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Biomedical subjects

L I Krishtalik

Publications and source records attributed to L I Krishtalik.

29 records · Page 2Linked to original sources
PubMedDate not supplied

[Electrical fields in membrane proteins].

The electric fields created by dipoles of the peptide bonds of alpha-helices of membrane proteins are considered. It has been shown that the electric field of the alpha-helix compensates for the loss of the Born hydration energy and promotes dissociation of the carboxyl groups located at the depth of up to 5 A from the water surface. The presence of the carboxylate anion facilitates penetration of the hydronium ion into the membrane and lowers the potential barrier by 0.1-0.2 eV (depending on the membrane thickness). A three-layer model of the reaction centre of photosynthetic bacteria is proposed. An estimate of the dielectric constant of different parts of the reaction centre is obtained by means of comparison of photoinduced electrogenetic transmembrane potential displacement with structural data. Estimates of the electric potentials at the electron transfer chain cofactors induced by the alpha-helical segments of the reaction centre protein are given. It is shown that the asymmetry in the location of alpha-helices affects significantly the redox potentials of the electron carriers and lead to a kinetic advantage of the A-chain of electron transfer over the B-chain.

Electricity↗
PubMedDate not supplied

[Energy of ion pairs in proteins].

The energy of ions interaction in an ionic pair and the energy of ions transfer from water into protein at different ions disposition relative to the protein/water boundary has been considered. Ultimately, the ions transfer from aqueous phase into protein, i. e. in the medium with a low dielectric constant is energetically unfavorable and hence it cannot stabilize the protein structure by itself. For stabilization of ionic pairs in protein the action of some additional factors is necessary, in particular the action of the intraglobular electric field.

Electricity↗
PubMedDate not supplied

[Globule size and the activation energy of an enzymatic process].

The charge transfer reactions demand the polar medium reorganization the main part in the process energy being contributed by solvent reorganization. Protein globule excludes a part of the solvent from the interaction with the charge being transfered. Thus a strong decrease of the reorganization energy and hence of the activation energy is achieved (the gain of some kcal/mole). The effect rises at first rapidly with the globule radius but it becomes practically constant after some optimal radius is reached. The estimation of the optimal radius gives values of the order of magnitude of the enzymes molecule sizes.

Calorimetry↗
PubMedDate not supplied

[Intraglobular electrostatic field of an enzyme. Calculation of the dissociation constant of a protein ionogenic group. Dissociation of Asp-102 chymotrypsin].

Factors determining the change of dissociation constants of ionogenic groups upon their transfer from water into a protein globule are considered. The change of the short-range interaction is simulated with the aid of two model solvents: dimethylformamide (DMF) and formamide (FA). The change of Bornian solvation energy is calculated taking into account the interaction of ions situated inside a protein globule with the surrounding electrolyte solution. The change of ion energy due to the intraglobular electric field preexisting in the enzyme molecule is calculated. Each of the factors listed above gives a large contribution into the ion energy in the case of Asp-102 these contributions compensate each other to a great extent.

Aspartic Acid↗
PubMedDate not supplied

[Intraglobular electrostatic field of an enzyme. IV. Electrolytic dissociation of the active center of alpha-chymotrypsin].

The dissociation of the ionogenic groups of the active centre of alpha-chymotrypsin is considered taking into account effects of short- and long-range solvation and intraglobular electric field. The ionic pair Asp102-CO2-. His57-ImH+ is shown to be the most probable state of the neutral active centre of alpha-chymotrypsin, this ionic pair being stabilized substantially through electrostatic interaction of the ions. The pair dissociates releasing the proton from the N epsilon 2 atom of His57 and forming a catalytically active group Asp102-CO2-. His57-Im. The pK value approximately 7 characteristic of this acid-base equilibrium pertains to the active centre as a whole rather than to the isolated imidazolium ion. The approach developed by the authors is compared with other works in this area.

Binding Sites↗
PubMedDate not supplied

[The intraglobular electrostatic field of an enzyme. 1. The primary field created by the polypeptide core, functional groups and ions of the alpha-chymotrypsin molecule].

The electric field set up by the dipoles of peptide groups ad other dipoles at the atoms of substrate and catalytic groups of alpha-chymotrypsin is considered. It is shown that substantial electric potentials reaching some tenths of volts exist in the active center of the enzyme, the fact which must influence significantly the reactivity of corresponding groups. In contrast to low molecular weight liquids, the contribution to the total potential of dipoles located at different distances from the point under consideration often changes nonmonotonically with the distance, sometimes the predominant influence being exerted not by the nearest polar groups but by the more distant ones. The existence of electric fields having a complex spatial configuration determined by the protein structure can be defined as the effect of the polar medium preorganization. Emphasis is placed on the necessity of taking into account the polarization of the external medium by charges of protein atoms and ions (the difference of primary and secondary electric fields).

Chymotrypsin↗
PubMedDate not supplied

[The intraglobular electrostatic field of an enzyme. II. Effect of environment polarization].

The influence of polarization of surrounding medium on the intraglobular electric field of the alpha-chymotrypsin molecule is considered. The polarization is taken into account by the image charges method, the proper approximations for calculation of the fields due to intraglobular and surface charges are suggested. The polarization of surroundings does not change the qualitative picture of the electric field in the active center of the alpha-chymotrypsin molecule set up by protein dipoles, but reduces almost to zero the intraglobular field set up by surface ions.

Allosteric Site↗
PubMedDate not supplied

[Multielectron enzymatic reactions. The energy of medium reorganization].

Reasons are considered favouring the enzymatic reactions of simultaneous charge transfer in comparison to similar chemical reactions. The reorganization energy of enzymatic multielectron reactions reduces to the level usual for chemical one-electron reactions due to the action of the following factors: a) low dielectric permeability of proteins; b) large reactants radii and optimization of their ratio; c) incorporation of substrate into the coordination sphere of the charge donor; d) transition from two-centre to multi-centre processes, i.e. simultaneous participation in reaction of several donors and/or acceptors of charge.

Chemical Phenomena↗
PubMedDate not supplied

[Theory of charge transfer enzymatic reactions].

The influence on the elementary act energy of the change in the energies of reactants solvation and their coulombic interaction due to the transfer of reaction from the aqueous to nonaqueous medium of low dielectric permittivity, particularly the enzyme globule, has been considered. A quantitative calculation of the energies has been carried out for the isotropic dielectric model taking into account the distance of reacting particles from the aqueous/nonaqueous interface. It has been shown that the transfer of the reaction into protein globule leads to a large energy gain and hence accelerates the reaction considerably. This is true in the case when the absolute charge of reactants decreases in the course of the reaction for both particles or for one of them situated further from the interface.

Electron Transport↗