Nitrogen fixation and heterocysts in the blue-green alga Anabaena cylindrica

The site of nitrogen fixation in the blue-green alga Anabaenacylindrica Lemra (Fogg strain) was investigated. Less than 4%of the total nitrogen fixed during a relatively short period(5-15 min) was recovered in heterocysts. When estimated on thecellular nitrogen basis, vegetative cells can fix molecularnitrogen at the same rate as do heterocysts. There was no positivecorrelation between nitrogen fixation and heterocyst formation.Results do not support the hypothesis that the heterocyst isthe main site for nitrogen fixation in blue-green algae. ¹ This work was supported by grant (No. 38814) from the Ministryof Education. (Received July 23, 1971; )     

Photophosphorylation in isolated heterocysts from the blue-green alga Nostoc muscorum

Isolated heterocysts of the blue-green alga Nostoc muscorum (Anabaena 7119) exhibit high rates of photophosphorylation in systems with cyclic and non-cyclic electron transport. Cyclic photophosphorylation mediated by N-methylphenazonium methosulfate is found to be sensitive to antimycin A, but not to 2,5-dibromo-3-methyl-6-isopropyl-p-benzoquinon (DBMIB). Non-cyclic electron transport (diaminodurol → methylviologen) coupled to phosphorylation is affected by DBMIB, but not by antimycin A. Studies with uncouplers indicate that ΔpH is the main component of the protonmotive force under continuous illumination. A different effect of NH₄Cl on dark- and photophosphorylation is observed and discussed with respect to localization of respiration in blue-green algae.     

Activities of enzymes of the oxidative and the reductive pentose phosphate pathways in heterocysts of a blue-green alga

Preparations of heterocysts of Anabaena cylindrica Lemm. had 7- to 8-fold higher activities of glucose 6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase, 2-fold more hexokinase activity, and 0.02 to 0.06 times as much ribulose diphosphate carboxylase and glyceraldehyde 3-phosphate dehydrogenase activities as did whole filaments per milligram soluble protein in cell-free extracts. Time courses of solubilization of glucose 6-phosphate dehydrogenase activity indicated that heterocysts contain 74 to 80% of the total activity of this enzyme in filaments.     

Particle aggregation in photosynthetic membranes of the blue-green alga Anacystis nidulans

Freeze-fracture electron microscopy demonstrates that in photosynthetic membranes of the blue-green alga Anacystis nidulans quenched from a temperature below growth temperature, areas devoid of membrane particles occur. We suggest that this phenomenon is related to phase transitions in the photosynthetic membrane.     

Particle aggregation in photosynthetic membranes of the blue-green alga Anacystis nidulans.

Freeze-fracture electron microscopy demonstrates that in photosynthetic membranes of the blue-green alga Anacystis nidulans quenched from a temperature below growth temperature, areas devoid of membrane particles occur. We suggest that this phenomenon is related to phase transitions in the photosynthetic membrane.     

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.     

Identification and analysis of a lipopolysaccharide in cell walls of the blue-green alga Anacystis nidulans

Summary A lipopolysaccharide was isolated from cell walls of Anacystis nidulans by extraction with 45% aqueous phenol at 65°, and further purified by repeated high speed centrifugation. It contains 30–40% of lipid and about 60% of carbohydrate components. The carbohydrate moiety contains predominantly mannose and smaller amounts of galactose, glucose, fucose, rhamnose, 2-keto-3-deoxyoctonate, glucosamine and a second aminosugar. The latter was identified as a 2-amino-2-deoxyheptose with the gluco-configuration from C3 to C7. Thelipid moiety contains glucosamine and fatty acids (C22:0, C18:2, C16:0, C12:0 and C14:OH). The lipopolysaccharide has a very low phosphate content and does not contain heptose. It shows low pyrogenicity in rabbits and it is not toxic in mice.Abbreviations KDO 2-Keto-3-deoxy-octonate - LPS Lipopolysaccharide     

Characterization of the protein from gas-vacuole membranes of the blue-green alga,Microcystis aeruginosa

Summary The purified protein which constitutes the membranes of the gas vacuoles of the the blue-green alga, Microcystis aeruginosa, was partially characterized. Gel electrophoresis and end-group analysis indicate that the protein is a single species. Strongly protic solvents such as formic acid are the only reagents causing appreciable solubilization of the membrane protein. Infrared spectroscopy shows that the membrane protein has both -helix or random-coil conformation, and -conformation.This work was supported by the U. S. Atomic Energy Commission under Contract AT-(11-1)-1338.     

Photosynthetic activities of a thermophilic blue-green alga

Photosynthetic activities of a thermophilic blue-green alga,a species of Synechococcus, were studied with special referenceto its growth at high temperatures. A rapid algal growth occurredin the temperature range between 50 and 60?C, showing the maximumrate, six doublings per day, at about 57?C. Photosynthetic oxygenevolution and methyl viologen photoreduction in the cells werealso active at high temperatures and the optimum temperaturesfor these activities agreed with that of the algal growth. Thegrowth and photosynthetic activities were very low at room temperatureand irreversibly inactivated at temperatures above 60?C. The thylakoid membranes isolated from the alga were also photochemicallyactive at high temperatures. The membranes mediated ferricyanidephotoreduction coupled with a stoichiometric oxygen evolutionat a rate comparable to that of photosynthetic oxygen evolutionin the cells. The optimum temperature for the reaction was ashigh as 50?C. The membranes also showed a photosystem I-mediatedreaction at high temperatures. These observations indicate thatthe thylakoid membranes are intrinsically thermophilic in thisorganism. Thus the growth of the alga at high temperatures canbe well correlated to thermophilic properties of the photosyntheticapparatus. (Received February 20, 1978; )     

Structures in a blue-green alga resembling prolamellar bodies

Summary Cells ofAnabaena (IUCC 380) from soil-water cultures 106 and 168 days after inoculation were fixed in 2% KMnO₄ and studied by electron microscopy. Thylakoid lattices morphologically similar to prolamellar bodies characteristic of etiolated higher plant chloroplasts were discovered. Prefixation sonication and centrifugation were eliminated as factors producing these lattices in the photosynthetic thylakoid system of these prokaryotic cells. Similar lattices are not seen in young cultures in the log phase of growth cultured under the same temperature and light conditions in the same medium. Factors, other than age, producing these lattices are yet to be determined.     

Energy transduction in the photosynthetic membranes of the cyanobacterium (blue-green alga) P-lectonema boryanum.

Membrane preparations isolated from the photosynthetic lamellae of the cyanobacterium Plectonema boryanum generate upon illumination a transmembrane pH gradient of approximately 2 to 3 pH units (acid inside), as determined from the distribution of either fluorescent or radioactive amines (9 aminoacridine and [14C]methylamine, respectively). Using the distribution of permeant ions to measure the electrical potential across the membrane, it was found that the latter is practically nil under conditions in which the deltapH is formed and photophosphorylation takes place. In agreement with the above findings cyclic photophosphorylation in this membrane preparation is inhibited by agents shown to collapse the deltapH but not by agents which should collapse the electrical potential. It is deduced that the pattern of proton movement in the photosynthetic lamellae of intact Plectonema spheroplasts corresponds to that of the cell-free membrane system, as both preparations show similar light dependent accumulation of fluorescent amine. It is concluded that the pattern of energy transduction in Plectonema photosynthetic lamellae is similar to that of chloroplast thylakoid membranes and not to that of bacterial cytoplasmic membranes. The evolutionary implications of the findings are discussed and a model for the directionality of H+ movements in the whole cell is presented.     

Phycobilisomes from a blue-green alga Nostoc species

Phycobilisomes were isolated from a Nostoc sp. strain Mac in phosphate buffer (pH 7.0) by treatment with 1% Brij 56 and centrifugation on discontinuous sucrose gradients (2.0, 1.0, 0.5, and 0.25 M in the proportions 6:4:4:10 ml, respectively). Absorption spectra of isolated phycobilisomes showed the presence of phycoerythrin, phycocyanin, and allophycocyanin. The phycobilisome pigments were partially resolved by electrophoresis on acrylamide gels. Stained gels demonstrated that each main protein band corresponded to a pigmented region. The phycobilisomes appeared compact with a rounded surface and flattened base (about 40-nm diameter) at the attachment site to the photosynthetic lamellae. Fixation in glutaraldehyde caused a significant reduction in total pigment absorption, as well as shifts in the absorption maxima, particularly that of phycoerythrin.     

Photosynthetic electron transport and phosphorylation reactions in thylakoid membranes from the blue-green alga Anacystis nidulans.

Thylakoid membranes were prepared from the blue-green alga, Anacystis nidulans with lysozyme treatment and a short period of sonic oscillation. The thylakoid membrane preparation was highly active in the electron transport reactions such as the Hill reactions with ferricyanide and with 2,6-dichlorophenolindophenol, the Mehler reaction mediated by methyl viologen and the system 1 reaction with methyl viologen as an electron acceptor and 2,6-dichlorophenolindophenol and ascorbate as an electron donor system. The Hill reaction with ferricyanide and the system 1 reaction was stimulated by the phosphorylating conditions. The cyclic and non-cyclic phosphorylation was also active. These findings suggest that the preparation of thylakoid membranes retained the electron transport system from H2O to reaction center 1, and that the phosphorylation reaction was coupled to the Hill reaction and the system 1 reaction.     

Intracellular localization of glycolate dehydrogenase in a blue-green alga

Glycolate dehydrogenase activity was detected in cell-free extracts of Oscillatoria sp. prepared by osmotic lysis of spheroplasts in 0.05 m potassium phosphate buffer, pH 7.5, containing 0.3 m mannitol. Most of the enzyme activity was found in a particulate fraction and localized in the photosynthetic lamellae after centrifugation in a discontinuous sucrose density gradient. Enzyme activity was detected in this fraction both in the presence and absence of the artificial electron acceptor 2,6-dichlorophenolindophenol (DPIP) and a low rate of O(2) uptake was detected in this lamellar fraction. Activity was lost from the lamellar fraction by repeated washing or by treatment with 0.005% Triton X-100 and the solubilized enzyme activity was DPIP-dependent. The data indicate that both glycolate dehydrogenase and its natural electron acceptor are bound to the photosynthetic lamellae in vivo. In contrast, catalase activity was found in the soluble cytoplasmic fraction.     

Lipids as organizers of cell membranes

The 105th Boehringer Ingelheim Fonds International Titisee Conference 'Lipids as Organizers of Cell Membranes' took place in March 2012, in Germany. Kai Simons and Gisou Van der Goot gathered cell biologists and biophysicists to discuss the interplay between lipids and proteins in biological membranes, with an emphasis on how technological advances could help fill the gap in our understanding of the lipid part of the membrane.     

Temperature dependence of the photosynthetic activities in the thylakoid membranes from the blue-green alga Anacystis nidulans.

The effects of temperature and ethidium bromide on the banding of heat-denatured DNA was studied during equilibrium centrifugation in density gradients of NaI. Centrifugation at 10 degrees C prevents the partial renaturation of Escherichia coli DNA and Clostridium perfringens DNA that occurs at 20 degrees C. A centrifugation temperature of --5 degrees C is required to prevent renaturation of T7 phage DNA. Ethidium bromide decreases renaturation of Escherichia coli DNA during centrifugation at 20 degrees C and causes a small shift in the buoyant density of both denatured and native DNA. Equilibrium centrifugation at lower temperatures prevents DNA renaturation and permits increased utilization of the large buoyant density difference between native and heat-denatured DNA in gradients of NaI.