PubMed Health⌕ Search

Biomedical subjects

A A Kononenko

Publications and source records attributed to A A Kononenko.

At least 37 records · Page 2Linked to original sources
PubMed1979

Bacteriorhodopsin (BR570) bathochromic band shift in an external electric field.

In dry films of bacteriorhodopsin-containing purple membranes from Halobacterium halobium the external electric field (10(4) -- 10(5) V . cm-1) induces the appearance of a product spectrally close to the initial intermediate of bacteriorhodopsin (BR) photochromic cycle (bathoform, K). This result and also preliminary data of the electret-thermal analysis of the preparations suggest that the dielectric polarization in chromophore-protein-lipid complexes might be an essential step of the primary stabilization of light energy in photo-bioenergetic processes.

Bacteriorhodopsins↗
PubMed1979

[Electron acceptors in photosynthetic reaction centers from Rhodopseudomonas spheroides].

Using optical differential spectroscopy and EPR, a parallel study of light-induced electron transfer between the primary (X1) and secondary (X2) quinone-like acceptors in the preparations of reaction centers (RC) isolated from bacterial chromatophore membranes with sodium dodecyl sulfate was carried out. The data from direct measurements of the rate constant temperature dependence for the interaction between light-reduced X1 and X2 (KX1X2) are in good agreement with the data calculated from the kinetic analysis of dark reduction of photooxidized bacteriochlorophyll RC on the acceptors X1 and X2 (KX1X2 = 2.10(-1)S at 20 degrees; Ea = 11,8 kcal.mol-1 within the temperature range of 20 degrees-- -20 degrees). This evidence proves the efficiency of the previously used approach /1, 2/ for the evaluation of the X1-X2 interaction. The method proposed was used for a kinetic analysis of a low-temperature electron transfer from X1 to X2 in RC isolated with lauryldimethylaminoxide (KX1X2 = 2,3.10(2) S-1 at 20 degrees; Ea = 5,5 kcal.mol-1 within the temperature range of 10 degrees-- --70 degrees).

Bacterial Chromatophores↗
PubMed1978

Electric field-induced polarization of photosynthetic membranes and reaction centers of Rhodopseudomonas sphaeroides, strain 1760-1.

Electric fields of 10(5) V/cm cause the polarization of chromatophore and reaction center films prepared from photosynthesizing purple bacteria. Photosynthetic pigments, and in particular carotenoids, the absorption spectra of which are changed in response to electric fields (electrochromism), may serve as intrinsic indicators of the development of a polarized state. Polarization occurs due to changes in the orientation and the spatial position of different charged groups and particles. The field-induced polarized state can be fixed by exposure to low temperature (-120 degrees C). On being heated, the system relaxes to the initial state and this can be seen as a thermodepolarization current in an electric circuit. The effects of hydration, chemical modification or heat treatment on thermodepolarization current indicate the involvement of macromolecular components in the formation of a polarized state. In light-adapted samples the polarization effect is markedly greater, indicating that conformational changes occur during the primary photoact. It is assumed that the polarization of the reaction centers during electron transfer might be involved in the stabilization of separated charges and in the storage of energy.

Bacterial Chromatophores↗
PubMed1976

New experimental approach to the estimation of rate of electron transfer from the primary to secondary acceptors in the photosynthetic electron transport chain of purple bacteria.

A method for calculating the rate constant (KA1A2) for the oxidation of the primary electron acceptor (A1) by the secondary one (A2) in the photosynthetic electron transport chain of purple bacteria is proposed. The method is based on the analysis of the dark recovery kinetics of reaction centre bacteriochlorophyll (P) following its oxidation by a short single laser pulse at a high oxidation-reduction potential of the medium. It is shown that in Ectothiorhodospira shaposhnikovii there is little difference in the value of KA1A2 obtained by this method from that measured by the method of Parson ((1969) Biochim, Biophys. Acta 189, 384-396), namely: (4.5 +/- 1.4)-10(3) s-1 and (6.9 +/- 1.2)-10(3) s-1, respectively. The proposed method has also been used for the estimation of the KA1A2 value in chromatophores of Rhodospirillum rubrum deprived of constitutive electron donors which are capable of reducing P+ at a rate exceeding this for the transfer of electron from A1 to A2. The method of Parson cannot be used in this case. The value of KA1A2 has been found to be (2.7 +/- 0.8)-10(3) s-1. The activation energies for the A1 to A2 electron transfer have also been determined. They are 12.4 kcal/mol and 9.9 kcal/mol for E. shaposhnikovii and R. rubrum, respectively.

Bacterial Chromatophores↗