Protein effective charge

Figure 6.9 Effect of CITREM concentration on the molecular and thermodynamic parameters of complex protein-surfactant nanoparticles in aqueous medium (phosphate buffer, pH = 7.2, ionic strength = 0.05 M 20 °C) (a) extent of protein association, k = Mwcomplex/Mwprotem (b) structure-sensitive parameter, p (c) second virial coefficient, A2 (rnolal scale) (d) effective charge, ZE (net number n of moles of negative charges per mole of original sodium caseinate nanoparticles existing at pH = 7.2 (Mw = 4xl06 Da)). The indicated cmc value refers to the pure CITREM solution. Reproduced from Semenova et al. (2007) with permission.

Electrochemical indicator methods are based on the application of redox probe that undergoes oxidation and reduction transition due to electron transfer from electrode surface to a probe. In 2005, several studies that used methylene blue (MB) as an electrochemical indicator were published. MB is positively charged low-molecular-weight compound that can be reduced by two electrons to a leucomethylene blue (LB). The reduction process can be effectively monitored, e.g., by differential pulse voltammetry or coulometry. In presence of redox probe Fe(CN)6, the LB is oxidized to MB and the system is regenerated [44,45]. In papers by Hianik et al. [31,46], MB was used as the indicator of detection of interaction of human thrombin with DNA aptamer. The method of detection is schematically shown in Fig. 33.3B. MB binds both to DNA and to the protein. For charge transfer from electrode to MB, i.e., for MB reduction, it is important that MB should be close to the electrode surface. Therefore, the charge transfer from the electrode... 

If both the analytes and the EOF move in the same direction, as with CIE, the system is classified as coelectroosmosis, and the analytes reach the detector faster than they would as a result of their own mobilities. If the analytes move in the opposite direction from the analytes, the system is classified as counterelectroosmosis, and the analytes reach the detector later than they would as a result of their own mobilities. If the EOF is suppressed by eliminating the effective charge on the capillary wall, then the analytes reach the detector solely as a result of their own mobility. The last approach is often taken for the analysis of large peptides and proteins, where ionic or hydrophobic interactions between the analyte and the capillary wall result in peak tailing or total adsorption. 

If it is assumed that the final effective charge at the macroion surface of a polypeptide or protein can be represented by Zq, where Z is the magnitude of the charge, q is the sign of the charge, r is the protein radius [calculated71 from the relationship r = (0.81 Mr1/3), then... 

Several computational models were employed in our study [35], Model I included a chromophore in gas-phase (Figure 4-10(a-d)). Model II additionally involved a point-charge model for protein electrostatic potential. In Model HI, the atoms in the active site (Figure 4-10(f)) were treated by quantum mechanics, and the rest of the protein effect was treated by the point-charge model. The structures used in Models... 

It is also important to point out that the direction of the ionic strength effect on rate constants does not always correlate with the protein net charge. Thus, in reactions with FMN [47] and flavodoxin [48], three species of cytochrome C2 having net charges of —7, 0 and -1-2 all show attractive electrostatic interactions during ET with these negatively charged species. The reason for this behavior lies in the fact... 

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