferrous and desFe) were reduced by hydrated electrons generated by pulse radiolysis. Spectral and kinetic investigations were made on alpha hemoglobin chain and myoglobin. Human alpha chain has been chosen to avoid all ferric contaminations and horse ferric myoglobin to eliminate all ferrous protein fractions. We have successively studied the influences of: the iron presence, its oxidation state (II and III), the protein charge and the iron-ligand nature (H2O, OH-, N3- and CN-). For alpha human hemoglobin chain without metallic ion or with ferrous iron, the reduction rates are the same: 1.1 +/- 0.2.10(10) M-1.s-1. In the case of horse ferric myoglobin, the reduction rates depend principally on the protein charge (from pH 6.3 to pH 9.5, the reduction rate of Mb(FeIII)N3- decreases from 2.5 +/- 0.5.10(10) M-1.s-1 to 1.2 +/- 0.2.10(10) M-1.s-1) and are also modulated by the equilibrium constant of the hemeprotein-ligand association (1.2 +/- 0.2.10(10) M-1.s-1 for Mb(FeIII)N3- and 0.8 +/- 0.2.10(10) M-1.s-1 for Mb(FeIII)CN-, at pH 9.8).