Electrostatic potential distribution case studies

It should be noted that in all the reported studies of the interactions between cytochrome C3 and different acidic redox partners or macro inorganic anion, always the same heme appears to be involved in the interaction. This is suggested by the analysis of the distribution of surface electrostatic potentials and, in some cases, is supported experimentally by cross-linking [Dolla et al., 1988, 1991] and extended NMR [Guerlesquin et al., 1985 Park et al., 1991 Mus-Veteau et al., 1992] experiments. 

If all the flavodoxins isolated from several species of Desulfovibrio are acidic, (low isoelectric points), the tetrahemic cytochromes cs are characterised by a wide range of pi values. The isoelectric points of the three cytochromes C3 studied in this work, D. vulgaris Miyazaki F, D, desulfuricans ATCC 27774 and D. gigas, are 9.5, 7.0 and 3.5, respectively. It is therefor interesting to compare the distribution of the electrostatic potential, over the surface of these proteins. The observed asymmetry of the surface charges was already emphasised in the case of D. vulgaris cytochrome C3 [Stewart et al., 1988] and was used as a basis to predict which of the four hemes should preferentially interact with D. vulgaris flavodoxin. 

Any fundamental study of the rheology of concentrated suspensions necessitates the use of simple systems of well-defined geometry and where the surface characteristics of the particles are well established. For that purpose well-characterized polymer particles of narrow size distribution are used in aqueous or non-aqueous systems. For interpretation of the rheological results, the inter-particle pair-potential must be well-defined and theories must be available for its calculation. The simplest system to consider is that where the pair potential may be represented by a hard sphere model. This, for example, is the case for polystyrene latex dispersions in organic solvents such as benzyl alcohol or cresol, whereby electrostatic interactions are well screened (1). Concentrated dispersions in non-polar media in which the particles are stabilized by a "built-in" stabilizer layer, may also be used, since the pair-potential can be represented by a hard-sphere interaction, where the hard sphere radius is given by the particles radius plus the adsorbed layer thickness. Systems of this type have been recently studied by Croucher and coworkers. (10,11) and Strivens (12). 

The kinetics of oxidation and reduction of [4Fe-4S] proteins by transition metal complexes and by other electron-transfer proteins have been studied. These reactions do not correlate with their redox potentials.782 The charge on the cluster is distributed on the surface of HiPIP through the hydrogen bond network, and so affects the electrostatic interaction between protein and redox agents such as ferricyanide, Co111 and Mnin complexes.782 783 In some cases, limiting kinetics were observed, showing the presence of association prior to electron transfer.783... 

It is possible to define a molecular index P for the induction term to be used in combination with the MEP Va to get a detailed description of the spatial propensity of the molecule to develop electrostatic interactions of classical type. Both functions are used under the form of an interaction with a unit point charge q placed at position r. In the case of Va this means a simple multiplication in the case of Pa there is the need of making additional calculations (to polarize the charge distribution of A). There are fast methods to do it, both at the variational level and at the PT level. The analysis of Pa has not yet extensively been used to model IND contributions to AE, and it shall not be used here. This remark has been added to signal that when one needs to develop interactions potentials for molecular not yet studied interactions including, e.g., complex solutes, the use of this approach could be of considerable help. 

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