Electron transport control in chloroplasts. Effects of photosynthetic control monitored by the intrathylakoid pH

(1) In isolated chloroplasts (class B) electron flow is controlled mainly by the intrathylakoid pH (pH_in). A decrease in pH_in due to the light-driven injection of protons inside the thylakoid leads to the retardation of electron flow between two photosystems. This effect can be abolished by uncouplers or under photophosphorylation conditions (addition of Mg²⁺-ADP with P_i); Mg²⁺-ATP does not influence the steady-state rate of electron flow, (2) The steady-state pH difference, ΔpH, across the thylakoid membrane was estimated from quantitative analysis of the rate of P-700⁺ reduction. In chloroplasts, without adding Mg²⁺-ADP, ΔpH increases from 1.6 to 3.2 as the external pH rises from 6 to 9.5. Under the photophosphorylation conditions, ΔpH decreases showing a minimum at the external pH 7.5 ($\text{Δ}\text{pH}\text{? 0.5–1.0}$). (3) The value of photosynthetic control, K, measured as the ratio of the steady-state rates of P-700⁺ reduction in the presence of Mg²⁺-ADP (with P_i) and without adding Mg²⁺-ADP is dependent on external pH variations, showing a maximum value of $\text{K ? 3.5}$ at pH_out 7.5. This pH dependence coincides with that of the ADP-stimulated ΔpH decrease. (4) Experiments with spin labels provide evidence that the light-induced changes in the thylakoid membrane are sensitive to the addition of uncouplers and are affected only slightly by the addition of Mg²⁺-ADP and P_i.     

Formation of genetic polymorphism in connection with phylogenesis and microevolution of the domestic dog Canis familiaris L

The analysis of genetic relationships between numerous breeds and populations of domestic dogs of Asian and European origin was performed by studying their polymorphism for 14 loci of biochemical markers. Phylogenetic positions of different breed groups, related to one another and to ancestral forms from the center of domestication, were elucidated. Directions of gene flow in the formation of breed as well as dynamics and vectors of the forming genetic structure in microevolution of this extremely polytypic species, were established.     

Experimental study on the therapeutic effect of liposome-entrapped antibiotics in the treatment of destructive pneumonia]

The data on preparation of liposome-entrapped gentamicin sulfate and cefoperazone and their investigation on albino mice with staphylococcal destructive pneumonia are presented. Comparative study of the efficacy of gentamicin sulfate and cefoperazone in free and liposome-entrapped forms showed that immobilization of the antibiotics in phospholipid vesicles provided a 2-fold increase of their efficacy.     

Molecular evolution of ion channels: Amino acid sequences and 3D structures

Comparative analysis of structure and function of macromolecules, such as proteins, is an integral part of modern evolutionary biology. The first and critical step in understanding evolution of homologous proteins is their amino acid sequence alignment. However, standard algorithms fail to provide unambiguous sequence alignment for proteins of poor homology. More reliable results can be provided by comparing experimental 3D structures obtained at atomic resolution with the aid of X-ray structural analysis. If such structures are lacking, homology modeling is used which considers indirect experimental data on functional roles of individual amino acid residues. An important problem is that sequence alignment, which reflects genetic modifications, not necessarily corresponds to functional homology, which depends on 3D structures critical for natural selection. Since the alignment techniques relying only on the analysis of primary structures carry no information on the functional properties of proteins, the inclusion of 3D structures into consideration is of utmost importance. Here we consider several ion channels as examples to demonstrate that alignment of their 3D structures can significantly improve sequence alignment obtained by traditional methods.     

The diversity of mechanisms of the ion channels blockade as a way towards designing new pharmacological agents

Dysfunctions of glutamatergic synaptic neurotransmission often accompany various CNS disorders. Action of excessive glutamate, which causes excitotoxic effects by neuron depolarization and massive calcium influx can lead to cell death. Despite obvious importance of development of anti-glutamic neuroprotectors, among great number of known antagonists of ionotropic glutamate receptors only memantine is used in medicinal practice. One of the sources of numerous side effects caused by glutamate receptor antagonists is that the drugs usually inhibit receptors, which mediate both normal and pathological CNS processes. A possible approach to overcoming the problem is to develop the drugs whose action is enhanced in potentially pathological conditions such as high-frequency activation, high glutamate concentration, depolarized membrane, etc. Action of many classes of antagonists depends on pattern of receptor activation and on membrane voltage. In the present work, we discuss several peculiarities of channel blocking mechanisms from the viewpoint of neuroprotector development. In particular, we compare channel blockers which demonstrate different types of interaction with the channel gating machinery, we consider different types of voltage dependence and consider action of channel blockers, which can permeate through the channel. We conclude that meticulous analysis of the mechanism of action of the glutamate receptor channel antagonists could help to approach predicting of in vivo action using in vitro data.     

Planar aromaticity of <Emphasis Type="Italic">D</Emphasis><Subscript><Emphasis Type="Italic">N</Emphasis><Emphasis Type="Italic">h</Emphasis></Subscript>-symmetrical systems as a perturbed two-dimensional (2D) rigid rotor

Energy levels for D _{N h} -symmetrical cyclic polyenes with planar aromaticity were obtained using two-dimensional (2D) rigid rotor as the zeroth approximation. The addition of nuclei was simulated by the cosine-type potential and treated at the first-order perturbation theory. The result is qualitatively equivalent to that obtained using Hückel’s molecular orbital theory. As an addition, the energetic shift between σ and π orbitals is obtained using the model of electron oscillating around the center of a positively charged ring.     

Mitochondrial metabolism of guanine nucleotides. Possible role of guanosine

The catabolism of intramitochondrial guanine nucleotides was examined. During 30 min incubation of rat liver mitochondria at 37 degrees C in the presence of oligomycin and carboxyatractyloside, guanine and xanthine were formed and appeared in the medium. Under these conditions, the direct conversion of GMP to guanine by hypoxanthine-guanine phosphoribosyltransferase is suggested to be the main catabolic route within the organelles. Only very small amounts of guanosine were produced and detected both inside and outside the organelles. [14C]Guanosine and [14C]inosine were taken up by the mitochondria. Therefore, guanosine is suggested to be a precursor of intramitochondrial guanine nucleotides.