Photosystem I-dependent oxidation of organic acids in blue-green alga, Anabaena variabilis

Photosynthetic lamellar fragments isolated from photoautotrophicallygrown cells of Anabaena variabilis were tested for their methylviologen photoreduction activity by coupled oxygen uptake inthe presence of CMU. Four kinds of organic acids, glycolate,malate, succinate and isocitrate, were found to serve as electrondonors of photosystem I, bypassing photosystem II, as in thecase of reduced DCPIP. Spectrophotometric measurement revealedthat the dark reduction of photooxidized cytochrome f and P700was markedly accelerated if one of the four organic acids waspresent. (Received April 18, 1975; )     

Ribosomes from the blue-green alga Anabaena variabilis

Summary Extracts from the blue-green alga Anabaena variabilis were prepared by ultrasonic disintegration or by extrusion through a French pressure cell; examination by sucrose density gradient centrifugation and analytical ultracentrifugation indicated the existence of a procaryotic (70S) ribosome. However both the ribosomes and their sub-units were found to be relatively unstable after isolation and examination in tris buffer pH 7.4 but not in 10^-3 m-sodium phosphate buffer pH 7.0 containing 10^-1 m-potassium chloride. Experiments with ³²P and ³⁵S isotopes indicated that this instability was associated with the loss of ³⁵S labelled material, presumably therefore protein rather than nucleic acid. A comparison of behaviour with that of bacterial ribosomes is presented and the existence of certain similarities to ribosome preparations from chloroplasts of several plant species discussed.     

Photoorganotrophic growth of a blue-green alga, Anabaena variabilis

By training Anabaena variabilis in the presence of glucose andcasamino acids, the cells became proliferable without a supplyof CO₂. Their growth under these conditions was not affectedby CMU and their growth rates were linearly proportional tothe light intensity, inferring that this growth was independentof photosystem II action and its nutritional mode was of photoorganotrophicnature. The process of transition to this nutritional mode includedat least two consecutive stages: relief from the susceptibilityto organic substances which initially evoked arrest of cellgrowth, followed by the shift of cellular metabolism to organotrophy.In cells grown photoorganotrophically, the contents of phycobilinpigments decreased to nearly one-fifth as much as that of lithotrophicallygrown cells with concomitant degradation of the activity ofphotosynthetic oxygen evolution, while the chlorophyll contentsremained less altered. Accompanying these results, the activityfor incorporating external amino acids into cellular proteinswas enhanced several hundred times. Neither in the dark norin anaerobiosis was this organotrophic growth permitted butwhen light too dim to support lithotrophic growth was supplied,the organotrophic growth was affected at a slow but discerniblerate. (Received August 2, 1974; )     

Die-offs of the blue-green alga,Anabaena variabilis,in fish ponds

Dense populations of the blue-green alga, Anabaena variabilis, frequently develop in fish ponds at Auburn, Alabama, during windy weather in March and early April. Massive die-offs of this alga can be expected when it forms surface scums during prolonged periods of calm, clear, warm weather between mid April and mid May. Dissolved oxygen concentrations decline following die-offs and fish kills may result.     

Lipopolysaccharide containing L-acofriose in the filamentous blue-green alga Anabaena variabilis

For the first time, an O-antigenic lipopolysaccharide (LPS) has been isolated from a filamentous blue-green alga (Anabaena variabilis). It was extractable with phenol-water, resulting in extraction of the bulk of the LPS into the phenol phase. The polysaccharide moiety of this LPS consists of l-rhamnose, its 3-O-methyl ether l-acofriose, d-mannose, d-glucose, and d-galactose. l-Glycero-d-mannoheptose and 2-keto-3-deoxyoctonate, the two characteristic sugar components of enteric LPS, and phosphate groups are absent from the A. variabilis O antigen. The only amino sugar present is d-glucosamine. Three hydroxy fatty acids were identified, namely, beta-hydroxymyristic, beta-hydroxypalmitic and beta-hydroxystearic acids, in addition to palmitic and unidentified fatty acid. The LPS of A. variabilis is localized in the outermost cell wall layer and behaves like a bacterial O antigen in serological tests. The passive hemagglutination yielded high titers with isolated LPS (pretreated by heat or by alkali) and rabbit antisera prepared against living or heat-killed cells. The position of the precipitation arcs after immunoelectrophoresis of the O antigen indicates the lack of charged groups. The water phase of the phenol-water extract contains, in high yield, a glucose polymer. It is serologically inactive as shown by the passive hemagglutination test and by agar-gel precipitation.     

Estimation of chlorophyll a distribution in the photosynthetic pigment systems I and II of the blue-green alga Anabaena variabilis.

Chlorophyll a distribution in pigment systems I and II was estimated with the blue-green alga Anabaena variabilis by two methods: first, with intact cells using delayed light emission as an index reaction; second, by measuring the 2,6-dichlorophenolindophenol-Hill reaction and the cytochrome c photooxidation in membrane fragments. The first estimation indicated that 0.053+/-0.014 of total chlorophyll a functions as a component of pigment system II, and the second method 0.086+/-0.012. Though the values were somewhat different in the two methods, both estimations indicated that pigment system II chlorophyll a occupies a very small fraction of total chlorophyll a.     

Intracellular ATP level and light-induced inhibition of respiration in a blue-green alga, Anabaena variabilis

To evaluate the possibility that the respiration of photosyntheticorganisms competes with photophosphorylation for ADP in vivo,we determined the intracellular ATP level in cells of Anabaenavariabilis under various respiratory conditions; maintainedin darkness, light-inhibited or uncoupled. No substantial differencein ATP level was observed between the light-inhibited and dark-keptcells. Under dark anaerobic conditions, however, the ATP leveldecreased to nearly one-third that of the aerobic level, indicatinga capacity for oxidative phosphorylation in this alga. In thepresence of 10^–5 M CCCP, the ATP level was reduced toabout half that of the control, but the light-inhibited respirationwas not eliminated by this agent, suggesting that it is notdue to the decreased ADP level. A possible mechanism for thephotoinhibition is discussed with special reference to the procaryoticintracellular structure of this alga. (Received October 24, 1975; )     

Association of NAD and NADP linked glyceraldehyde-3-phosphate dehydrogenase in the blue-green alga,Anabaena variabilis

Summary Gel-filtration of glyceraldehyde-3-phosphate dehydrogenase from Anabaena variabilis indicates a mol. wt. of 200,000–300,000, which is significantly greater than previously reported for this enzyme from other sources. Reaction rates in the presence NAD of and NADP suggest that one enzyme only is operative, being active with either coenzyme at any one time. Centrifugation and electrophoretic studies support this conclusion. The possible consequences of these results in the control of intermediary metabolism are discussed.     

X-ray diffraction studies on photosystem I fragments from a blue-green alga, Anabaena variabilis, and spinach

Photosystem I fragments were prepared from thylakoid membranes of a blue-green alga (Anabaena variabilis) and spinach by treatment with a detergent, Triton X-100. Equatorial X-ray diffraction patterns were recorded on films for oriented specimens of thylakoid membranes and photosystem I fragments. The thylakoid membranes and photosystem I fragments gave essentially the same equatorial diffraction patterns in both Anabaena variabilis and spinach, indicating that the major X-ray scatterers in these thylakoid membranes are the molecular assembly of photosystem I. The equatorial X-ray diffraction from the photosystem I fragments of Anabaena variabilis and spinach extends to the reciprocal space of 1/7 A-1. The diffraction pattern exhibits six to nine distinct maxima though they are diffuse, indicating that the arrangement of the constituent molecules in photosystem I has a definite geometrical regularity. The radial autocorrelation functions indicate that the maximal sizes of photosystem I in these thylakoid membranes are about 100 A, and the geometrical regularity does not correspond to a crystalline order. The X-ray diffraction patterns from photosystem I fragments from Anabaena variabilis and spinach are quite similar to each other, suggesting the possibility that the molecular structures of photosystem I in Anabaena variabilis and spinach have a fundamental similarity. These diffraction patterns, however, are different from that of the chromatophore obtained from a photosynthetic bacterium, Rhodospirillum rubrum.     

The utilization of molecular hydrogen by the blue-green alga Anabaena cylindrica

The blue-green alga Anabaena cylindrica is found to consume molecular hydrogen in a hydrogenase dependent reaction. This hydrogen uptake proceeds in the dark and is strictly dependent on oxygen, thus representing a Knallgas reactions. Its rate is almost as high as that of the endogenous respiration in Anabaena. Studies with inhibitors reveal that hydrogen is utilized via the complete respiratory chain providing additional energy for the alga. CO plus C₂H₂ completely block the Knallgas reaction which explains the previously reported considerable increase in the total H₂ formation representing the difference between the nitrogenase-dependent H₂-evolution and the reutilization of the gas catalysed by the hydrogenase in intact Anabaena.H₂ is able to support the C₂H₂-reduction in the dark in a reaction again strictly dependent on oxygen. Moreover, H₂ is also consumed in experiments carried out under far red light and in the presence of dichlorophenyl-dimenthyl-urea (DCMU) where the energy for nitrogen fixation is no longer provided by respiration but by cyclic photophosphorylation. Under these conditions, H₂ is found to supply electrons for the formation of C₂H₄ from C₂H₂ in a reaction no longer dependent on the presence of oxygen. Moreover, in these experiments, the presence of H₂ stabilizes the C₂H₂-reduction activity against the deleterious effect of oxygen.Thus, this communication provides evidence for a triplicate function of the H₂-uptake catalysed by hydrogenase in intact Anabaena which is (a) to provide energy by the Knallgas reaction, (b) to supply reducing equivalents for nitrogenase, (c) to protect nitrogenase from damage by oxygen.Abbreviations DCMU N-(3,4-dichlorophenyl)N,N-dimethylurea - DNP 2-4-dinitrophenol - FCCP carbonylcyanid-p-trifluormethoxyphenyl-hydrazone(=p-CF₃-CCP) - Chl chlorophyll