Effects of Net and Local Charges on the Interaction between Chemically-Modified Horse Heart Cytochrome c and P700 in Photosystem 1-Enriched Subchloroplast Particles

2-Hydroxy-5-nitrobenzyl bromide reacts with horse heart cytochrome c at acid pH to yield a chemically modified protein. Chromatography of the protein on CM-cellulose allows separation of a single chemically modified species. This species is shown by gel chromatography to be monomeric, and isoelectric focusing shows the pI to be lowered from 10.5 to 9.8 on introduction of the reagent molecule. The changes observed in the u.v. region of the spectrum are consistent with the introduction of a single residue of the reagent, and the normal fluorescence of tryptophan is lost. The chemically modified protein exhibits marked changes in its functional properties as compared with native cytochrome c. Unlike the native monomer, the modified cytochrome c has a pH-dependent spectrum which is typical of a high-spin species in the alpha/beta region at low pH, changing to a low-spin species with an apparent pK of 7.5. The modified protein is autoxidizable and the ferrous form binds CO at neutral pH with an affinity constant of 2.6 X 10(5)M-1. The ferrous form of the modified cytochrome c binds CN- at pH 10.0 with an affinity constant of 3.5 X 10(2)M-1. The modified cytochrome c was incapable of restoring the electron-transfer activity to mitochondria depleted of cytochrome c.

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Electrochemical behaviour of horse heart cytochrome c and microperoxidase at a gold electrode chemically modified with sulphur-containing compounds

Bioelectrochemistry and Bioenergetics ◽

10.1016/0302-4598(92)80065-o ◽

1992 ◽

Vol 29 (2) ◽

pp. 177-184 ◽

Cited By ~ 16

Author(s):

Roberto Santucci ◽

Maurizio Brunori ◽

Luigi Campanella ◽

Gloria Tranchida

Keyword(s):

Cytochrome C ◽

Gold Electrode ◽

Electrochemical Behaviour ◽

Horse Heart Cytochrome ◽

Chemically Modified ◽

Horse Heart Cytochrome C

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Kinetics and mechanism of the reaction between oxidized cytochrome c and ascorbic acid

Collection of Czechoslovak Chemical Communications ◽

10.1135/cccc19910478 ◽

1991 ◽

Vol 56 (2) ◽

pp. 478-490 ◽

Cited By ~ 2

Author(s):

Joaquin F. Perez-Benito ◽

Conchita Arias

Keyword(s):

Ascorbic Acid ◽

Cytochrome C ◽

Redox Reactions ◽

Arrhenius Equation ◽

Horse Heart Cytochrome ◽

First Order ◽

Acidic Form ◽

Ph Range ◽

Horse Heart Cytochrome C ◽

Mechanism Of The Reaction

The reaction between horse-heart cytochrome c and ascorbic acid has been investigated in the pH range 5.5 – 7.1 and at 10.0 – 25.0 °C. The rate shows a first-order dependence on the concentration of cytochrome c, it increases in a non-linear way as the concentration of ascorbic acid increases, it increases markedly with increasing pH and, provided that the ionic strength of the medium is high enough, it fulfills the Arrhenius equation. The apparent activation energy increases as the pH of the solution increases. The results have been explained by means of a mechanism that includes the existence of an equilibrium between two forms (acidic and basic) of oxidized cytochrome c: cyt-H+ -Fe3+ + OH- cyt -Fe3+ + H2O, whose equilibrium constant is (6.7 ± 1.4). 108 at 25.0 °C, the acidic form being more reducible than the basic one. It is suggested that there is a linkage of hydrogenascorbate ion to both forms of cytochrome c previous to the redox reactions. Two possibilities for the oxidant-reductant linkage (binding and adsorption) are discussed in detail.

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