RESUMO
Changes in the light energy distribution between the photosystems 1 and 2 (PS1 and PS2, respectively) due to the reversible migration of a part of the light-harvesting complex (LHC2) between the photosystems (state transitions, ST) have been studied in leaves of barley (Hordeum vulgare) and Arabidopsis thaliana plants upon short-term illumination with light of various intensity that excited predominantly PS2. Changes in the ratio of fluorescence maxima at 745 and 685 nm in the low-temperature (77 K) fluorescence spectrum of chlorophyll a (Chl a) characterizing energy absorption by the PS1 and PS2, respectively, were insufficient for revealing the differences in the STs in barley and Arabidopsis plants at various light intensities, because they were not associated with STs at high-intensity illumination. Light-induced accumulation of the LHC2 phosphorylated proteins Lhcb1 and Lhcb2 involved in the relocation of a part of the LHC2 from PS2 to PS1 in the leaves of both plants decreased with the increase in the light intensity and was more pronounced in barley than in Arabidopsis at the same light intensity. Relaxation of the non-photochemical quenching (NPQ) of Chl a fluorescence after illumination corresponding to the return of the part of LHC2 from PS1 to PS2 was observed in barley leaves in a wider range of increasing light intensities than in Arabidopsis leaves. The differences in the accumulation of phosphorylated Lhcb1 and Lhcb2, as well as in the parameters of NPQ relaxation after illumination, revealed that STs in barley leaves could occur not only at low-but also at high-intensity light, when it is absent in Arabidopsis leaves.
Assuntos
Arabidopsis/efeitos da radiação , Hordeum/efeitos da radiação , Complexos de Proteínas Captadores de Luz/efeitos da radiação , Luz , Iluminação , Fotossíntese/efeitos da radiação , Arabidopsis/metabolismo , Transferência de Energia/efeitos da radiação , Hordeum/metabolismo , Complexos de Proteínas Captadores de Luz/metabolismoRESUMO
The characteristics of the formation of the superoxide radical anion ([Formula: see text]) and hydrogen peroxide by xanthine oxidases isolated from microorganisms and from cow's milk were investigated. The increase in pH led to an increase in the rate of xanthine oxidation with oxygen by both xanthine oxidases. The functioning of xanthine oxidase from milk along with the two-electron reduction of O2 to H2O2 carries through the one-electron reduction of O2 to [Formula: see text], and the rate and the fraction of generation of [Formula: see text] increased with increasing pH. Under operation of the microbial xanthine oxidase, the [Formula: see text] radical was not detected in the medium. The results suggest a difference in the operation of active centers of enzyme from different sources.
Assuntos
Proteínas de Escherichia coli/química , Escherichia coli , Proteínas do Leite/química , Leite , Xantina Oxidase/química , Animais , Bovinos , Escherichia coli/enzimologia , Escherichia coli/isolamento & purificação , Leite/enzimologia , Leite/microbiologiaRESUMO
Changes in expression levels of genes encoding carbonic anhydrases α-CA1, α-CA2, α-CA4, ß-CA1, ß-CA2, ß-CA3, ß-CA4, ß-CA5, and ß-CA6 in Arabidopsis thaliana leaves after light increase from 80 to 400 µmol PAR quanta·m-2·s-1 were investigated under short day (8 h) and long day (16 h) photoperiods. The expression of two forms of the gene, At3g01500.2 and At3g01500.3, encoding the most abundant carbonic anhydrase of leaves, ß-CA1, situated in chloroplast stroma, was found. The content of At3g01500.3 transcripts was higher by approximately an order of magnitude compared to the content of At3g01500.2 transcripts. When plants were adapted to high light intensity under short day photoperiod, the expression level of both forms increased, whereas under long day photoperiod, the content of At3g01500.3 transcripts increased, and the content of transcripts of At3g01500.2 decreased. The expression levels of the At3g01500.3 gene and of genes encoding chloroplast carbonic anhydrases α-CA1, α-CA4, α-CA2 and cytoplasmic carbonic anhydrase ß-CA2 increased significantly in response to increase in light intensity under short day, and these of the first three genes increased under long day as well. The expression level of the gene encoding α-CA2 under long day photoperiod as well as of genes of chloroplast ß-CA5 and ß-CA4 from plasma membranes and mitochondrial ß-CA6 under both photoperiods depended insignificantly on light intensity. Hypotheses about the roles in higher plant metabolism of the studied carbonic anhydrases are discussed considering the effects of light intensity on expression levels of the correspondent genes.
Assuntos
Arabidopsis/metabolismo , Anidrases Carbônicas/genética , Regulação da Expressão Gênica de Plantas , Luz , Fotoperíodo , Arabidopsis/genética , Arabidopsis/efeitos da radiação , Anidrases Carbônicas/efeitos da radiação , Folhas de Planta/genética , Folhas de Planta/metabolismo , Folhas de Planta/efeitos da radiaçãoRESUMO
The expression of genes of two carbonic anhydrases (CA) belonging to the α-family, α-CA2 and α-CA4 (according to the nomenclature in N. Fabre et al. (2007) Plant Cell Environ., 30, 617-629), was studied in arabidopsis (Arabidopsis thaliana, var. Columbia) leaves. The expression of the At2g28210 gene coding α-CA2 decreased under increase in plant illumination, while the expression of the At4g20990 gene coding α-CA4 increased. Under conditions close to optimal for photosynthesis, in plants with gene At2g28210 knockout, the effective quantum yield of photosystem 2 and the light-induced accumulation of hydrogen peroxide in leaves were lower than in wild type plants, while the coefficient of non-photochemical quenching of leaf chlorophyll a fluorescence and the rate of CO2 assimilation in leaves were higher. In plants with At4g20990 gene knockout, the same characteristics changed in opposite ways relative to wild type. Possible mechanisms of the participation of α-CA2 and α-CA4 in photosynthetic reactions are discussed, taking into account that protons can be either consumed or released in the reactions they catalyze.
Assuntos
Proteínas de Arabidopsis/metabolismo , Arabidopsis/enzimologia , Anidrases Carbônicas/metabolismo , Ferredoxinas/metabolismo , Fotossíntese/fisiologia , Complexo de Proteína do Fotossistema II/metabolismo , Folhas de Planta/enzimologia , Arabidopsis/genética , Proteínas de Arabidopsis/genética , Anidrases Carbônicas/genética , Clorofila/genética , Clorofila/metabolismo , Clorofila A , Ferredoxinas/genética , Complexo de Proteína do Fotossistema II/genética , Folhas de Planta/genéticaRESUMO
This review presents information about carbonic anhydrases, enzymes catalyzing the reversible hydration of carbon dioxide in aqueous solutions. The families of carbonic anhydrases are described, and data concerning the presence of their representatives in organisms of different classes, and especially in the higher plants, are considered. Proven and hypothetical functions of carbonic anhydrases in living organisms are listed. Particular attention is given to those functions of the enzyme that are relevant to photosynthetic reactions. These functions in algae are briefly described. Data about probable functions of carbonic anhydrases in plasma membrane, mitochondria, and chloroplast stroma of higher plants are discussed. Update concerning carbonic anhydrases in chloroplast thylakoids of higher plants, i.e. their quantity and possible participation in photosynthetic reactions, is given in detail.
Assuntos
Anidrases Carbônicas/metabolismo , Plantas/enzimologia , Cloroplastos/enzimologia , FotossínteseRESUMO
Experimental data concerning the role of ascorbic acid in both the maintenance of photosynthesis and in the protection of the photosynthetic apparatus against reactive oxygen species and photoinhibition are reviewed. The function of ascorbic acid as an electron donor in the "Krasnovsky reaction", as well as its physiological role as a donor to components of the photosynthetic electron transport chain, which was first studied by A. A. Krasnovsky in the 1980s, is discussed. Data on the content and transport of ascorbic acid in plant cells and chloroplasts are presented.
Assuntos
Ácido Ascórbico/metabolismo , Fotossíntese/fisiologia , Ácido Ascórbico/química , Cloroplastos/metabolismo , Transporte de Elétrons , Complexo de Proteínas do Centro de Reação Fotossintética/química , Complexo de Proteínas do Centro de Reação Fotossintética/metabolismo , Proteínas de Plantas/química , Proteínas de Plantas/metabolismo , Plantas/metabolismo , Espécies Reativas de Oxigênio/química , Espécies Reativas de Oxigênio/metabolismoRESUMO
In arabidopsis plants, with an increase in illumination intensity during growth the extent of reduction of the plastoquinone pool in the photosynthetic electron transport chain increased, whereas the effective quantum yield of photosynthesis decreased. After 5 days of growth under high illumination intensity, these parameters in high light returned to values observed in "shade-adapted" plants in low light. During the same period, the size of the antenna decreased, correlating with a decrease in the amounts of proteins of peripheral pigment-protein complexes. It was found that the decrease in the amounts of these proteins occurred due to suppression of transcription of their genes.
Assuntos
Proteínas de Arabidopsis/metabolismo , Arabidopsis/metabolismo , Luz , Complexo de Proteína do Fotossistema II/metabolismo , Arabidopsis/crescimento & desenvolvimento , Proteínas de Arabidopsis/química , Transporte de Elétrons , Expressão Gênica , Oxirredução , Fotossíntese , Complexo de Proteína do Fotossistema II/química , Folhas de Planta/metabolismo , Plastoquinona/química , Plastoquinona/metabolismo , Teoria QuânticaRESUMO
The dye H(2)DCF-DA, which forms the fluorescent molecule DCF in the reaction with hydrogen peroxide, H(2)O(2), was used to study light-induced H(2)O(2) production in isolated intact chloroplasts and in protoplasts of mesophyll cells of Arabidopsis, pea, and maize. A technique to follow the kinetics of light-induced H(2)O(2) production in the photosynthesizing cells using this dye has been developed. Distribution of DCF fluorescence in these cells in the light has been investigated. It was found that for the first minutes of illumination the intensity of DCF fluorescence increases linearly after a small lag both in isolated chloroplasts and in chloroplasts inside protoplast. In protoplasts of Arabidopsis mutant vtc2-2 with disturbed biosynthesis of ascorbate, the rate of increase in DCF fluorescence intensity in chloroplasts was considerably higher than in protoplasts of the wild type plant. Illumination of protoplasts also led to an increase in DCF fluorescence intensity in mitochondria. Intensity of DCF fluorescence in chloroplasts increased much more rapidly than in cytoplasm. The cessation of cytoplasmic movement under illumination lowered the rate of DCF fluorescence intensity increase in chloroplasts and sharply accelerated it in the cytoplasm. It was revealed that in response to switching off the light, the intensity of fluorescence of both DCF and fluorescent dye FDA increases in the cytoplasm in the vicinity of chloroplasts, while it decreases in the chloroplasts; the opposite changes occur in response to switching on the light again. It was established that these phenomena are connected with proton transport from chloroplasts in the light. In the presence of nigericin, which prevents the establishment of transmembrane proton gradients, the level of DCF fluorescence in cytoplasm was higher and increased more rapidly than in the chloroplasts from the very beginning of illumination. These results imply the presence of H(2)O(2) export from chloroplasts to cytoplasm in photosynthesizing cells in the light; the increase in this export falls in the same time interval as does the cessation of cytoplasmic movement.
Assuntos
Cloroplastos/metabolismo , Peróxido de Hidrogênio/metabolismo , Luz , Plantas/metabolismo , Protoplastos/metabolismo , Antibacterianos/farmacologia , Arabidopsis/metabolismo , Proteínas de Arabidopsis/genética , Proteínas de Arabidopsis/metabolismo , Cloroplastos/efeitos dos fármacos , Fluoresceínas/química , Corantes Fluorescentes/química , Cinética , Nigericina/farmacologia , Pisum sativum/metabolismo , Fotossíntese , Folhas de Planta/metabolismo , Protoplastos/citologia , Protoplastos/efeitos dos fármacos , Spinacia oleracea/metabolismo , Zea mays/metabolismoRESUMO
The level of hormones in the tissues of sugar beet leaves of different age in parallel with their growth and metabolic activity was assayed; the latter was analyzed, measuring the contents of sugars and N-containing compounds, and the activities of Rubisco and proteases. The highest auxin and ABA concentration was detected in the actively growing upper leaf, while high level of cytokinins was maintained in the middle and upper leaves characterized by intensive photosynthesis. Leaf senescence being manifested in decline of chlorophyll content, decrease of photosynthesis and activation of proteolysis was accompanied by a decline in concentration of cytokinins. Glucose level gradually increased from upper (younger) to a lower (elder) leaves; this was accompanied with the signs of senescence on the background of decreased cytokinins level. Immuno-histochemical technique revealed increased level of abscisic acid in phloem parenchyma of the lowest leaf. The results suggest a possible involvement of auxins in maintaining leaf growth, an implication of decreased cytokinins level in the hypothesized induction of senescence by glucose, and a participation of abscisic acid in the active loading of metabolites into the phloem of senescing leaf.
Assuntos
Ácido Abscísico/metabolismo , Beta vulgaris/metabolismo , Clorofila/metabolismo , Fotossíntese/fisiologia , Reguladores de Crescimento de Plantas/metabolismo , Folhas de Planta/metabolismo , Regulação da Expressão Gênica de Plantas/fisiologiaRESUMO
Oxygen reduction in a photosynthetic electron-transport chain (PETC) was studied in isolated pea thylakoids in the presence of either ferredoxin, or ferredoxin + NADP+, or cytochrome c. The contribution of the electron flow through ferredoxin to the total oxygen reduction was evaluated by comparing the rate of oxygen reduction and the rate of oxidation of reduced ferredoxin in the light. It was found that at ferredoxin concentrations optimal for NADP+ reduction, 30-50% of electrons transferred to oxygen went through ferredoxin both in the absence and presence of NADP+. However, the absolute rate of oxygen reduction by membrane components of PETC in the presence of NADP+ was 3-4 times less than that in the presence of ferredoxin alone and close to the rate of oxygen reduction in the presence of cytochrome c. It was assumed that a Photosystem I component, whose role in this process depends on the rate of electron outflow from terminal acceptors of this photosystem, participates in oxygen reduction, and this component is phylloquinone.
Assuntos
Complexo de Proteínas da Cadeia de Transporte de Elétrons/metabolismo , Ferredoxinas/metabolismo , Oxigênio/metabolismo , Pisum sativum/metabolismo , Proteínas de Plantas/metabolismo , Tilacoides/metabolismo , Citocromos c/metabolismo , Transporte de Elétrons/fisiologia , NADP/metabolismo , Fotossíntese/fisiologia , Complexo de Proteína do Fotossistema I/metabolismo , Vitamina K 1/metabolismoRESUMO
The thylakoid membrane containing photosystem II (PSII membranes) from pea and wheat leaves catalyzed the reaction of CO2 hydration with low rate, which increased after their incubation either with Triton X-100, up to Triton/chlorophyll ratio 1:1, or 1 M CaCl2. The presence of the inhibitor of CAs, p-aminomethylbenzensulfonamide (mafenide), at the start line in the course of electrophoresis of PSII membranes solubilized by n-dodecyl-beta-maltoside (DM) decreased the amount of PSII core complex in the gel. The elution of PSII core complex from the column with immobilized mafenide occurred only either by mafenide or another inhibitor of CAs, ethoxyzolamide. The above results led to a conclusion that membrane-bound CA activity associated with PSII is situated in the core complex.
Assuntos
Anidrases Carbônicas/metabolismo , Complexo de Proteína do Fotossistema II/metabolismo , Plantas/enzimologia , Eletroforese em Gel de PoliacrilamidaRESUMO
Stimulation of the bicarbonate dehydration reaction in thylakoid suspension under conditions of saturating light at pH 7.6-8.0 was discovered. This effect was inhibited by nigericin or the lipophilic carbonic anhydrase (CA) inhibitor ethoxyzolamide (EZ), but not by the hydrophilic CA inhibitor, acetazolamide. It was shown that the action of EZ is not caused by an uncoupling effect. It was concluded that thylakoid CA is the enzyme utilizing the light-generated proton gradient across the thylakoid membrane thus facilitating the production of CO(2) from HCO(3)(-) and that this enzyme is covered from the stroma side of thylakoids by a lipid barrier.
Assuntos
Anidrases Carbônicas/metabolismo , Luz , Pisum sativum/citologia , Pisum sativum/enzimologia , Tilacoides/enzimologia , Acetazolamida/farmacologia , Bicarbonatos/metabolismo , Dióxido de Carbono/metabolismo , Inibidores da Anidrase Carbônica/farmacologia , Transporte de Elétrons/efeitos dos fármacos , Ativação Enzimática/efeitos dos fármacos , Etoxzolamida/farmacologia , Concentração de Íons de Hidrogênio , Membranas Intracelulares/efeitos dos fármacos , Membranas Intracelulares/enzimologia , Membranas Intracelulares/metabolismo , Cinética , Nigericina/farmacologia , Pisum sativum/metabolismo , Força Próton-Motriz/efeitos dos fármacos , Prótons , Tilacoides/efeitos dos fármacos , Tilacoides/metabolismo , DesacopladoresRESUMO
Oxygen uptake in isolated pea thylakoids in the presence of an inhibitor of plastoquinol oxidation by b (6)/f-complex dinitrophenylether of 2-iodo-4-nitrothymol (DNP-INT) was studied. The rate of oxygen uptake in the absence of DNP-INT had a distinct maximum at pH 5.0 followed by a decline to pH 6.5 and posterior slow rise, while in the presence of an inhibitor it increased at an increasing pH from 4.5 to 6.5 and then kept close to the rate in its absence up to pH 8.5. Gramicidin D substantially affected the oxygen uptake rate in the absence of DNP-INT, and only slightly in its presence. Such differences pointed to the presence of special oxygen reduction site(s) in photosynthetic electron transport chain 'before' cytochrome complex. Oxygen uptake in membrane fragments of Photosystem II (BBY-particles) was low and did not depend on pH. This did not support the participation of Q(B) in oxygen reduction in DNP-INT-treated thylakoids. Oxygen uptake in thylakoids in the presence of DNP-INT was inhibited by DCMU as well as by catalase in whole pH range. The catalase effect indicated that oxygen uptake was the result of dioxygen reduction by electrons derived from water, and that H(2)O(2) was a final product of this reduction. Photoreduction of Cyt c in the presence of DNP-INT was partly inhibited by superoxide dismutase (SOD), and this pointed to superoxide formation. The latter was confirmed by a rise of the oxygen uptake rate in the presence of ascorbate and by suppression of this rise by SOD. Both tests showed that the detectable superoxide radicals averaged 20-25% of potentially formed superoxide radicals the quantity of which was calculated from the oxygen uptake rate. The obtained data implies that the oxygen reduction takes place in a plastoquinone pool and occurs mainly inside the membrane, where superoxide can be consumed in concomitant reactions. A scheme for oxygen reduction in a plastoquinone pool in thylakoid membranes is proposed.
RESUMO
Evaluation of maize productivity under different climatic conditions was made by determination of the amount of the incident solar radiation energy in the PAR range, which can be potentially used by plants for photosynthesis. An irradiance, which can be stored in primary photosynthesis, designated as photosynthetic energy, W (ph), was estimated taking into account the action spectra of photosynthesis. Limitation of the W (ph) usage, owing to unfavorable environmental factors was considered. Quantitative evaluation of limitations by two such factors, air temperature and soil water potential, was made by means of the coefficients F(i), which were defined as the ratio between the photosynthetic rate at a given value of a particular environmental factor and that at the optimal value for this factor. The coefficients F(i), were determined from the dependencies of the photosynthesis rate on air temperature and soil water potential as obtained in chamber and field experiments. In general terms, the fraction of W (ph), which can be utilized under a given climatic condition, was named bioclimatic potential, W (pc). In our model, the effect of monodominancy, when strong action of one factor suppresses the influence of any other factor, was considered. In this case, the bioclimatic potential, designated W'(pc), was calculated by multiplying W (ph) times the coefficient F, for the factor which was most limiting during the period of measurement. There was close correlation between values of bioclimatic potential for the period of vegetation, W'(pc,v), and total dry matter. W'(pc,v) use efficiency in the maize crop was also evaluated for five variants of mineral nutrition.
RESUMO
Pea thylakoids with high carbonic anhydrase (CA) activity (average rates of 5000 micromol H(+) (mg Chl)(-1) h(-1) at pH 7.0) were prepared. Western blot analysis using antibodies raised against the soluble stromal beta-CA from spinach clearly showed that this activity is not a result of contamination of the thylakoids with the stromal CA but is derived from a thylakoid membrane-associated CA. Increase of the CA activity after partial membrane disintegration by detergent treatment, freezing or sonication implies the location of the CA in the thylakoid interior. Salt treatment of thylakoids demonstrated that while one part of the initial enzyme activity is easily soluble, the rest of it appears to be tightly associated with the membrane. CA activity being measured as HCO(3) (-) dehydration (dehydrase activity) in Photosystem II particles (BBY) was variable and usually low. The highest and most reproducible activities (approximately 2000 micromol H(+) (mg Chl)(-1) h(-1)) were observed in the presence of detergents (Triton X-100 or n-octyl-beta-D-glucopyranoside) in low concentrations. The dehydrase CA activity of BBY particles was more sensitive to the lipophilic CA inhibitor, ethoxyzolamide, than to the hydrophilic CA inhibitor, acetazolamide. CA activity was detected in PS II core complexes with average rate of 13,000 micromol H(+) (mg Chl)(-1) h(-1) which was comparable to CA activity in BBY particles normalized on a PS II reaction center basis.
RESUMO
The influence of quercetin on electron transport and photophosphorylation of pea isolated chloroplasts with methylviologen and NADP+ has been studied. Quercetin inhibits ATP synthesis and phosphorylating electron transport but does not affect the basal electron transport in the presence of methylviologen. In view of these data and because of the increase of the proton uptake by chloroplasts in the presence of quercetin we consider it as an inhibitor of energy transfer. Under conditions of NADP+ photoreduction quercetin acts also as an inhibitor of electron transfer, interacting with ferredoxin, though a complete inhibition of electron transfer has not been observed. This last phenomenon may be of importance for the understanding of the detailed mechanism of NADP+ reduction by chloroplasts.
Assuntos
Cloroplastos/metabolismo , Transporte de Elétrons/efeitos dos fármacos , Flavonoides/farmacologia , Fotofosforilação/efeitos dos fármacos , Quercetina/farmacologia , Depressão Química , Ferredoxinas/metabolismo , NADP/metabolismo , Oxirredução , Consumo de Oxigênio/efeitos dos fármacos , PrótonsRESUMO
The effects of magnesium ion concentration on the rate of electron transport in isolated pea thylakoids were investigated in the pH range from 4.0 up to 8.0. In the absence of magnesium ions in the medium and in the presence of 5 mM MgCl2 in the experiments not only without added artificial acceptors but also with ferricyanide or methylviologen as an acceptor, this rate had a well-expressed maximum at pH 5.0. It was shown that, after depression to minimal values at pH 5.5-6.5, it gradually rose with increasing pH. An increase in magnesium ion concentration up to 20 mM essentially affected the electron transfer rate: it decreased somewhat at pH 4.0-5.0 but increased at higher pH values. At this magnesium ion concentration, the maximum rate was at pH 6.0-6.5 and the minimum, at pH 7.0. Subsequent rise upon increasing pH to 8.0 was expressed more sharply. The influence of high magnesium ion concentration on the rate of electron transport was not observed in the presence of gramicidin D. It was found that without uncoupler, the changes in the electron transfer rate under the influence of magnesium ions correlated to the changes in the first-order rate constant of the proton efflux from thylakoids. It is supposed that the change in the ability of thylakoids to keep protons by the action of magnesium ions is the result of electrostatic interactions of these ions with the charges on the external surface of membranes. A possible role of regulation of the electron transport rate by magnesium ions in vivo is discussed.
Assuntos
Magnésio/farmacologia , Pisum sativum/metabolismo , Prótons , Tilacoides/metabolismo , Cátions Bivalentes , Transporte de Elétrons , Cloreto de Magnésio/farmacologiaRESUMO
The possible functions of a light-induced electron transfer to oxygen in the photosynthetic electron transport chain of higher plant chloroplasts are considered. The thermodynamic preconditions, as well as the experimental data about the participations of ferredoxin, the components of photosystems I and II, and plastoquinone in oxygen reduction are examined. It is concluded that, even in the presence of ferredoxin and ferredoxin + NADP+, oxygen reduction is carried out mainly by the membrane-bound carriers of the photosynthetic electron transport chain. The hypothesis is put forward that most superoxides, which are produced by reduction of O2 molecules by the intramembrane components of the acceptor side of photosystem I, are reduced within the membrane by the plastohydroquinone molecules to the hydrogen peroxide. It is assumed that the H2O2 molecules that originate as the result of this process serve for signaling about the redox state of the plastoquinone pool.
Assuntos
Cloroplastos/metabolismo , Oxigênio/metabolismo , Complexo de Proteína do Fotossistema I/metabolismo , Plastoquinona/metabolismo , Cloroplastos/enzimologia , Transporte de Elétrons , Ferredoxinas/metabolismo , Oxirredução , Tilacoides/metabolismoRESUMO
Carbonic anhydrase activities of pea thylakoids as well as thylakoid fragments enriched either in Photosystem 1 (PS1-membranes) or Photosystem 2 (PS2-membranes) were studied. The activity of PS1-membranes if calculated on chlorophyll basis was much higher than the activity of PS2-membranes. Acetazolamide, a non-permeable inhibitor of carbonic anhydrases, increased carbonic anhydrase activity of PS2-membranes at concentrations lower than 10(-6) M and suppressed this activity only at higher concentrations. A lipophilic inhibitor of carbonic anhydrases, ethoxyzolamide, effectively suppressed the carbonic anhydrase activity of PS2-membranes (I50 = 10(-9) M). Carbonic anhydrase activity of PS1-membranes was suppressed alike by both inhibitors (I50 = 10(-6) M). In the course of the electrophoresis of PS2-membranes treated with n-dodecyl-beta-maltoside "high-molecular-mass" carbonic anhydrase activity was revealed in the region corresponding to core-complex of this photosystem. Besides, carbonic anhydrase activity in the region of low-molecular-mass proteins was discovered in the course of such an electrophoresis of both PS2- and PS1-membranes. These low-molecular-mass carbonic anhydrases eluted from corresponding gels differed in sensitivity to specific carbonic anhydrase inhibitors just the same as PS1-membranes versus PS2-membranes. The results are considered as evidence for the presence in the thylakoid membranes of three carriers of carbonic anhydrase activity.