Lysozyme electrostatic interaction

Lysozyme Electrostatic interactions Sodium silicate Partides [108]... 

Electron-electron repulsion integrals, 28 Electrons bonding, 14, 18-19 electron-electron repulsion, 8 inner-shell core, 4 ionization energy of, 10 localization of, 16 polarization of, 75 Schroedinger equation for, 2 triplet spin states, 15-16 valence, core-valence separation, 4 wave functions of, 4,15-16 Electrostatic fields, of proteins, 122 Electrostatic interactions, 13, 87 in enzymatic reactions, 209-211,225-228 in lysozyme, 158-161,167-169 in metalloenzymes, 200-207 in proteins ... 

Dao-pin et al. (1989) stressed that the enzymatically catalyzed hydrolysis of polysaccharides proceeds at more than five orders of magnitude faster than that for model compounds mimicking the substrate in the active site of the lysozyme. Although many workers have stressed that electrostatic interactions of specific residues with the substrate are an important feature of the mechanism, Dao-pin et al. suggest, rather, on the basis of results obtained by classical electrodynamics, that the charge distribution of the enzyme as a whole is the important feature. 

The elucidation of the X-ray structure of lysozyme provided the first direct information about the structure of an enzyme-substrate complex (Blake et al., 1967). This and other biochemical studies led to the proposal of three major catalytic factors general acid catalysis, steric strain and electrostatic stabilisation. It was found that the effect of steric strain is unlikely to be important because it can be relaxed by small shifts in the substrate and enzyme geometries (Warshel and Levitt, 1976 Pincus et al., 1977). This point was further established by quantitative FEP calculations (Warshel, 1991). On the other hand, it was found that electrostatic interactions play a very important role in the enzymatic reaction. The total electrostatic stabilisation of the carbonium transition state, relative to the corresponding stabilisation in solution, was found to be 29 kJ/mol (cf. Figure 12., Warshel, 1978). This value appears to account... 

It would be expected that the trend described above should also be verified for proteins. Goklen and Hatton confirmed this hypothesis (38, 39), at least for low molecular weight proteins. They studied the solubilization of three proteins, cytochrome C, ribonuclease and lysozyme of similar size but with distinct pi, from a 1 mg/ml aqueous protein solution into a 50 mM AOT/isooctane organic phase (figure 2) and showed that no extraction occurs for pH > pi, i.e. for pH values where the net charge of the protein is negative. As soon as the pH decreases below the pi value, there is an abrupt enhancement of the protein solubilization the surfactant and the protein bear opposite charges and electrostatic interactions become attractive. The decrease of protein solubilization at low pH values is interpreted by the authors in terms of protein precipitation at the interface due to denaturation. 

Ionic Strengths If the protein-polymer complex is formed as a result of electrostatic interactions, increased ionic strength should serve to reduce the attraction between the oppositely charged macromolecules, and decrease the precipitation efficiency. This is observed at pH 4.2 in Figures 3 and 4 for lysozyme and ovalbumin, respectively, and in Figure 5 for lysozyme at pH 5.8 and 7.5. 

Barroug, A., Lemaitre, J., and Rouxhet, P.G., Lysozyme on apatites A model of protein adsorption controlled by electrostatic interactions, Colloids Surf, 37, 339, 1989. 

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