Article

Redox properties of cytochrome c.

Department of Chemistry, University of Modena and Reggio Emilia, Italy.
Antioxidants and Redox Signaling (Impact Factor: 7.67). 05/2001; 3(2):279-91. DOI: 10.1089/152308601300185232
Source: PubMed

ABSTRACT The redox properties of cytochromes (cyt) c, a ubiquitous class of heme-containing electron transport proteins, have been extensively investigated over the last two decades. The reduction potential (E degrees') is central to the chemistry of cyt c for two main reasons. First, E degrees' influences both the thermodynamic and kinetic aspects of the electron exchange reaction with redox partners. Second, this thermodynamic parameter is remarkably sensitive to changes in the properties of the heme and the protein matrix, and hence can be profitably used for the investigation of the solution chemistry of cyt c. This research area owes much to the exploitation of voltammetric techniques for the determination of E degrees' for metalloproteins, which dates back to the late 1970s. Since then, much effort has been devoted to the comprehension of the molecular factors that control E degrees' in cyt c, which include first coordination sphere effects on the heme iron, the interactions of the heme group with the surrounding polypeptide chain and the solvent, and also include medium effects related to the nature and ionic composition of the solvent, pH, the presence of potential protein ligands, and the temperature. This article provides an overview of the most significant advances made in this field recently.

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    • "Cytochrome c (Cyt c) is a 104-residue (MW 12.4 kDa) heme-containing globular protein of crucial importance in electron transport in mitochondria (Battistuzzi et al. 2001; Bertini et al. 2004). A variety of stress stimuli including growth factor withdrawal, heat shock, and DNA damage Venkatesan Renugopalakrishnan: Dedicated to my father, "
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    ABSTRACT: Background: Cytochrome c (cyt c) is well known for its role in mitochondrial electron transport. The redox state of cyt c has recently been linked to apoptosis. In the present study, we investigated and compared the kinetics of cyt c reduction by various thiol antioxidants. Methods: All kinetic experiments were performed by measuring spectrophotometrically the changes in absorbance at 550 nm for 2 min at 25 o C in a reaction buffer (50 mM Tris HCl, pH 7.4) containing cyt c (5 μM) and thiols (100 μM). Electrostatic effects on the rate of reduction of cyt c were determined by varying the ionic strength of the reaction buffer. The kinetic data were treated by applying a pseudo fi rst-order approximation. Results: The results show that, among all thiols studied, cysteine reduces cyt c at the highest rate. The second-order rate constant is on the order of 10 2 M -1 s -1 for cellular thiol reductants, GSH and cysteine. Most thiols of therapeutic importance exhibit extremely low reduction rates. Moreover, the rate of cyt c reduction was found to correlate negatively with the pK a of the SH group. This study further demonstrates that a complex electrostatic interaction may occur between cyt c and thiols. Conclusions: Given the high abundance of GSH in cells, our kinetic data suggest that GSH may out-compete other re-ductants for cyt c; and is therefore an important mediator of the cellular redox state of cyt c.