Biomedical subjects

A V Ruban

Publications and source records attributed to A V Ruban.

24 records · Page 2Linked to original sources

PubMed1996

Dynamic properties of the minor chlorophyll a/b binding proteins of photosystem II, an in vitro model for photoprotective energy dissipation in the photosynthetic membrane of green plants.

Excess light energy absorbed by the chloroplast membranes of green plants is dissipated by nonradiative de-excitation in order to protect against photodamage. This is observed as the nonphotochemical quenching of chlorophyll fluorescence, which has been suggested to result from an alteration in the structure and function of the chlorophyll a/b light-harvesting complexes of photosystem II (LHCII) due to the combined effects of protonation and the de-epoxidation of bound violaxanthin to form zeaxanthin. In agreement with this hypothesis, it is shown that the light-harvesting chlorophyll a/b proteins purified from spinach leaves exhibit pH-stimulated quenching of chlorophyll fluorescence; this quenching shares all the key features observed for the nonphotochemical quenching of chlorophyll fluorescence in vivo. In the case of the two minor complexes, LHCIIa (CP29) and LHCIIc (CP26), quenching is much greater than in the bulk complex LHCIIb and is strongly inhibited by the reagent dicyclohexylcarbodiimide. The carotenoids violaxanthin and zeaxanthin cause strong inhibition and stimulation of quenching, respectively, in these complexes. The results of this study are consistent with the suggestion that the minor light-harvesting complexes play a crucial role in photoprotective energy dissipation in the photosynthetic membrane of green plants. Moreover, for the first time, a system using isolated LHCIIa and LHCIIc for the study of the regulation of light harvesting is described.

Carotenoids↗

PubMed1995

Resonance Raman spectroscopy of the photosystem II light-harvesting complex of green plants: a comparison of trimeric and aggregated states.

Resonance Raman spectroscopy was performed on photosystem II light-harvesting complex (LHCII) in trimeric and oligomeric states with various excitation conditions. From these studies, it can be concluded that the structure of LHCII is altered during the trimer/oligomer transition. These structural changes affect the conformation of a population of carotenoid within the complex, which becomes twisted in the oligomeric form. Moreover, the interactions assumed by a chlorophyll a and a chlorophyll b are modified during the oligomerization process. This induces the formation of an H-bond to a formyl group of a chlorophyll b molecule and to a keto group of a chlorophyll a molecule. The extent to which these H-bonds to chlorophyll relate to the formation of the quencher cannot yet be precisely established. However, the structural changes they evidence may play a role in the control of the energy flux by LHCII complexes.

Carotenoids↗

PubMed1994

Higher plant light-harvesting complexes LHCIIa and LHCIIc are bound by dicyclohexylcarbodiimide during inhibition of energy dissipation.

We have investigated the binding to proteins of the photosynthetic apparatus of the carboxy-modifying agent dicyclohexylcarbodiimide, (cHxN)2C; this inhibits the protective dissipation of excess absorbed light energy (qE) by the light-harvesting apparatus of photosystem II (LHCII), suggesting that carboxyl amino-acid side chains within hydrophobic protein domains may be involved in qE. (cHxN)2(14)C was used to label thylakoids and photosystem II particles, so as to identify proteins which may be involved in the detection of lumen pH during qE induction. Of six thylakoid proteins labelled with (cHxN)2C under conditions where qE is efficiently induced, three are associated with photosystem I, and none with the bulk LHCII. PSII-associated label is bound to three minor components of LHCII, identified as LHCIIa (two species) and LHCIIc, as shown by protein sequencing of tryptic fragments of purified complexes. pH titration of qE formation and protein labelling in coupled thylakoids showed that both qE and labelling of LHCIIa increased at pH 7-8.

Amino Acid Sequence↗

PubMed1992

The molecular mechanism of the control of excitation energy dissipation in chloroplast membranes. Inhibition of delta pH-dependent quenching of chlorophyll fluorescence by dicyclohexylcarbodiimide.

Non-radiative dissipation of absorbed excitation energy in chloroplast membranes is induced in the presence of the trans-thylakoid proton motive force; this dissipation is measured as high energy state quenching of chlorophyll fluorescence, qE. It has been suggested that this results from a low pH-induced structural alteration in the light harvesting complex of photosystem II, LHCII [(1991) FEBS Letters 292, 1-4]. The effect of the carboxyl-modifying agent, dicyclohexylcarbodiimide (DCCD), on energy dissipation in chloroplast membranes has been investigated. At concentrations below that required to inhibit electron transport, DCCD caused a decrease in the steady state delta pH, completely inhibited qE and also inhibited the low pH-dependent induction of qE. DCCD binding to polypeptides in the 22-28 kDa range correlated with inhibition of qE. It is suggested that DCCD reacts with amino acid residues in LHCII whose protonation is the primary event in the induction of energy dissipation. This LHCII domain may be identical to one forming a proton channel linking the site of PSII-dependent water oxidation to the thylakoid lumen [(1990) Eur. J. Biochem. 193, 731-736].

Chlorophyll↗

PubMed1991

Control of the light-harvesting function of chloroplast membranes by aggregation of the LHCII chlorophyll-protein complex.

A new hypothesis is presented to explain the major molecular process that regulates the efficiency of light harvesting by chloroplast membranes. It is proposed that in excess light the decrease in the thylakoid lumen pH causes an increase in aggregation of the light harvesting complexes of photosystem II resulting in formation of an efficient pathway for non-radiative dissipation of excitation energy. The aggregation is potentiated by the conversion of violaxanthin to zeaxanthin. This hypothesis is based upon (i) similarity between the spectroscopic changes associated with energy dissipation and those observed upon aggregation of isolated light harvesting complex; and (ii) the link between changes in light scattering and increased energy dissipation.

Chlorophyll↗

PubMedDate not supplied

[A comparative evaluation of the efficacy of immunocorrection in children with bronchial asthma living in ecologically contrasted regions].

Overall 50 children suffering from infectious-allergic bronchial asthma who live in ecologically contrasting regions were examined. Those children residing in unfavourable, in terms of ecological conditions, regions demonstrated diminution of the peripheral blood T-lymphocytes together with a decrease in their functional activity as well as in the activity of interleukin 2. It is in this group of children that immunomodulating effect of thymalin is less apparent. It is suggested that the relevant immune correction in such cases might be achieved through repeated courses of treatment with immunomodulating agents and rehabilitation of patients in favourable ecological conditions together with prescribing of other immunostimulators of selective action in respect of the T-link of the immunity system.

Adjuvants, Immunologic↗