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At least 703 records · Page 39Linked to original sources
PubMed2005

Sodium, potassium-atpases in algae and oomycetes.

We have investigated the presence of K(+)-transporting ATPases that belong to the phylogenetic group of animal Na(+),K(+)-ATPases in the Pythium aphanidermatum Stramenopile oomycete, the Porphyra yezoensis red alga, and the Udotea petiolata green alga, by molecular cloning and expression in heterologous systems. PCR amplification and search in EST databases allowed one gene to be identified in each species that could encode ATPases of this type. Phylogenetic analysis of the sequences of these ATPases revealed that they cluster with ATPases of animal origin, and that the algal ATPases are closer to animal ATPases than the oomycete ATPase is. The P. yezoensis and P. aphanidermatum ATPases were functionally expressed in Saccharomyces cerevisiae and Escherichia coli alkali cation transport mutants. The aforementioned cloning and complementary searches in silicio for H(+)- and Na(+),K(+)-ATPases revealed a great diversity of strategies for plasma membrane energization in eukaryotic cells different from typical animal, plant, and fungal cells.

Amino Acid Sequence↗
PubMed2005

Contents of soluble, cell-wall-bound and exuded phlorotannins in the brown alga Fucus vesiculosus, with implications on their ecological functions.

Phlorotannins are ubiquitous secondary metabolites in brown algae that are phenotypically plastic and suggested to have multiple ecological roles. Traditionally, phlorotannins have been quantified as total soluble phlorotannins. Here, we modify a quantification procedure to measure, for the first time, the amount of cell-wall-bound phlorotannins. We also optimize the quantification of soluble phlorotannins. We use these methods to study the responses of soluble and cell-wall-bound phlorotannin to nutrient enrichment in growing and nongrowing parts of the brown alga Fucus vesiculosus. We also examine the effects of nutrient shortage and herbivory on the rate of phlorotannin exudation. Concentrations of cell-wall-bound phlorotannins were much lower than concentrations of soluble phlorotannins; we also found that nutrient treatment over a period of 41 days affected only soluble phlorotannins. Concentrations of each phlorotannin type correlated positively between growing and nongrowing parts of individual seaweeds. However, within nongrowing thalli, soluble and cell-wall-bound phlorotannins were negatively correlated, whereas within growing thalli there was no correlation. Phlorotannins were exuded from the thallus in all treatments. Herbivory increased exudation, while a lack of nutrients had no effect on exudation. Because the amount of cell-wall-bound phlorotannins is much smaller than the amount of soluble phlorotannins, the major function of phlorotannins appears to be a secondary one.

Animals↗
PubMed2004

Metabolic Flexibility of the Green Alga Chlamydomonas reinhardtii as Revealed by the Link between State Transitions and Cyclic Electron Flow.

In this Review we focus on the conversion of linear photosynthetic electron transport from water to NADP to the cyclic pathway around Photosystem I in the green alga Chlamydomonas reinhardtii. We discuss the strict relationship that exists between the changes in pathways of electron transport and state transitions, i.e., the reversible functional association of light harvesting proteins with one of the two photosystems of oxygenic photosynthesis. Such a link has not been reported in the case of other photosynthetic organisms, where the state transitions do not affect the pathway of electron transport. Rather, they provide a tool to optimise the rate of linear flow. We propose a kinetic-structural model that explains the mechanism of this particular relationship in Chlamydomonas, and discuss the advantages that this peculiar situation gives to the energetic metabolism of this alga.

Journal Article↗
PubMed2005

Chloroplast sulfate transport in green algae--genes, proteins and effects.

This review summarizes evidence at the molecular genetic, protein and regulatory levels concerning the existence and function of a putative ABC-type chloroplast envelope-localized sulfate transporter in the model unicellular green alga Chlamydomonas reinhardtii. From the four nuclear genes encoding this sulfate permease holocomplex, two are coding for chloroplast envelope-targeted transmembrane proteins (SulP and SulP2), a chloroplast stroma-targeted ATP-binding protein (Sabc) and a substrate (sulfate)-binding protein (Sbp) that is localized on the cytosolic side of the chloroplast envelope. The sulfate permease holocomplex is postulated to consist of a SulP-SulP2 chloroplast envelope transmembrane heterodimer, flanked by the Sabc and the Sbp proteins on the stroma side and the cytosolic side of the inner envelope, respectively. The mature SulP and SulP2 proteins contain seven transmembrane domains and one or two large hydrophilic loops, which are oriented toward the cytosol. The corresponding prokaryotic-origin genes (SulP and SulP2) probably migrated from the chloroplast to the nuclear genome during the evolution of Chlamydomonas reinhardtii. These genes, or any of its homologues, have not been retained in vascular plants, e.g. Arabidopsis thaliana, although they are encountered in the chloroplast genome of a liverwort (Marchantia polymorpha). The function of the SulP protein was probed in antisense transformants of C. reinhardtii having lower expression levels of the SulP gene. Results showed that cellular sulfate uptake capacity was lowered as a consequence of attenuated SulP gene expression in the cell, directly affecting rates of de novo protein biosynthesis in the chloroplast. The antisense transformants exhibited phenotypes of sulfate-deprived cells, displaying slow rates of light-saturated oxygen evolution, low levels of Rubisco in the chloroplast and low steady-state levels of the Photosystem II D1 reaction center protein. The role of the chloroplast sulfate transport in the uptake and assimilation of sulfate in Chlamydomonas reinhardtii is discussed along with its impact on the repair of Photosystem II from a frequently occurring photo-oxidative damage and H2-evolution related metabolism in this green alga.

Algal Proteins↗
PubMed1997

The fatty acid composition of a Vibrio alginolyticus associated with the alga Cladophora coelothrix. Identification of the novel 9-methyl-10-hexadecenoic acid.

The fatty acid composition of a new strain of Vibrio alginolyticus, found in the alga Cladophora coelothrix, was studied. Among 38 different fatty acids, a new fatty acid, 9-methyl-10-hexadecenoic acid and the unusual 11-methyl-12-octadecenoic acid, were identified. Linear alkylbenzene fatty acids, such as 10-phenyldecanoic acid, 12-phenyldodecanoic acid and 14-phenyltetradecanoic acid, were also found in V. alginolyticus. The alga contained 43% saturated fatty acids, and 28% C16-C20 polyunsaturated fatty acids of the n-3 and n-6 families.

Chlorophyta↗
PubMed1987

NADH:hydroxypyruvate reductase and NADPH:glyoxylate reductase in algae: partial purification and characterization from Chlamydomonas reinhardtii.

Hydroxypyruvate and glyoxylate reductase activities were measured in extracts from the unicellular green algae, Chlamydomonas reinhardtii, Chlorella vulgaris, Chlorella miniata, and Dunaliella tertiolecta. Only trace levels of these activities were detectable in the blue-green algae, Anabaena variabilis and Synechococcus leopoliensis. A NADH-dependent hydroxypyruvate reductase was purified 130-fold from Chlamydomonas to a specific activity of 18 mumol NADH oxidized X min-1 X mg protein-1. The pH optimum was 5.0 to 7.0 in the presence of phosphate and the Km(hydroxypyruvate) was 0.05 mM. Substrate inhibition by hydroxypyruvate could be partially relieved by phosphate. The molecular weight, estimated by gel filtration, was 96,000. NADH-dependent glyoxylate reductase activity copurified with the hydroxypyruvate reductase. The Km(glyoxylate) was 10 mM, and the pH optimum was 4.5 to 8.5. A specific NADPH:glyoxylate reductase was also partially purified which did not reduce hydroxypyruvate or pyruvate. The NADPH:glyoxylate reductase had a Km(glyoxylate) of 0.1 mM and a pH optimum of 5.0 to 9.5. These reductases were compared with the pyruvate reductase of Chlamydomonas which also catalyzes the reduction of both hydroxypyruvate and glyoxylate.

Alcohol Oxidoreductases↗
PubMed1992

Isolation and characterization of different forms of thioredoxins from the green alga Acetabularia mediterranea: identification of an NADP/thioredoxin system in the extrachloroplastic fraction.

A procedure has been developed for the simultaneous purification to apparent homogeneity of chloroplast thioredoxins f and m, and nonchloroplast thioredoxin h, from the green alga Acetabularia mediterranea. In the chloroplast fraction, three thioredoxins were isolated: one f type thioredoxin (Mr 13.4 kDa) and two m type thioredoxin forms (Mr of 12.9 and 13.8 kDa). A Western blot analysis of crude and purified chloroplast thioredoxin preparations revealed that Acetabularia thioredoxin m was immunologically related to its higher-plant counterparts whereas thioredoxin f was not. In the nonchloroplast fraction, a single form of thioredoxin h (Mr 13.4 kDa) and its associated enzyme NADP-thioredoxin reductase (NTR) were evidenced. Acetabularia NTR was partially purified and shown to be an holoenzyme composed of two 33.0-kDa subunits as is the case for other plant and bacterial NTRs. Similarity was confirmed by immunological tests: the algal enzyme was recognized by antibodies to spinach and Escherichia coli NTRs. Acetabularia thioredoxin h seemed to be more distant from higher-plant type h thioredoxins as recognition by antibodies to thioredoxin h from spinach and wheat was weak. The algal thioredoxin h was also slightly active with spinach and E. coli NTRs. These results suggest that in green algae as in the green tissues of higher plants the NADP and chloroplast thioredoxin systems are present simultaneously, and might play an important regulatory role in their respective cellular compartments.

Acetabularia↗
PubMed1975

Flash kinetics and light intensity dependence of oxygen evolution in the blue-green alga Anacystis nidulans.

Patterns of oxygen evolution in flashing light for the glue-green alga Anacystis nidulans are compared with those for broken spinach chloroplasts and whole cells of the green alga Chlorella pyrenoidosa. The oscillations of oxygen yield with flash number that occur in both Anacystis and Chlorella, display a greater degree of damping than do those of isolated spinach chloroplasts. The increase in damping results from a two- to threefold increase in the fraction (alpha) of reaction centers "missed" by a flash. The increase in alpha cannot be explained by non-saturing flash intensities or by the dark reduction of the oxidized intermediates formed by the flash. Anaerobic conditions markedly increase alpha in Anacystis and Chlorella but have no effect on alpha in broken spinach chloroplasts. The results signify that the mechanism of charge separation and water oxidation involved in all three orgainsms is the same, but that the pool of secondary electron acceptors between Photosystem II and Photosystem I is more reduced in the dark, in the algal cells, than in the isolated spinach chloroplasts. Oxygen evolution in flashing light for Anacystis and Chlorella show light saturation curves for the oxygen yield of the third flash (Y3) that differ markedly from those of the steady-state flashes(YS). In experiments in which all flashes are uniformly attenuated, Y3 requires nearly twice as much light as YS to reach half-saturation. Under these conditions Y3 has a sigmoidal dependence on intensity, while that of YS is hyperbolic. These differences depend on the number of flashes attenuated. When any one of the first three flashes is attenuated, the variation of Y3 with intensity resembles that of YS. When two of the first three flashes are attenuated, Y3 is intermediate in shape between the two extremes. A quantitative interpretation of these results based on the model of Kok et al. (Kik, B., Forbush, B.and McGloin, M. (1970) Photochem. Photobiol. 14, 307-321) fits the experimental data.

Chlorella↗
PubMed1977

The kinetic behavior of P-700 during the induction of photosynthesis in algae.

The kinetics of P-700 were examined spectrophotometrically during the induction of photosynthesis in algae. A pronounced oscillation was observed in the redox level of P-700 upon illumination of dark-adapted cells. The dark adaptation required approximately 1 min. The oscillation may be described as an initial rapid oxidation reaching a peak at approx. 50 ms followed by complete reduction of the pool of P-700. A subsequent slower oxidation resulted in attainment of the final state around 1 s. The main features of the oscillation were qualitatively the same in a wide variety of algae. The modulation in redox level of P-700 required high intensity activation of both photosystems and was eliminated by pre-illumination of the cells with weak short wavelength light but not by longer wavelengths absorbed primarily by Photosystem I. We propose that the P-700 modulation is directly related to the fast redox changes in Photosystem II which occur during the induction of photosynthesis. Cells incubated with methyl viologen did not show the P-700 oscillation confirming the suggestion previously advanced that exhaustion of Photosystem I acceptor and kinetic limitations in the carbon reduction cycle partially control the fast phase of photosynthetic induction.

Bacteria↗
PubMed1977

Temperature dependence on the delayed fluorescence of chlorophyll a in blue-green algae.

1. The delayed fluorescence of chlorophyll a was measured with a phosphoroscope by changing the temperature in a range of room temperatures in intact cells of blue-green algae, Anacystis nidulans, two strains of Anabaena variabilis and Plectonema boryanum, and other kinds of algae, Cyanidium caldarium and Chlorella pyrenoidosa. The induction of delayed fluorescence remarkably depended on the temperature of measurment. Nevertheless, the induction pattern was characterized by three levels of intensity; the initial rise level at the onset of excitation light, the maximum level after a period of excitation and the steady-state level after 10 min of excitation. 2. In A. nidulans and a strain of A. variabilis grown at various temperatures, close relationship was found between the phase transition of membrane lipids and the initial rise and the steady-state levels of delayed fluorescence. The initial rise level showed the maximum at the temperature of phase transition between the liquid crystalline and the mixed solid-liquid crystalline states, The steady-state levels showed a remarkable change from a high in the liquid crystalline state to a low level in the mixed solid-liquid crystalline state. 3. The millisecond decay kinetics of the delayed fluorescence measured at the steady-state level in A. nidulans grown at 38 degrees C consisted of two components with different decay rates. The half-decay time of the fast component was about 0.17 ms and was constant throughout the temperature range of measurement. The half decay time of slow component ranged from 0.6 to 1.5 ms, depending on the temperature of measurment.

Chlorella↗
PubMed1979

The electrophoretic isolation and partial characterization of three chlorophyll-protein complexes from blue-green algae.

Three chlorophyll-protein complexes have been resolved from blue-green algae using an improved procedure for membrane solubilization and electrophoretic fractionation. One complex has a red absorbance maximum of 676 nm and a molecular weight equivalency of 255 000 +/- 15 000. A second complex has an absorbance maximum of 676 nm, a molecular weight equivalency of 118 000 +/- 8000, and resembles the previously described P-700-chlorophyll a-protein (CPI) of higher plants and algae. The third chlorophyll-protein has a red absorbance maximum of 671 nm and a molecular weight equivalency of 58 000 +/- 5000. Blue-green algal membrane fractions enriched in Photosystem I and heterocyst cells do not contain this third chlorophyll-protein, whereas Photosystem II-enriched membrane fractions and vegetative cells do. A component of the same spectral characteristics and molecular weight equivalency was also observed in chlorophyll b-deficient mutants of barley and maize. It is hypothesized that this third complex is involved in some manner with Photosystem II.

Chlorophyll↗
PubMed1980

Isolation and characterization of soluble cytochrome c-553 and membrane-bound cytochrome f-553 from thylakoids of the green alga Scenedesmus acutus.

Soluble cytochrome c-553 and membrane-bound cytochrome f-553 from the alga Scenedesmus acutus were purified to apparent homogeneity. The properties of cytochrome c-553 are comparable to preparations obtained from other eukaryotic algae, whereas the thylakoid-bound species resembles higher plant cytochrome f. Common characteristics are: 1. An asymmetrical alpha-band at 553 nm. 2. A midpoint redox potential of +38 MV (pH 7.0), with a pH dependency above pH 8.0 of -60mV/pH unit. 3. Formation of a pyridine hemochromogen with a maximum at 550 nm; no adducts with CN- or CO are observed. Distinguishing features are: 1. Cytochrome f-553 has a more complicated beta-band, with maxima at 531.5 and 524 nm, and hence a more complex low-temperature spectrum. Also the positions of the gamma- and delta-bank at 421.5 and 331 nm, respectively, distinguish cytochrome f-553 from cytochrome c-553, with gamma- and delta-bands at 416 and 318 nm. 2. The ferricytochrome c-553 spectrum exhibits a weak band at 692 nm, which is not observed with cytochrome f.

Amino Acids↗
PubMed1980

Components and activity of the photosynthetic electron transport system of intact heterocysts isolated from the blue-green alga Nostoc muscorum.

Heterocysts of the blue-green alga Nostoc muscorum have been isolated by prolonged treatment with lysozyme. Quantitative data are presented which show the occurrence of cytochromes c-553, f-557 and b-563 in heterocysts in amounts comparable to vegetative cells. Particularly the content of the water-soluble cytochrome c-553 can be used to evaluate the intactness of a heterocyst preparation. Cytochrome f-557 has been partially purified and found to be a c-type cytochrome corresponding to cytochrome f of higher plants and other algae. Cytochrome b-559 is present in vegetative cells but not in heterocysts. The content of plastoquinone in heterocysts is reduced to 42% of the amount present in vegetative cells. These data suggest a degradation of Photosystem II during heterocyst differentiation. Measurements of photosynthetic electron transport in heterocysts proved the inability of the photosynthetic apparatus to carry out electron transport with electrons donated by water or diphenylcarbazide. In Tris-washed thylakoids from vegetative cells, however, diphenylcarbazide can act as an electron donor to Photosystem II.

Cyanobacteria↗
PubMed1981

Light-harvesting systems of brown algae and diatoms. Isolation and characterization of chlorophyll a/c and chlorophyll a/fucoxanthin pigment-protein complexes.

The present study examined the protein associations and energy transfer characteristics of chlorophyll c and fucoxanthin which are the major light-harvesting pigments in the brown and diatomaceous algae. It was demonstrated that sodium dodecyl sulfate (SDS)-solubilized photosynthetic membranes of these species when subjected to SDS polyacrylamide gel electrophoresis yielded three spectrally distinct pigment-protein complexes. The slowest migrating zone was identical to complex I, the SDS-altered form of the P-700 chlorophyll a-protein. The zone of intermediate mobility contained chlorophyll c and chlorophyll a in a molar ratio of 2 : 1, possessed no fucoxanthin, and showed efficient energy transfer from chlorophyll c to chlorophyll a. The fastest migrating pigment-protein zone contained fucoxanthin and chlorophyll a, possessed no chlorophyll c, and showed efficient energy transfer from fucoxanthin to chlorophyll a. It is demonstrated that the chlorophyll a/c-protein and the chlorophyll a/fucoxanthin-protein complexes are common to the brown algae and diatoms examined, and likely share similar roles in the photosynthetic units of these species.

Carotenoids↗
PubMed1994

Chlorophyll forms and excitation energy transfer pathways in light-harvesting chlorophyll a/b-protein complexes isolated from the siphonous green alga, Bryopsis maxima.

In this study, examination was made of chlorophyll (Chl) forms and energy transfer pathways in light-harvesting Chl a/b-protein complex (LHC II) isolated from the siphonous green alga, Bryopsis maxima. Three major Chl a forms (Ca664, Ca672 and Ca679) and one minor form (Ca688) were resolved at 15 degrees C. Two Chl b forms were resolved at 648 and 653 nm. Based on the number of Chl bound to an apoprotein, two Chls a were assigned to each of the three major Chl a forms, and three and five Chls b, to Cb648 and cb653, respectively. At 15 degrees C, fluorescence spectra were identical, irrespective of the excitation conditions of Chl a, Chl b and siphonaxanthin. Fluorescence from Chl b was detected in addition to that from all Chl a forms. Very efficient energy transfer from siphonaxanthin or Chl b to Chl a and even uphill transfer from Chl a to Chl b, were noted by measurement of the excitation spectra. At 15 degrees C, the equilibrium of energy distribution was established among pigments. However, Chl b was found not to mediate energy transfer from siphonaxanthin to Chl a. The partial amino acid sequence of Bryopsis LHC II was similar to those of green algae and higher plants. The energy transfer pathway between pigments and molecular organization of Bryopsis LHC II were compared with LHC II isolated from spinach.

Amino Acid Sequence↗
PubMed1988

First direct observation of the water exchange across the membrane of a single-cell green alga on a cellular level.

The isotopic water exchange across the membrane of a single-cell alga is made visible by optical differences of H2O and 2H2O. In the near infrared (NIR) (1000 to 2500 nm) H2O shows pronounced absorption bands while 2H2O is almost transparent. Results from in vivo experiments on the diffusive water permeation across the membrane of the spherical freshwater alga Eremosphaera viridis are presented. The evaluation of the isotope-exchange kinetics allows the calculation of the permeability coefficient, Pd, and the approximation of the intracellular diffusion constant, D. The extension of H2O/2H2O-exchange measurements to two dimensions opens new ways to study transport pathways up to the spatial resolution of a microscope. First NIR video images demonstrate the capability of the method.

Algorithms↗
PubMed1979

Ribulose 1,5-bisphosphate carboxylase from the thermophilic, acidophilic alga, Cyanidium caldarium (Geitler). Purification, characterisation and thermostability of the enzyme.

An an initial stage in the study of proteins from thermophilic algae, the enzyme ribulose 1,5-bisphosphate carboxylase 2-phospho-D-glycerate carboxylyase (dimerizing, EC 4.1.1.39) was purified 11-fold from the thermophilic alga Cyandium caldarium, with a 24% recovery. This purified enzyme appeared homogeneous on polyacrylamide gels and could be dissociated into two subunit types of molecular weights 55,000 and 14,900. The optimal assay temperature was 42.5 degrees C, whilst enzyme purified from Chlorella spp. showed maximum activity at 35 degrees C. The thermostability of Cyanidium ribulose 1,5-bisphosphate carboxylase was considerably greater than that of the Chlorella enzyme, and the presence of Mg2+ and HCO-3 further enhanced this heat stability. A break in the Arrhenius plot occured at 20 degrees C for Chlorella ribulose 1,5-bisphosphate carboxylase and 36 degrees C for the enzyme from Cyanidium. It is suggested that the thermostability of Cyanidium ribulose 1,5-bisphosphate carboxylase is a result of an inherent stability of the enzyme molecule which permits efficient CO2 fixation at high temperatures but results in low activity in the mesophilic temperature range.

Carboxy-Lyases↗
PubMed1984

Elucidation of fertilization and development in a red alga by quantitative DNA microspectrofluorometry.

Crucial nuclear events throughout the life histories of red algae have eluded researchers. Use of the DNA fluorochrome 4',6-diamidino-2-phenylindole (DAPI) and microspectrofluorometry has now resolved the problems. In the parasitic red alga Choreocolax polysiphoniae (= Leachiella pacifica), the amounts of nuclear DNA during the processes of meiosis and fertilization are documented as well as the transfer of the newly formed zygote nucleus to the adjacent accessory cell. In this organism, the G2 period predominates in the cell cycle of vegatative and reproductive cells; many nondividing vegetative cells become highly polyploid. The results indicate that the use of various fluorochromes combined with microspectrofluorometric measurements of individual nuclei is valuable for study of many developmental problems in lower eukaryotes where the relatively small nuclear DNA content has made study with conventional dyes impossible.

Cell Nucleus↗