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At least 739 records · Page 41Linked to original sources
PubMed1969

Light-induced changes in the fluorescence yield of chlorophyll A in vivo. IV. The effect of preillumination on the fluorescence transient of Chlorella pyrenoidosa.

The fluorescence transient of Chlorella pyrenoidosa, excited by saturating blue light, has a base level O, hump I, dip D, peak P, and at 1.5 sec a quasi-steady level S (12). With 2 sec exciting exposures and 4 min dark periods, preillumination-1 (lambda >/= 690 nm, intensities 1-750 ergs/sec-cm(2) incident), replacing the dark periods, lowers I more effectively than preillumination-2 (650 nm </= lambda </= 680 nm) in both aerobic and anaerobic cells. Results indicate that the intersystem electron transport pool A as well as the primary electron acceptor of pigment system II Q (fluorescence quencher) is normally being reduced at I. Preillumination-1 lowers and delays P. Preillumination-2 (absorbed by both pigment systems) also lowers P, but delays P only at low intensity; at high intensity it hastens P. Preillumination-1 raises S while preillumination-2 lowers S. With 30 instead of 2 sec exciting light exposures, preillumination-1 causes a large S increase, and at low intensity a P increase. The S effects seem to be of a long-term nature (26-29) rather than rapid changes in the redox state of Q. As exciting light intensity increases, fluorescence yield at P increases three-fold maximally. The ratio of P (anaerobic) to O (aerobic) is 5.5. These high ratios restrict the Franck-Rosenberg model of photosynthesis (13), which is based on fluorescence yield doubling.

Chlorophyll↗
PubMed2000

Heterotrophic production of biomass and lutein by Chlorella protothecoides on various nitrogen sources.

The effects of nitrate, ammonium, and urea as nitrogen sources on the heterotrophic growth of Chlorella protothecoides were investigated using flask cultures. No appreciable inhibitory effect on the algal growth was observed over a nitrogen concentration range of 0.85-1.7 g l(-)(1). In contrast, differences in specific growth rate and biomass production were found among the cultures with the various nitrogen compounds. The influence of different nitrogen sources at a concentration equivalent to 1.7 g l(-)(1) nitrogen on the heterotrophic production of biomass and lutein by C. protothecoides was investigated using the culture medium containing 40 g l(-)(1) glucose as the sole carbon and energy source in fermentors. The maximum biomass concentrations in the three cultures with nitrate, ammonium, and urea were 18.4, 18.9, and 19.6 g l(-)(1) dry cells, respectively. The maximum lutein yields in these cultures were between 68.42 and 83.81 mg l(-)(1). The highest yields of both biomass and lutein were achieved in the culture with urea. It was therefore concluded that urea was the best nitrogen source for the production of biomass and lutein. Based on the experimental results, a group of kinetic models describing cell growth, lutein production, and glucose and nitrogen consumption were proposed and a satisfactory fit was found between the experimental results and predicted values. Dynamic analysis of models demonstrated that enhancing initial nitrogen concentration in fermentor cultures, which correspondingly enhances cell growth and lutein formation, may shorten the fermentation cycle by 25-46%.

Journal Article↗
PubMed2000

Possible involvement of a 72-kDa polypeptide in nucleotide excision repair of Chlorella pyrenoidosa identified by affinity adsorption and repair synthesis assay.

A DNA repair synthesis assay monitoring nucleotide excision repair (NER) was established in cell-free extracts of unicellular alga Chlorella pyrenoidosa using cisplatin- or mitomycin C-damaged plasmid DNA as the repair substrate. The algal extracts promoted a damage-dependent increase in 32P-dATP incorporation after normalization against an internal control. To identify the proteins responsible for NER, a biotin-labeled duplex 27 mer (2 µg) irradiated with or without UV (27 kJ m(-2)) was immobilized on streptavidin-conjugated agarose beads and incubated with C. pyrenoidosa extracts (50 µg) to pull down repair proteins. The extracts post incubation with beads carrying unirradiated 27 mer promoted an eightfold increase in repair synthesis in plasmid DNA (1 µg) damaged by 16.8 pmol of cisplatin. The extracts obtained after affinity adsorption with UV-damaged DNA ligand, however, failed to repair plasmid DNA treated with cisplatin, reflecting that some proteins crucial to NER had been sequestered by the damaged 27 mer. A polypeptide approximately 70-72 kDa in molecular mass was found to bind much more strongly to the damaged DNA than to the control DNA after analyzing the proteins bound to the beads by SDS-PAGE, and this polypeptide is believed to play a role in NER in C. pyrenoidosa.

Journal Article↗
PubMed1998

Abolishing cadmium toxicity in Chlorella vulgaris by ascorbic acid, calcium, glucose and reduced glutathione.

Addition of ascorbic acid, calcium (Ca2+), glucose and reduced glutathione (GSH) to the cadmium (Cd2+)-amended Kuhl medium significantly accelerated the growth and chlorophyll content of Chlorella vulgaris. This enhancement was found to be dose dependent. Their relative effectiveness against Cd2+ on growth and chlorophyll content has been arranged as GSH > Ca2+ > glucose > ascorbic acid. However, Ca2+ offered more protection against Cd2+ toxicity on protein contents, followed by ascorbic acid, GSH and glucose. The different concentrations of all amelioratives completely alleviated the toxicity of Cd2+ on total carbohydrates to exceed the control level. Photosynthetic oxygen evolution showed more response to Ca2+ and glucose in alleviating Cd2+ toxicity. On the other hand, at certain concentrations, GSH, Ca2+, ascorbic acid and glucose stimulated respiratory oxygen uptake over the control level. The uptake of Cd2+ dropped significantly in cultures supplemented with 20 microM ascorbic acid, glucose and GSH, while Ca2+ (30 microM) significantly lowered the Cd2+ uptake by 58% indicating that Ca2+ had a more antagonistic effect against Cd2+.

Journal Article↗
PubMed2000

Effects of levulinic acid on 5-aminolevulinic acid production in heterotrophic cultures of Chlorella regularis YA-603.

To investigate the effects of levulinic acid (LA) on extracellular 5-aminolevulinic acid (ALA) accumulation, a heterotrophic culture of Chlorella regularis YA-603 in basal medium containing 0 to 60 mM of LA was carried out. It was found that the extracellular and total ALA concentrations increased, while the chlorophyll (CHL) concentration was the same above initial LA concentrations of 30 mM, with an increasing initial LA concentration up to 50 mM. In the presence of an initial LA concentration of 60 mM, however, the specific growth rate decreased markedly. This suggested that excessive LA exerted a negative effect on ALA production because it also directly affected cellular growth. The relationship between the initial LA and total ALA concentrations mentioned above indicates that LA could promote the ALA-producing activity. Kinetic analysis revealed that an LA concentration of between 30 to 50 mM in the culture broth gave the maximum specific production rate of ALA ((q(ALA))max). When LA was added repeatedly to maintain this optimum range of LA concentration, (q(ALA))max could be maintained at a relatively high level for a longer period, and the maximum concentration of ALA reached 3.86 mM.

Journal Article↗
PubMed2000

Two catalytic domains of Chlorella virus CVK2 chitinase.

VChti-1 chitinase encoded by the Chlorella virus CVK2 contained two catalytic domains belonging to family 18 glycosyl hydrolases. The first catalytic domain on a C-terminal-truncated derivative of vChti-1 generated exclusively chitobiose from chitotetraose, chitohexaose, and colloidal high-molecular mass chitin in the enzyme reaction, a typical characteristic of an exochitinase. In contrast, N-acetylglucosamine was produced from chitobiose as well as from chitooligosaccharides by the second catalytic domain on an N-terminal-truncated derivative of vChti-1. Therefore, the second domain possessed N-acetylglucosaminidase activity as well as endochitinase activity. The presence of two catalytic domains with different enzymatic properties in the viral enzyme seems to be necessary for hydrolyzing natural substrates in a cooperative fashion.

Journal Article↗
PubMed2000

Effect of osmotic stabilizers on protoplast generation of Chlorella ellipsoidea yellow/white color mutants.

The effect of osmotic stabilizers on protoplast formation of yellow/white color mutants of Chlorella ellipsoidea was studied. The UF-1 strain, one of the mutants, had the same growth rate as the parent C. ellipsoidea at 4.02 microE/m2/s and no reversion to normal cells at 0-26.8 microE/m2/s. Therefore, protoplast formation from UF-1 was carried out, and it was found that the yield of protoplasts was 93% in the medium containing 1.0 M NaCl as an osmotic stabilizer.

Journal Article↗
PubMed1999

Effect of glycine on 5-aminolevulinic acid biosynthesis in heterotrophic culture of Chlorella regularis YA-603.

Chlorella regularis strain YA-603 was previously found to exhibit a comparatively high growth rate and improved 5-aminolevulinic acid (ALA) productivity when cultured heterotrophically. Although the universal tetrapyrrole precursor ALA is synthesized from glutamate in algae and higher plants, in this study the addition of glutamate to the medium did not enhance ALA production in the heterotrophic culture of C. regularis YA-603. On the other hand, the addition of glycine, which is a precursor of ALA biosynthesis via the Shemin pathway in animal cells and some bacteria, enhanced both the specific growth rate and ALA production. Moreover, when a second glycine addition was made during the culture, the ALA concentration increased by about 1.5 times compared to that obtained with one glycine addition. From these results, it is suggested that the Shemin pathway contributes to ALA production, and that addition of glycine in the heterotrophic culture of C. regularis YA-603 can significantly increase the amount of ALA produced.

Journal Article↗
PubMed2002

Non-photochemical quenching of chlorophyll fluorescence in Chlorella fusca acclimated to constant and dynamic light conditions.

Non-photochemical quenching of chlorophyll fluorescence (NPQ) involves dissipation of light energy in the photosynthetic apparatus via a number of physiologically distinct processes. The relationships among NPQ, the (de)epoxidation state of the xanthophyll cycle pigments and state transitions was studied in the green alga Chlorella fusca, acquired from six differently light-acclimated continuous cultures. A 10 h light and 14 h darkness, periodicity was obeyed in all cultures. Three cultures received a high total daily irradiance, three others a low one. High and low irradiances were each dosed in three different modes at constant supply, with sine shape intensity modulation, or as a sine with superimposed oscillations. In the constant supply mode, but not for the sine and oscillating modes, high-light rendered a three-fold higher xantophyll cycle pigment content than low-light. Dynamic interconversion of xantophyll cycle pigments was restricted to high-light cultures. NPQ followed the kinetics of the light supply mode and was highest in high light cultures. In low-light cultures, NPQ correlated mainly to state transitions. These observations were supported by experiments with dithiothreithol-treated samples. The relative impact of xantophyll cycle operation and state transitions on NPQ in green algae from different light climates will be discussed with reference to higher plants.

Journal Article↗
PubMed2001

The inhibition of the carbon concentrating mechanism of the green alga Chlorella saccharophila by acetazolamide.

The effects of the carbonic anhydrase (CA) inhibitors acetazolamide (AZ) and dextran-bound sulfonamide (DBS) on HCO3--dependent O2 evolution in Chlorella saccharophila were evaluated. Addition of 4 µM AZ or 0.4 mg ml-1 DBS to photosynthesizing cells reduced the O2 evolution rate at low dissolved inorganic carbon (DIC) concentration, decreased the size of the intracellular acid-labile carbon pool, and decreased the apparent affinity of the cells for DIC. Measurement of the whole-cell affinity of cells for CO2 and HCO3- in the presence and absence of inhibitors indicated that active HCO3- transport was inhibited by AZ and DBS. The inhibition of HCO3- transport was independent of the inhibition of external and internal CA. These results suggest that the active uptake of HCO3- occurs initially by the interaction of HCO3- and a CA-like transporter.

Journal Article↗
PubMed1967

Interrelationships between fatty acid biosynthesis and acyl-lipid synthesis in Chlorella vulgaris.

1. Fatty acid synthesis from [2-(14)C]acetate by Chlorella vulgaris cells grown and incubated in the dark is limited almost entirely to the production of saturated and monoenoic acids. 2. In light-incubated cells, both saturated and polyunsaturated fatty acids are rapidly synthesized. 3. Two groups of lipids can be distinguished in both dark- and light-incubated cells. The first group, consisting of phosphatidyl-glycerol, monogalactosyl diglyceride, lecithin and neutral glyceride, has a very high turnover rate for certain fatty acids. The second group, consisting of digalactosyl diglyceride, sulpholipid, phosphatidylethanolamine and phosphatidylinositol, has a slow turnover of fatty acids. 4. The lipids with rapid fatty acid turnover may be involved in the sequences of saturated and unsaturated fatty acid synthesis. A classification of lipids is made on the basis of their suggested functions.

Acetates↗
PubMed1967

The purification and properties of isocitrate lyase from Chlorella.

1. Isocitrate lyase (threo-d(s)-isocitrate glyoxylate-lyase, EC 4.1.3.1) has been purified from acetate-adapted cells of Chlorella pyrenoidosa. 2. The final preparation was homogeneous by the criteria of sedimentation, diffusion and polyacrylamide-gel electrophoresis. 3. The sedimentation coefficient (S(20,w)) was 9.04x10(-13)sec. and the diffusion coefficient (D(20,w)) 4.62x10(-7)cm.(2)/sec.; from these values the molecular weight of the enzyme was calculated to be 170000 and its Stokes radius to be 4.63x10(-7)cm. 4. The elution of the enzyme from Sephadex G-100 was studied and estimates of molecular weight and Stokes radius were obtained from the elution data. 5. The turnover number of the enzyme was 5950moles of glyoxylate formed/min./mole of enzyme at 30 degrees . 6. With threo-d(s)(+)-isocitrate as substrate, the K(m) of the enzyme was 0.023mm.

Buffers↗
PubMed1968

The stereochemistry of desaturations of long-chain fatty acids in Chlorella vulgaris.

1. A study was made of the stereospecificity of hydrogen removal in the sequential desaturations performed by intact cells of Chlorella vulgaris in the biosynthesis of oleic acid, linoleic acid and alpha-linolenic acid. 2. By use of erythro- and threo-9,10-(2)H(2)-, -12,13-(2)H(2)- and -15,16-(2)H(2)-labelled precursors, it was demonstrated that the pair of hydrogen atoms removed from each of these positions had the cis relative configuration. 3. That the hydrogen atoms removed in oleic acid and linoleic acid formation were of the d absolute configuration was proved by use of d- and l-9-(3)H-and -12-(3)H-labelled precursors. 4. The presence of a substantial kinetic isotope effect of deuterium at both positions of the putative double bond was indicated, suggesting that the mechanism of desaturation involves simultaneous concerted removal of the pair of hydrogen atoms.

Deuterium↗
PubMed1970

The pathway of glycollate utilization in Chlorella pyrenoidosa.

1. Exogenous glycollate was rapidly metabolized in both the light and the dark by photoautotrophically grown Chlorella pyrenoidosa. 2. The incorporation of (14)C from [1-(14)C]glycollate by these cells was inhibited by the tricarboxylic acid-cycle inhibitors monofluoroacetate, diethylmalonate and arsenite, and also by alpha-hydroxypyrid-2-ylmethanesulphonate and isonicotinylhydrazine. 3. Short-term kinetic experiments showed over 80% of the total (14)C present in the soluble fraction from the cells to be in glycine and serine after 10s. This percentage decreased with time whereas the percentage radioactivity in glycerate increased for up to 30s then remained steady. The percentage of the total radioactivity present in citrate increased over the experimental period. Malate was the only other tricarboxylic acid-cycle intermediate to become labelled. 4. The kinetic and inhibitor experiments supported the following pathway of glycollate incorporation: glycollate --> glyoxylate --> glycine --> serine --> hydroxypyruvate --> glycerate --> 3-phosphoglycerate --> 2-phosphoglycerate --> phosphoenolpyruvate --> pyruvate --> acetyl-CoA. 5. The specific activities of the enzymes catalysing this metabolic sequence in cell-free extracts were great enough to account for the observed rate of glycollate metabolism of 0.25mumol/h per mg dry wt. of cells in the light.

Carbon Isotopes↗
PubMed1970

Disappearance of isocitrate lyase enzyme from cells of Chlorella pyrenoidosa.

1. When acetate-adapted cells of Chlorella are suspended in nitrogen-free medium and supplied with glucose, isocitrate lyase activity disappears from the cells at a rate of about 9%/h. This loss of activity is shown to be accompanied by loss of isocitrate lyase protein. 2. When isocitrate lyase activity is assayed in intact cells after freezing and thawing, the rate of loss of activity after addition of glucose approaches 20%/h. 3. It is shown, by using (35)S, that the rate of turnover of isocitrate lyase protein is somewhat lower than that of other major soluble proteins; general protein turnover during nitrogen starvation, and after glucose addition, is too slow to account for the rate of loss of isocitrate lyase protein. 4. Disappearance of isocitrate lyase activity must result from a mechanism that allows degradation of this specific protein under conditions of limiting nitrogen supply.

Acetates↗
PubMed2006

Chlorella virus MT325 encodes water and potassium channels that interact synergistically.

Fast and selective transport of water through cell membranes is facilitated by water channels. Water channels belonging to the major intrinsic proteins (MIPs) family have been found in all three domains of life, Archaea, Bacteria, and Eukarya. Here we show that Chlorella virus MT325 has a water channel gene, aqpv1, that forms a functional aquaglyceroporin in oocytes. aqpv1 is transcribed during infection together with MT325 kcv, a gene encoding a previously undescribed type of viral potassium channel. Coexpression of AQPV1 and MT325-Kcv in Xenopus oocytes synergistically increases water transport, suggesting a possible concerted action of the two channels in the infection cycle. The two channels operate by a thermodynamically coupled mechanism that simultaneously alters water conductance and driving force for water movement. Considering the universal role of osmosis, this mechanism is relevant to any cell coexpressing water and potassium channels and could have pathological as well as basic physiological relevance.

Amino Acid Sequence↗
PubMed1981

Glucose induces two amino acid transport systems in Chlorella.

In autotrophically grown Chlorella cells, glucose induces a hexose transport system but, at the same time, the synthesis of two amino acid transport systems is also induced. Thus, the rates of uptake of glycine, L-alanine, L-proline, and L-serine, all of which compete with each other for entry into the cells, increase more than 100-fold when the algae are pretreated with glucose. The rates of L-arginine and L-lysine uptake increase by a factor of 25 to 50. The accumulation of proline and arginine within the cells amounts to 200- and 600-fold, respectively. Glucose does not cause the positive effect on amino acid uptake by serving as metabolic substrate because the nonmetabolizable 6-deoxyglucose also acts as inducer. Cycloheximide prevents the induction. The induced transport system for the four neutral amino acids has a turnover with a half-life of 7 hr, which corresponds closely to the half-life of the hexose transport system. The transport system for the basic amino acids, on the other hand, disappears with a half-life of 25 hr.

Alanine↗
PubMed2001

Role of nucleotidyl transferase motif V in strand joining by chlorella virus DNA ligase.

ATP-dependent DNA ligases, NAD(+)-dependent DNA ligases, and GTP-dependent RNA capping enzymes are members of a covalent nucleotidyl transferase superfamily defined by a common fold and a set of conserved peptide motifs. Here we examined the role of nucleotidyl transferase motif V ((184)LLKMKQFKDAEAT(196)) in the nick joining reaction of Chlorella virus DNA ligase, an exemplary ATP-dependent enzyme. We found that alanine substitutions at Lys(186), Lys(188), Asp(192), and Glu(194) reduced ligase specific activity by at least an order of magnitude, whereas substitutions at Lys(191) and Thr(196) were benign. The K186A, D192A, and E194A changes had no effect on the rate of single-turnover nick joining by preformed ligase-adenylate but affected subsequent rounds of nick joining at the ligase adenylation step. Conservative substitutions K186R, D192E, and E194D partially restored activity, whereas K186Q, D192N, and E194Q substitutions did not. Alanine mutation of Lys(188) elicited distinctive catalytic defects, whereby single-turnover nick joining by K188A-adenylate was slowed by an order of magnitude, and high levels of the DNA-adenylate intermediate accumulated. The rate of phosphodiester bond formation at a pre-adenylated nick (step 3 of the ligation pathway) was slowed by the K188A change. Replacement of Lys(188) by arginine reversed the step 3 arrest, whereas glutamine substitution was ineffective. Gel-shift analysis showed that the Lys(188) mutants bound stably to DNA-adenylate. We infer that Lys(188) is involved in the chemical step of phosphodiester bond formation.

Adenosine Triphosphate↗