[Relationship between substrats, respiration and structure of mitochondria in Euglena gracilis (Z)]

A possible role of the Na(+)/K(+)-ATPase for O(2) production from H(2)O(2)

We are attempting to supply a new insight on interaction between Na(+)/K(+)-ATPase and H(2)O(2). We demonstrate that in vitro the Na(+)/K(+)-ATPase, a non heme-protein, is able to disproportionate H(2)O(2) catalatically into dioxygen and water, as well as C(40) catalase. By polarography, we quantify O(2) production and by Raman spectroscopy H(2)O(2) consumption. A comparative analysis of kinetics parameters relative to O(2) production shows that for Na(+)/K(+)-ATPase the affinity of the catalytic site able to transform H(2)O(2) into O(2) is twice weaker than that for C(40) catalase. It also shows that the molar activity for O(2) production is 300-fold weaker for ATPase than for catalase. Inhibitors, pH and GSH studies highlight the differences between the heme- and nonheme-proteins. Indeed, for C(40), NaN(3) is strongly inhibiting, but much less for ATPase. The pH range for the catalatic activity of ATPase is wide (6.5 to 8.5), while it is not for C(40) catalase (optimum at pH 8). The Na(+)/K(+)-ATPase catalatic activity is reduced in presence of glutathione, while it is not the case with C(40) catalase.

Copper-adenine catalyst for O(2) production from H(2)O(2)

In solutions of CuCl2 and adenine copper can be bound to adenine. Two Cu(adenine)(2) complexes [Cu(C(5)H(5)N(5))(2)]2+/Cu(C(5)H(4)N(5))(2)] are in equilibrium with free adenine. Copper-adenine complexes present a catalytic activity (e.g., H(2)O(2) disproportionation into O(2) and water) but depending on complex concentration H(2)O(2) also strongly oxidizes the adenine within the complexes. Raman spectroscopy quantifies copper-adenine complex formation and H(2)O(2) consumption; polarography quantifies O(2) production. As for C(40) catalase, optimal catalytic capacities depend on physiological conditions, such as pH and temperature. The comparative analysis of kinetic parameters shows that the affinity for H(2)O(2) of Cu(adenine)(2) is 37-fold lower than that of C(40) catalase and that the molar activity for O(2) production is 200-fold weaker for Cu(adenine)(2) than for the enzyme. In the 10(-6)-10(-3) M range, the strong decrease of activity with raising complex concentration is explained by aggregation or stacking, which protects Cu(adenine)(2) entities from H(2)O(2) oxidation, but also decreases O(2) production.

Oxygen-evolving system and secondary quinonic acceptors are highly reduced in dark adapted Euglena cells: A thermoluminescence study

Characteristics of thermoluminescence glow curves were compared in three types of Euglena cells: (i) strictly autotrophic, Cramer and Myers cells; (ii) photoheterotrophic cells sampled from an exponentially growing culture containing lactate as substrate repressing the photosynthetic activity; (iii) semiautotrophic cells, sampled when the lactate being totally exhausted, the photosynthesis was enhanced.In autotrophic and semiautotrophic cells, composite curves were observed after series of two or more actinic flashes fired at -10°C, which can be deconvoluted into a large band peaking in the range 12-22°C and a smaller one near 40°C, This second band presents the characteristics of a typical B band (due to S2/3QB (-) recombination), whereas the first one resembled the band, shifted by -15-20°C, which is observed in herbicide resistant plants. The amplitude of this major band, which was in all cases very low after one flash, exhibited oscillations of period four but rapidly damping, with maxima after two and six flashes. In contrast, photoheterotrophic Euglena displayed single, non-oscillating curves with maxima in the range 5-10°C.In autotrophic and semiautotrophic cells, oxidizing pretreatments by either a preillumination with one or more (up to twenty-five) flashes, or a far-red preillumination in the presence of methylviologen, followed by a short dark period, induced thermoluminescence bands almost single and shifted by +3-5°C, or +12°C, respectively. In autotrophic cells, far-red light plus methyl viologen treatment induced a band peaking at 31°C, as in isolated thylakoids from Euglena or higher plants, while it had barely any effect in photoheterotrophic cells.Due to metabolic activities in dark-adapted cells, a reduction of redox groups at the donor and acceptor sides of PS II dark-adapted cells is supposed to occur. Two different explanations can be proposed to explain such a shift in the position of the main band in dark-adapted autotrophic control. The first explanation would be that in these reducing conditions a decreasing value of the equilibrium constant for the reaction: SnQA (-)QB⇌SnQAQB (-), would determine the shift of the main TL band towards low temperatures, as observed in herbicide resistant material. The second explanation would be that the main band would correspond to 'peak III' already observed in vivo and assigned to S2/3QB (2-) recombinations.

Translational regulation of protein synthesis during light-induced chloroplast development in Euglena

Control of gene expression in Euglena was examined during light-induced chloroplast development. Greening was achieved under standard conditions which allowed the synthesis of all plastid proteins in both cytoplasmic and chloroplastic compartments, or under experimentally modified conditions inducing the preferential synthesis of the photosystem II (PSII) light-harvesting antenna or reaction centers. The relative composition of total mRNAs in cellular, cytoplasmic or chloroplastic fractions, as analyzed by their in-vitro translation products in cell-free systems did not significantly change during the in-vivo protein-synthesis processes which are specific to each greening system. By contrast, cytoplasmic polysomal mRNAs extracted during the selective recovery phase of PSII light-harvesting antennae provided a major in-vitro synthesis product of 28 kDa which could correspond to a precursor of the main 26-kDa apoprotein of the light-harvesting chlorophyll a/b protein complex. Similarly, the in-vivo selective synthesis of the 41-kDa and 51-kDa polypeptides of PSII reaction centers was concomitant with an enrichment of plastid polysomes in mRNA species coding for polypeptides of the same molecular weight. These observations confirm that protein synthesis during chloroplast development in Euglena is weakly regulated at the transcription level and they demonstrate that translational regulation occurs in both the cytoplasmic and the chloroplastic compartments.

Paramylon synthesis by Euglena gracilis photoheterotrophically grown under low O2 pressure : Description of a mitochloroplast complex

Special culture conditions for Euglena gracilis Z and ZR are described. They induce interactions between the chloroplast and mitochondrial metabolisms leading to paramylon synthesis. When grown in continuous light under pure nitrogen and in the presence of lactate as the sole carbon source, sugar synthesis occurs during the first 24 h of culture with the participation of both mitochondria (using lactate) and of chloroplasts (fixing CO2 from lactate decarboxylation). The activities of ribulose bisphosphate carboxylase, phosphoenolpyruvate carboxylase, and phosphoenolpyruvate carboxykinase are very high and mitochondria and chloroplasts develop then a common network of vesicles in which paramylon grains can be seen. Electron micrographs demonstrate membrane continuity between the two types of organelles. Occasionally the mitochondrial matrix and the chloroplast stroma are separated by only a unit membrane.

Evolution of carboxylating enzymes involved in paramylon synthesis (phosphoenolpyruvate carboxylase and carboxykinase) in heterotrophically grown Euglena gracilis

Heterotrophically grown Euglena synthesize grains of paramylon, its reserve carbohydrate, in a vesicular complex of mitochondrial origin. A CO2 fixation activity in dark grown Euglena was demonstrated in the mitochondria via paramylon. At the beginning of the exponential phase of growth, the activity of phosphoenolpyruvate carboxykinase increases before the augmentation of paramylon.At the end of the exponential phase, the activity of this enzyme decreases, and low residual levels persist in the transition and stationary phases of growth. The activity of phosphoenolpyruvate carboxylase evolves inversely during the heterotrophic growth of the algae in succinate- or a lactate-containing medium. A compartmentalized scheme of carbon metabolism in mitochondria is presented.

[Study of the regulation of plastid development in Euglena gracilis. II. Functional localisation and synthesis of ribosomal chloroplast particles (author's transl)]

Chloroplast ribosomes in greening cells of Euglena gracilis are found either in the stroma or bound to thylakoid membranes. The membrane-bound chloroplast ribosomes are of two main types: those which can be released by 0.5 M KCl or by puromycin and 0.5 M KCl, and those which are released by detergent (deoxycholate or Triton X-100) and KCl. The ribosomes which are released by puromycin are presumably bound to chloroplast membrane by nascent peptide chains. Ribosomes released by puromycin are found only during the course of plastidial differentiation at the time of active thylacoid membrane synthesis. Following greening, those ribosomes remain bound to the membranes but can be removed by KCl alone. An analysis of RNA labelling showed that 30-S but not 53-S subunits of membrane-bound ribosomes are of uniform specific activity. This suggests that 30-S subunit exchange in a common pool while 53 S subunits remain membrane bound and do not exchange in a common pool. Membrane-bound chloroplast ribosomes which are released either by puromycin or by detergent are originally derived from loosely bound particles, released by 0.5 M KCl.

[Synthesis of heavy RNA during a cell cycle in Euglena gracilis]

In a previous investigation we had observed discontinuous RNA synthesis during the cell cycle of Euglena gracilis grown synchronously in the light or in the dark. In the present study, we analyse which RNA species are synthesized during the several phases of the cell cycle. During cell division, sedimentation analysis of RNA on sucrose gradients and polyacrylamide-agarose gel electrophoresis show a labeled 30 S RNA peak having a molecular weight of 2.1x10(6) daltons. This type of RNA seems heterogeneous on the basis of its behaviour in polyacrylamide-agarose gel electrophoresis, and is composed of at least two different molecular species. Their synthesis is inhibited by cycloheximide (50 μg/ml). This RNA is degraded preferentially to 13 S material. By autoradiography using a light microscope, we can observe extensive labeling in the nucleolus of dividing cells. Kinetics of labeling, chase experiments, and concomitant synthesis of heavier RNA (40 S and 35 S) tend to identify the 30 S RNA as the immediate precursor of one or both cytoplasmic ribosomal RNA molecules.

[Comparison of specific synthesis of RNA in synchronized Euglena gracilis (Z) grown on lactate medium in the dark and in the light, and a study of the mitochondria]

Synchronization of Euglena gracilis (Z) on lactate medium is shown to be independent of illumination. The existence of a mitochondrial cycle in lightgrown as well as in dark-grown Euglena is demonstrated. When RNA synthesis is studied by pulse labeling with tritiated uracil in synchronously growing cells, a discontinuous RNA synthesis is found. Two peaks of preferential RNA synthesis in dark-grown cells and three peaks in light-grown cells are seen; the significance of the third peak of RNA synthesis in light-grown Euglena is discussed.