Redox potentiometry

Dutton, P.L. 1978. Redox potentiometry determination of midpoint potentials of oxidation-reduction components of biological electro-transfer systems. Methods in Enzymology 54 411 135. 

S, spectroelectrochemistry P, photochemical reduction T, reductive titration CV, cyclic voltammetry R, redox potentiometry. 

Measurements can be done using the technique of redox potentiometry. In experiments of this type, mitochondria are incubated anaerobically in the presence of a reference electrode [for example, a hydrogen electrode (Chap. 10)] and a platinum electrode and with secondary redox mediators. These mediators form redox pairs with Ea values intermediate between the reference electrode and the electron-transport-chain component of interest they permit rapid equilibration of electrons between the electrode and the electron-transport-chain component. The experimental system is allowed to reach equilibrium at a particular E value. This value can then be changed by addition of a reducing agent (such as reduced ascorbate or NADH), and the relationship between E and the levels of oxidized and reduced electron-transport-chain components is measured. The 0 values can then be calculated using the Nernst equation (Chap. 10) ... 

Studied by redox potentiometry, the components of the electron-transport chain have been assigned the E0 values shown below ... 

At this point, a brief mention will be made regarding the redox potential of the [Brb/BO"] couple. Being an early electron acceptor in bacterial reaction centers, its redox potential is an important property for the understanding of the energetics ofthe photochemical reactions. Klimov, Shuvalov, Krakhmaleva, Klevanik and Krasnovsky determined the redox potential of the [BO/BO"] couple by redox potentiometry. The approach taken was to gradually decrease in a straightforward manner the ambient... 

Alegria and Dutton used the Langmuir-Blodgett (LB) technique to deposit multiple (mono) layers of either the Rp. viridis reaction-center complex or of the corresponding chromatophores, in either case dispersed in a phospholipid matrix. The absorption spectmm of the LB-film was almost identical to that of the reaction center complex in solution, as shown in Fig. 10 (A), indicating that the in vitro properties of the photosynthetic apparatus are stable and essentially retained in the LB-films. The authors used a combination of redox potentiometry and absorption spectroscopy to identify the four Rp. viridis hemes and their redox potentials, and also determined their orientations by linear-dichroism measurements. 

Poth M, Focht DD (1985) 15N kinetic analysis of N20 production by Nitrosomonas europaea an examination nitrifier denitrification. Appl Environ Microbiol 49 1134-1141 Powell SJ, Prosser JI (1985) The effect of nitrapyrin and chloropicolinic acid on ammonium oxidation by Nitrosomonas europaea. FEMS Microbiol Lett 28 51-54 Prince RC, Hooper AB (1987) Resolution of the hemes of hydroxylamine oxidoreductase by redox potentiometry and electron spin resonance spectroscopy. Biochemistry 26 970-974 Probst I, Bruschi M, Pfennig N, LeGall J (1977) Cytochrome c-551.5(c7) from Desulfuromonas acetoxidans. Biochim Biophys Acta 460 58-64... 

Dutton PL. Redox potentiometry Determination of midpoint potentials of oxidation-reduction components. In Biological Electron Transfer Systems. In Methods in Enzymology, Biomembranes. Academic Press, 1978 411-435. 

Ironically, although XO/XDH is surely the most intensively studied Mo enzyme, its electrochemistry has proven to be quite challenging. An initial unmediated electrochemical study of bacterial [Rhodobacter capsulatus) XDH reported the redox potentials of all centres using a combination of EPR monitored redox potentiometry and cyclic voltammetry. Several non-tumover responses were identified by cyclic voltammetry of XDH adsorbed on an edge-oriented pyrolytic graphite electrode. In the absence of any mediators, but in the presence of xanthine, a pronounced catalytic anodic (oxidation) wave emerged at +400 mV vs. NHE (pH 8). The catalytic current was dependent... 

Dutton PL and Wilson DF (.1974) Redox potentiometry in mitochondrial and photosynthetic bioenergetics, Biochim. Biophys. Acta 346, 165-212. 

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