Redox components

Contrary to theory the value of y oo depends on the concentration ration of the redox components with values ranging from 34. 3 Solution saturated with benzene. 

All these latter centers were seen to titrate at around 150 mV, that is, some 150 mV lower than the traditional centers, and thus form a separate subclass of this type of redox proteins (see Fig. 7). Since similar downshifts were observed for almost all redox components in the mentioned species (for a compilation, see 133), it is generally assumed that the differences between the two groups represent an adaptation to the difference in value of the quinone pool, which is plastoquinone(PQ)/ubiquinone(UQ) E 100 mV) in the traditional species and menaquinone (MK) Em,i---70 mV) in the other... 

Reed, C.A. Iron(l) and iron(lV) porphyrins. In Kadish, K.M. (ed.) Electrochemical and Spectrochemical Studies of Biological Redox Components, pp. 333-356. American Chemical Society (1982)... 

Chazotte, B., and Hackenbrock, C.R. (1991) Lateral diffusion of redox components in the mitochondrial inner membrane is unaffected by inner membrane folding and matrix density./. Biol. Chem. 266, 5973. 

Birke, R.L., Lombardi, J.R., and Sanchez, L.A. In Electrochemical and Spectroscopic Studies of Biological Redox Components Kadish, K. Ed. ACS Symposium Series No.210 ... 

Taniguchi V, Ellis W, Cammarata V, Webb J, Anson F, Gray HB (1982) In Kadish K (ed) Electrochemical Studies of Biological Redox Components, American Chemical Society, Washington, DC, ACS Adv Chem Ser 201, p 51... 

That the Mn402 is capable of adopting at least three isolable oxidation levels thus lends support, albeit circumstantial, to the possibility that it is to be found as the redox component in the WOC, if only at the lower S states. In support of this, the various oxidation levels of the synthetic materials have been found to be electrochemically interconvertible, and a [Mn402] level has been detected electrochemically (31). 

Riboflavin is the redox component of flavin adenine dinucleotide FAD. It is derived from FAD by hydrolysis of a phosphate ester link. The fully oxidised form of FAD is involved in many dehydrogenaze reactions during which it is converted to the fully reduced form. The fully oxidised state is restored either by another redox enzyme or by interaction with oxygen and hydrogen peroxide is liberated. The one-electron reduced, semiquinone form of FAD, is involved in some electron transfer steps. 

Inhibition of whole chain electron transport can result from (a) Interaction of the inhibitor with a redox component of the pathway or (b) interaction with carrier systems that transport substrate molecules across the inner membrane. The latter interaction could be direct or indirect. Because electron transport associated with the oxidation of malate, succinate, and exogenous NADH were all inhibited, but to differing extents, a specific Interaction with a single redox component of the inner mitochondrial membrane does not seem to be involved. 

Petroulas, V., and Diner, B. A. (1990). Formation by NO of nitrosyl adducts of redox components of the photosystem 11 reaction center. 1. NO binds to the acceptor-side non-heme iron. Biochim. Biophys. Acta 1015, 131-140. 

Several strategies for the attachment of redox components onto a host surface are, in principle, feasible, among them chemisorption, electrostatic association, hydrogen-bonding, physisorption, and physical entrapment [32]. Because... 

The final group of mitochondrial redox components are one-electron carriers, small proteins (cytochromes) that contain iron in the form of the porphyrin complex known as heme. These carriers, which are discussed in Chapter 16, exist as several chemically distinct types a, b, and c. Two or more components of each type are present in mitochondria. The complex cytochrome aa3 deserves special comment. Although cytochromes are single-electron carriers, the cytochrome aa3 complex must deliver four electrons to a single 02 molecule. This may explain why the monomeric complex contains two hemes and two copper atoms which are also able to undergo redox reactions.1 2... 

Although normal pulse polarography was developed mainly for analytical purposes, it is a valuable and simple method to study kinetics of not-too-fast electrode reactions. As the other controlled potential techniques, it has the advantage of being applicable to systems where only one of the redox components is present initially. The technique is closely related to d.c. polarography [11] and the expressions discussed in this section are directly applicable to the case of d.c. polarography performed with the static mercury drop electrode (SMDE) if the correction for the spherical shape of this electrode is negligible [21, 22]. 

Controlled-current chronoabsorptometry involves the simultaneous optical monitoring of the product or other redox component in the electrode mechanism during a chronopotentiometry experiment [14]. Although this technique has been demonstrated with Sn02 optically transparent electrodes, it has generally received little use, since the resistance effects in thin-film electrodes can give unequal current densities across the electrode face. This results in distorted potential-time and absorbance-time responses. Consequently, the more prevalent spectro-electrochemical methods utilize potential rather than current as the excitation signal. 

Equilibrium models are powerful tools for describing the conditions of stability of redox components in natural water systems. More extended quantitative inferences must be made with great caution because the systems are generally dynamic rather than equilibrated. 

The other classes of flavoproteins in table 10.2 interact with molecular oxygen either as the electron-acceptor substrates in redox reactions catalyzed by oxidases or as the substrate sources of oxygen atoms for oxygenases. Molecular oxygen also serves as an electron acceptor and source of oxygen for metalloflavoproteins and dioxygenases, which are not listed in the table. These enzymes catalyze more complex reactions, involving catalytic redox components, such as metal ions and metal-sulfur clusters in addition to flavin coenzymes. 

We are currently exploiting the unique ability to control the architecture in these monolayers to further investigate their photoelectrochemical properties with respect to such factors as light intensity, solution and film redox components, assembly structure, dye orientation, etc. We are particularly interested in using the monolayer structural information we now have to correlate film electronic properties with charge transfer effects at both the dye-solid and dye-liquid interfaces. 

The frequent association of electron-transfer proteins with membranes reflects the important role of the membrane in controlling the orientation of the proteins for fast electron transfer. It ensues that electron transfer utilizes all the redox components and does not bypass electron-transfer proteins having associated essential functions such as proton pumping. The existence of such gradients associated with electron transfer would not be possible in the absence of the membrane. 

---