Internal conversion in the photosynthetic mechanism of blue-green algae

1. In Chroococcus a quantum of light absorbed by phycocyanin has 90 per cent the chance of doing photosynthesis that a quantum absorbed by chlorophyll has. 2. By a process analogous to internal conversion in radioactivity (but with the linear dimensions and the wave length 10⁴ times larger) there will be transferred from phycocyanin to chlorophyll See PDF for Equation (a number of the order of 100) quanta for every one emitted as fluorescent light by the phycocyanin in the Chroococcus cell. 3. The yield of fluorescent light in Chroococcus is between 1 and 2 per cent. 4. The transfer of energy by internal conversion can account for the photosynthesis by phycocyanin observed by Emerson and Lewis.     

Relation between pigment content and photosynthetic characteristics in a blue-green algae

1. The blue-green alga Anacystis nidulans was cultured under steady state conditions at 25 and 39°C. and under several different light intensities to give five different types of cells. 2. Cells were submitted to pigment analysis based upon acetone extracts and aqueous extracts obtained by sonic disintegration. The different cell types show a threefold range of chlorophyll content and a fourfold range of phycocyanin content with only minor changes in the chlorophyll/phycocyanin ratio. Cells of highest pigment content were estimated to contain 2.8 per cent chlorophyll a and 24 per cent phycocyanin, the latter on a total chromoproteid basis. 3. Light intensity curves of photosynthesis were obtained for each of the cell types at 25 and at 39°C. The slopes of the light-limited regions of the curves are approximately linear functions of chlorophyll and phycocyanin contents. Maximum light-saturated rates of photosynthesis at 25 and 39° show no simple relation to pigment content.     

Mechanism of light induced water splitting in Photosystem II of oxygen evolving photosynthetic organisms

The reactions of light induced oxidative water splitting were analyzed within the framework of the empirical rate constant-distance relationship of non-adiabatic electron transfer in biological systems (C. C. Page, C. C. Moser, X. Chen , P. L. Dutton, Nature 402 (1999) 47-52) on the basis of structure information on Photosystem II (PS II) (A. Guskov, A. Gabdulkhakov, M. Broser, C. Gl?ckner, J. Hellmich, J. Kern, J. Frank, W. Saenger, A. Zouni, Chem. Phys. Chem. 11 (2010) 1160-1171, Y. Umena, K. Kawakami, J-R Shen, N. Kamiya, Crystal structure of oxygen-evolving photosystem II at a resolution of 1.9?. Nature 47 (2011) 55-60). Comparison of these results with experimental data leads to the following conclusions: 1) The oxidation of tyrosine Y(z) by the cation radical P680(+·) in systems with an intact water oxidizing complex (WOC) is kinetically limited by the non-adiabatic electron transfer step and the extent of this reaction is thermodynamically determined by relaxation processes in the environment including rearrangements of hydrogen bond network(s). In marked contrast, all Y(z)(ox) induced oxidation steps in the WOC up to redox state S(3) are kinetically limited by trigger reactions which are slower by orders of magnitude than the rates calculated for non-adiabatic electron transfer. 3) The overall rate of the triggered reaction sequence of Y(z)(ox) reduction by the WOC in redox state S(3) eventually leading to formation and release of O(2) is kinetically limited by an uphill electron transfer step. Alternative models are discussed for this reaction. The protein matrix of the WOC and bound water molecules provide an optimized dynamic landscape of hydrogen bonded protons for catalyzing oxidative water splitting energetically driven by light induced formation of the cation radical P680(+·). In this way the PS II core acts as a molecular machine formed during a long evolutionary process. This article is part of a Special Issue entitled: Photosynthesis Research for Sustainability: from Natural to Artificial.     

Feedback regulation of arginine biosynthesis in blue-green algae and photosynthetic bacteria

Hoare, D. S. (The University of Texas, Austin), and S. L. Hoare. Feedback regulation of arginine biosynthesis in blue-green algae and photosynthetic bacteria. J. Bacteriol. 92:375-379. 1966.-A number of blue-green algae and photosynthetic bacteria synthesize arginine from glutamate via acetylated intermediates. Cell-free extracts of these photosynthetic microorganisms contain an N-acetyl glutamate phosphokinase, which is specifically inhibited by arginine. They also contain a transacetylase which forms ornithine from alphaN-acetyl ornithine and glutamate. The transacetylase appears to be specific for l-glutamate. Arginine synthesis and its regulation by feedback inhibition in photosynthetic microorganisms differ from that in Escherichia coli and other Enterobacteriaceae.     

Participation of ferredoxin in oxygen reduction in a photosynthetic electron-transport chain

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.     

Structural predictions on the 33 kDa extrinsic protein associated to the oxygen evolving complex of photosynthetic organisms

Modern computational methods for protein structure prediction have been used to study the structure of the 33 kDa extrinsic membrane protein, associated to the oxygen evolving complex of photosynthetic organisms. A multiple alignment of 14 sequences of this protein from cyanobacteria, algae and plants is presented. The alignment allows the identification of fully conserved residues and the recognition of one deletion and one insertion present in the plant sequences but not in cyanobacteria. A tree of similarity, deduced from pair-wise comparison and cluster analysis of the sequences, is also presented. The alignment and the consensus sequence derived are used for prediction the secondary structure of the protein. This prediction indicates that it is a mainly-beta protein (25–38% of -strands) with no more than 4% of -helix. Fold recognition by threading is applied to obtain a topological 2D model of the protein. In this model the secondary structure elements are located, including several highly conserved loops. Some of these conserved loops are suggested to be important for the binding of the 33 kDa protein to Photosystem II and for the stability of the manganese cluster. These structural predictions are in good agreement with experimental data reported by several authors.     

Quantitative relationship between two reaction centersin the photosynthetic system of blue-green algae

The quantitative relationship between reaction centers I andII was studied with blue-green algae Anabaena cylindrica, Anabaenavariabilis and Anacystis nidulans grown under different lightconditions. The number of reaction centers I was estimated fromthe P700 content and that of reaction centers II, from the O₂yield of repetitive short flashes. Supplementary determinationswere done with three other blue-green algae and one red alga.The maximum number of reaction centers II counted from the O₂yield of repetitive short flashes was markedly smaller thanthe total number of P700 in all algae tested when the algaewere grown under weak light; in the extreme case (Anabaena cylindrica),the ratio was only 0.258?0.015. This ratio became larger andclose to unity when the algae were grown under stronger light.Variation in the number of reaction centers in a single cellsuggested that reaction center I was a variable component. Ourresults indicate that the proportion of the two reaction centersmay markedly vary in blue-green algae depending on the growthconditions (Received November 13, 1978; )     

Consequences of iron deficiency on photosynthetic and respiratory electron transport in blue-green algae

Growth of Aphanocapsa in low iron media resulted in a decrease of the endogenous iron pool. Below a critical concentration photosynthetic electron transfer was specifically depressed. This was caused by a strong inhibition of the synthesis of cytochromes b-559 of PSII, cytochromes b-563, f-557, and the Rieske Fe-S center of the cytochrome complex and especially the Fe-S centers of PSI. The influence of iron limitation on respiration and chlorphyll formation was negligible.Paper presented at the FESPP meeting (Strasbourg, 1984)     

Changes in photosynthetic rate and pigment content of blue-green algae in Lake Mendota.

Blue-green algal blooms were present in Lake Mendota (Dane County, Wis.) from June to November 1976. Concentrations of total algal biomass and of particular algal species were monitored and compared with the pigment contents (chlorophyll a and phycocyanin) and photosynthetic rate of the algal populations. The specific photosynthetic rate (micrograms of C fixed per microgram of chlorophyll a per hour) was a good measure of the physiological state of the algae because this quantity increased just before each population increase and decreased before algal densities diminished. Since the quantity of light in the epilimnion which was available for photosynthesis by algal cells decreased in summer when the high algal densities attenuated incoming radiation, we investigated the possibility that the organisms would utilize lower light intensities more efficiently by increasing their pigment contents. Although some evidence of enhanced utilization of low light levels was found in the period from July to October, this result was not due to increasing chlorophyll and phycocyanin contents. There was a decrease in the phycocyanin content of the algae during this period, perhaps related to the availability of inorganic nitrogen.     

Changes in photosynthetic rate and pigment content of blue-green algae in Lake Mendota.

Blue-green algal blooms were present in Lake Mendota (Dane County, Wis.) from June to November 1976. Concentrations of total algal biomass and of particular algal species were monitored and compared with the pigment contents (chlorophyll a and phycocyanin) and photosynthetic rate of the algal populations. The specific photosynthetic rate (micrograms of C fixed per microgram of chlorophyll a per hour) was a good measure of the physiological state of the algae because this quantity increased just before each population increase and decreased before algal densities diminished. Since the quantity of light in the epilimnion which was available for photosynthesis by algal cells decreased in summer when the high algal densities attenuated incoming radiation, we investigated the possibility that the organisms would utilize lower light intensities more efficiently by increasing their pigment contents. Although some evidence of enhanced utilization of low light levels was found in the period from July to October, this result was not due to increasing chlorophyll and phycocyanin contents. There was a decrease in the phycocyanin content of the algae during this period, perhaps related to the availability of inorganic nitrogen.     

Participation of ferredoxin in oxygen reduction by the photosynthetic electron transport chain

Oxygen reduction by isolated pea thylakoids was studied in the presence of ferredoxin (Fd), Fd + NADP, and cytochrome c. At Fd concentrations optimal for NADP reduction, it contributed 30–50% of the reducing equivalents (as deduced by comparing the rates of oxygen reduction and light oxidation of reduced Fd). The oxygen reduction rate in the presence of Fd + NADP was 3–4 times lower than with Fd alone, and comparable to that with cyt c. It is supposed that the process involves a photosystem I component whose reaction with oxygen depends on the rate of electron efflux from the PS I terminal acceptors, and that this component is phylloquinone.     

Amino acid sequence of a ferredoxin from Bumilleriopsis filiformis, a yellow-green alga: relationship with red algae, protoflorideophyceae, and filamentous blue-green algae

The amino acid sequence of a [2Fe-2S] ferredoxin isolated from Bumilleriopsis filiformis, a yellow-green alga, was determined by using conventional techniques. It consisted of 98 amino acid residues with a microheterogeneity at the amino-terminus: Ala/Glu-Thr-Tyr-Ser-Val-Thr-Leu-Val-Asn-Glu-Glu-Lys-Asn-Ile-Asn-Ala-Val- Ile- Lys-Cys-Pro-Asp-Asp-Gln-Phe-Ile-Leu-Asp-Ala-Ala-Glu-Glu-Gln-Gly-Ile-Glu- Leu- Pro-Tyr-Ser-Cys-Arg-Ala-Gly-Ala-Cys-Ser-Thr-Cys-Ala-Gly-Lys-Val-Leu-Ser- Gly- Thr-Ile-Asp-Gln-Ser-Glu-Gln-Ser-Phe-Leu-Asp-Asp-Asp-Gln-Met-Gly-Ala-Gly- Phe- Leu-Leu-Thr-Cys-Val-Ala-Tyr-Pro-Thr-Ser-Asp-Cys-Lys-Val-Gln-Thr-His-Ala- Glu- Asp-Asp-Leu-Tyr. No prominent structural feature was noted in this ferredoxin in comparison with other homologous ferredoxins. From the structural comparison, B. filiformis was placed taxonomically close to filamentous blue-green algae and red algae.     

The effect of oxygen concentration on photosynthetic biomass production by algae

The effect of decreased oxygen concentration on photosynthetic biomass production was determined for Euglena gracilis Klebs strain z and Chlamydomonas reinhardtii Dangeard. At a constant carbon dioxide concentration of 0.03% (v/v), decreasing the oxygen concentration from 21% to 2% (v/v) gave a two-fold increase in dry-weight yield for E. gracilis; a result consistent with the operation of a functional glycollate pathway in this alga. A similar effect of oxygen concentration on dry-weight yield was not observed with C. reinhardtii.     

Calcium exchange and structural changes during the photosynthetic oxygen evolving cycle

PSII catalyzes the oxidation of water and reduction of plastoquinone in oxygenic photosynthesis. PSII contains an oxygen-evolving complex, which is located on the lumenal side of the PSII reaction center and which contains manganese, calcium, and chloride. Four sequential photooxidation reactions are required to generate oxygen. This process produces five Sn-states, where n refers to the number of oxidizing equivalents stored. Calcium is required for oxygen production. Strontium is the only divalent cation that replaces calcium and maintains activity. In our previous FT-IR work, we assessed the effect of strontium substitution on substrate-limited PSII preparations, which were inhibited at the S3 to S0 transition. In this work, we report reaction-induced FT-IR studies of hydrated PSII preparations, which undergo the full S-state cycle. The observed difference FT-IR spectra reflect long-lived photoinduced conformational changes in the oxygen-evolving complex; strontium exchange identifies vibrational bands sensitive to substitutions at the calcium site. During the S1' to S2' transition, the data are consistent with an electrostatic or structural perturbation of the calcium site. During the S3' to S0' and S0' to S1' transitions, the data are consistent with a perturbation of a hydrogen bonding network, which contains calcium, water, and peptide carbonyl groups. To explain our data, persistent shifts in divalent cation coordination must occur when strontium is substituted for calcium. A modified S-state model is proposed to explain these results and results in the literature.     

The occurrence of the hydrogenase in some blue-green algae

Several blue-green algae were surveyed for the occurrence of the hydrogenase which was assayed by the oxyhydrogen or Knallgas reaction in the intact organisms. In aerobically grown cultures, the reaction was detectable in Anabaena cylindrica, Nostoc muscorum and in two Anabaena variabilis species, whereas virtually no activity was observed in Anacystis nidulans and Cyanophora paradoxa. In these latter two algae, the reaction was, however, found after growth under molecular hydrogen for several days, which drastically increased the activity levels with all the algae tested. In the nitrogen fixing species, the activity of the Knallgas reaction was enhanced when all combined nitrogen was omitted from the media. H₂ and hydrogenase could not significantly support the CO₂-fixation in photoreduction experiments with all blue-green algae investigated here. Hydrogenase was assayed by the dithionite and methyl viologen dependent evolution of hydrogen and was found to be present with essentially the same specific activity levels in preparations of both heterocysts and vegetative cells from Anabaena cylindrica. Na₂S₂O₄ as well as H₂ supported the C₂H₂-reduction of the isolated heterocysts. The H₂-dependent C₂H₂-reduction did not require the presence of oxygen but was strictly light-dependent where H₂ served as an electron donor to photosystem I of these cells. It is concluded that hydrogen can be utilized by two different pathways in blue-green algae.Abbreviations Chl chlrophyll - CP creatine phosphate - CP kinase creatine phosphokinase - DCMU N-(3,4-dichlorophenyl)N,N-dimethylurea