Uptake of cobalamin by Euglena mitochondria

Cobalamin uptake by Euglena mitochondria is a biphasic process, consisting of energy-independent cobalamin-binding to mitochondrial membranes and energy-dependent active transport. The energy-dependent phase of cobalamin uptake is not dependent on mitochondrial respiration, but on the presence of ATP within the mitochondrial matrix. The dissociation constant of the energy-independent cobalamin-binding reaction is estimated to be 0.45 nM. Inhibition of the mitochondrial cobalamin uptake by a variety of cobalamin analogues indicates that Euglena mitochondria have an absolute requirement for the complete cobalamin molecule with an alpha-axial ligand (the cobalt-coordinated nucleotide) and an intact b-propionamide side-chain. Thus, the Euglena mitochondrial cobalamin uptake system is highly specific for the cobalamin structure. The cobalamin taken up by the Euglena mitochondria cannot be exchanged with exogenous cobalamin. All of the mitochondrial cobalamin is associated with three proteins with molecular masses of > 700,000 (16.3%), 160,000 (7.4%), and 35,000 (76.3%). They occur in the soluble fraction of mitochondria, suggesting that these cobalamin-binding proteins or cobalamin-dependent enzymes play an important role in cobalamin accumulation and metabolism within the mitochondria.

Influence of ofloxacin on chloroplasts and mitochondria in Euglena gracilis

Ofloxacin (CAS 83380-47-6), a representative of new quinolones, which exerts inhibitory activity against DNA gyrase in bacteria, damages both semiautonomous organelles in Euglena gracilis: chloroplasts and partly mitochondria. The action of ofloxacin on these organelles was analysed by transmission electron microscopy. The first symptoms of ofloxacin treatment were mass aberrations of chloroplasts with subsequent diluting out of these pathological organelles from the cells, so giving rise to the heterotrophic mutants. The loss of chloroplasts is hereditary. Changes in ultrastructure of mitochondria were observed too. Cup-like (in sections ring-like) mitochondria represented the most frequent abnormalities of these organelles induced by the drug. After repeated subcultivations on ofloxacin-free media the number of damaged mitochondria gradually decreased to the normal.

Microsomal ethanol-oxidizing system in Euglena gracilis. Similarities between Euglena and mammalian cell systems

1. ADH activity of Euglena grown with 50 mM ethanol decreased, but MEOS activity increased with a corresponding increase in the total amount of cytochrome P-450. 2. Phenobarbital treatment increased the total amount of cytochrome P-450. 3. CO and KCN, cytochrome P-450 ligands, diminished acetaldehyde formed from ethanol oxidation by MEOS. 4. The amounts of NAD(P)H cytochrome c reductases and cytochrome b5 type, components of microsomal monooxygenase reaction, have been spectrophotometrically measured. 5. NAD(P)H cytochrome c reductases activities were induced by phenobarbital. 6. DMSO, an inhibitor of rabbit MEOS, inhibited O2 consumption (11-20%) by Euglena grown with an ethanol, but not a lactate medium. 7. These studies indicate the presence of cytochrome P-450-dependent MEOS in Euglena similar to that in the mammalian hepatic cell.

Use of a microbial model for the determination of drug effects on cell metabolism and energetics: study of citrulline-malate

Euglena gracilis can be used as a microbial model to study the effect of drugs on lactate metabolism and gluconeogenetic synthesis. The cell growth and metabolism have been characterized in a 33 mM lactate medium, non-supplemented or supplemented by dl-malate or by l-citrulline alone or by the compound formed by the stoichiometric combination of the two components: the citrulline-malate (Stimol). The malate of the complex accelerated the ammonium disappearance, while the citrulline facilitated the lactate consumption. A synergistic action of the complex, by comparison with the additive effects of the individual components, on most of the parameters studied was detected. A remarkable resistance to anoxia, and a quicker recovery under aeration of the cells supplemented with CM, were evident: after carbonation for 2 min the total nucleotides in the medium were increased by 44 per cent with an unchanged energy charge; and after a prolonged (20 min) anoxia followed by an aeration, the capacities of the cells to synthesize ATP in the presence of excesses of both ADP and phosphate were two-fold higher in Stimol treated cells than in control.

Isolation of a novel type-I fatty-acid synthetase from Euglena gracilis. Specific derepression in streptomycin-bleached cells

A novel, high-molecular-mass fatty-acid synthetase (FAS) complex has been isolated from streptomycin-bleached Euglena gracilis cells. The enzyme was purified 250-fold from the crude cell homogenate and subsequently migrated upon SDS/PAGE as a single band of molecular mass 270 kDa. This apparent subunit size of the purified protein contrasted with a smaller size of only 200 kDa which was exhibited by the same protein upon immunoblotting of the crude cell extract. The purified Euglena FAS complex cosediments in a sucrose density gradient with yeast FAS and, from this, both enzymes were concluded to have the same overall molecular mass of 2.3 MDa. The enzyme described in this paper appears to be a typical type-I FAS multienzyme which clearly differs from the E. gracilis FAS so far described. Instead, it appears to be organized structurally similar to the type-I FAS multienzymes of lower fungi. In vitro, the purified Euglena FAS complex synthesizes mainly palmitic acid, or its CoA ester, from acetyl CoA and malonyl CoA as substrates. The Km values for acetyl CoA and malonyl CoA are 20 microM and 31 microM, respectively. Similar to the FAS enzymes of other lower eucaryotes, the Euglena type-I FAS is a flavoprotein. In contrast to yeast FAS, however, the flavin cofactor appears to be covalently attached to the enzyme protein. By immunological techniques, the enzyme was shown to be absent in green as well as in etiolated E. gracilis cells, while being rapidly induced upon streptomycin bleaching of heterotrophically growing green cells. The data suggest an inverse correlation between organellar development and derepression of this FAS complex.

N-(phosphonomethyl)glycine (glyphosate) tolerance in Euglena gracilis acquired by either overproduced or resistant 5-enolpyruvylshikimate-3-phosphate synthase

Photoautotrophic cells of Euglena gracilis can be adapted to N-(phosphonomethyl)glycine (glyphosate) by cultivation in media with progressively higher concentrations of the herbicide. Two different mechanisms of tolerance to the herbicide were observed. One is characterized by the overproduction and 40-fold accumulation of the target enzyme. 5-enolpyruvylshikimate-3-phosphate synthase, in cells adapted to 6 mM N-(phosphonomethyl)glycine. The other is connected with a herbicide-insensitive enzyme. No evidence was obtained for the involvement of the putative multifunctional arom protein previously reported to be involved in the biosynthesis of aromatic amino acids in Euglena. Cells adapted to N-(phosphonomethyl)glycine excreted shikimate and shikimate 3-phosphate into the medium: the amounts depended on the actual concentration of the herbicide. Two-dimensional gel electrophoresis and determination of 5-enolpyruvylshikimate-3-phosphate synthase activity in crude extracts, as well as after separation by non-denaturing gel electrophoresis, revealed that the overproduction of the enzyme in adapted cells correlates with the accumulation of a 59-kDa protein. Overproduction of this 59-kDa protein resulted from a selectively increased level of a mRNA coding for a 64.5-kDa polypeptide which appeared in adapted cells, as shown by cell-free translation in the wheat germ system. In contrast to this quantitative, adaptive type of tolerance, the second mechanism causing tolerance to N-(phosphonomethyl)glycine in the Euglena cell line NR 6/50 was probably related to a qualitatively altered 5-enolpyruvylshikimate-3-phosphate synthase, which could not be inhibited by even 2 mM N-(phosphonomethyl)glycine in vitro. In agreement with this observation, the putatively mutated cell line excreted neither shikimate nor shikimate 3-phosphate into the growth medium containing N-(phosphonomethyl)glycine, even if cultivated in the presence of 20 mM or 50 mM N-(phosphonomethyl)glycine.

Activity of bleomycin in iron- and copper-deficient cells

Three models were used to examine the requirement of bleomycin (Blm) for iron (Fe) to carry out its antitumor or cytotoxic activity. Mice were made iron deficient by dietary means. Animals with depressed iron stores in liver and low plasma and ascites fluid iron supported Ehrlich tumor growth as well as mice maintained on a control diet. Bleomycin was equally effective against this tumor in iron-deficient mice as it was against the tumor in iron-sufficient controls. Likewise, nutrient copper deficiency did not change the efficacy of the drug. Ehrlich cells in culture were treated with a non-growth inhibiting concentration of the chelating agent, 1,10-phenanthroline before or during their exposure to bleomycin. Again, the treated cells were as sensitive to drug as controls, despite the fact that this ligand reduces cellular iron and zinc and can extract iron from Fe(II)Blm. Lastly, it was demonstrated that iron-depleted Euglena gracilis cells growing at reduced rates were as sensitive to growth inhibition by bleomycin as control cells.

Quinolones and coumarins eliminate chloroplasts from Euglena gracilis

Quinolones and coumarins were potent eliminators of chloroplasts from Euglena gracilis. There was a remarkable similarity between antichloroplastic and antibacterial activities of DNA gyrase inhibitors. Quinolones produced 100% chloroplast-free cells in concentrations which do not affect cell viability. Optimal conditions were exponential growth, continuous illumination, and neutral or slightly alkaline pH. Coumarins were more toxic than quinolones. Among the quinolones, ofloxacin was the most potent in eliminating chloroplasts. Among the coumarins, coumermycin A1 was the most potent. New quinolones and coumermycin A1 were able to induce the complete inability of originally green cells to form green colonies after 24 h of drug exposure, while clorobiocin and novobiocin required several days of exposure. Darkness, heat shock (42 degrees C, 10 min), or simultaneous treatment with chloramphenicol or rifampin decreased the potency of DNA gyrase inhibitors for producing chloroplast-free cells. Remarkably, in cells in which division was blocked by three different methods (resting medium, hyperthermic conditions [37 degrees C], or addition of cycloheximide), new quinolones and coumermycin A1 nevertheless eliminated chloroplasts. The antichloroplastic activity of DNA gyrase inhibitors is additional data suggesting an evolutionary relationship between chloroplasts and eubacteria.

Effect of elevated temperature on genotoxicity of chemotherapeuticals toward Euglena gracilis

A collection of 20 compounds was tested for their ability to induce a permanent loss of chloroplasts from Euglena gracilis cells under conditions increasing the sensitivity of the flagellate to genotoxic compounds, viz. in the resting medium and at an elevated temperature. Streptomycin, dihydrostreptomycin, gentamicin, kanamycin and partially chloramphenicol exhibited mutagenic effects. Eight antibiotics eliminated chloroplasts only from growing cultures and seven antibiotics did not induce the mutation at all.

A sulphate metabolizing centre in Euglena mitochondria

We have previously shown that a sulphate activating system is present on the outside of the inner mitochondrial membrane of Euglena gracilis Klebs. var. bacillaris Cori, but efforts to couple this system to ATP produced from oxidative phosphorylation were unsuccessful. In the present work we show that the concentration of Pi ordinarily used to support oxidative phosphorylation in these mitochondria (10 mM) inhibits sulphate activation completely; by reducing the concentration of Pi 10-fold, both processes proceeded normally. Sulphate activation under these conditions is inhibited nearly completely by the uncouplers of oxidative phosphorylation dinitrophenol (0.1 mM) and carbonyl cyanide m-chlorophenylhydrazone (CCCP) (0.2 microM). Sulphate reduction to form free cysteine, most of which appears outside the organelle, and in the cysteine of mitochondrial protein can be demonstrated in the same preparations, is membrane-bound and is inhibited by chloramphenicol (100 micrograms/ml), NaN3 (5 mM), KCN (100 microM); dinitrophenol (0.1 mM) or CCCP (0.2 microM). Digitonin fractionation of the mitochondria into mitoplasts, outer membranes and an intermembrane fraction show that reduction of 35SO4(2-) to form free cysteine and cysteine of protein is located on the mitoplasts; adenosine 5'-phosphosulphate sulphotransferase, the first enzyme of sulphate reduction, is found in the same location. Sulphate activation is highly enriched in the mitochondrial fraction of Euglena; the small amount found in the chloroplast fraction can be attributed to mitochondrial contamination. Thus, in Euglena, sulphate activation and reduction are contained in a sulphate metabolizing centre on the outside of the mitochondrial inner membrane; this centre appears to supply the mitochondrion and the rest of the cell with the products of sulphate activation as well as with reduced sulphur in the form of cysteine. Mitochondria from wild-type Euglena cells and from W10BSmL, a mutant lacking plastids completely, appear to be similar in the properties studied.

Effect of heat shock on the mutagenicity of mutagens and carcinogens in Euglena gracilis

The effect of heat-shock treatment (42 degrees C for 15 min) on the ability of four mutagens and carcinogens to induce hereditary bleaching in Euglena gracilis cells was investigated. All four mutagens (treatment time: 1-24 h) tested after heat shock increased the frequency of bleached mutants of Euglena gracilis.

Enzymatic conversion of glutamate to delta-aminolevulinic acid in soluble extracts of Euglena gracilis

Glutamate was converted to the chlorophyll and heme precursor delta-aminolevulinic acid in soluble extracts of Euglena gracilis. delta-Aminolevulinic acid-forming activity depended on the presence of native enzyme, glutamate, ATP, Mg2+, NADPH or NADH, and RNA. The requirement for reduced pyridine nucleotide was observed only if, prior to incubation, the enzyme extract was filtered through activated carbon to remove firmly bound reductant. Dithiothreitol was also required for activity after carbon treatment. delta-Aminolevulinic acid formation was stimulated by RNA from various plant tissues and algal cells, including greening barley leaves and members of the algal groups Chlorophyta (Chlorella vulgaris, Chlamydomonas reinhardtii), Rhodophyta (Cyanidium caldarium), Cyanophyta (Anacystis nidulans, Synechocystis sp. PCC 6803), and Prochlorophyta (Prochlorothrix hollandica), but not by RNA derived from Escherichia coli, yeast, wheat germ, bovine liver, and Methanobacterium thermoautotrophicum. E. coli glutamate-specific tRNA was inhibitory. Several of the RNAs that did not stimulate delta-aminolevulinic acid formation nevertheless became acylated when incubated with glutamate in the presence of Euglena enzyme extract. RNA extracted from nongreen dark-grown wild-type Euglena cells was about half as stimulatory as that from chlorophyllous light-grown cells, and RNA from aplastidic mutant cells stimulated only slightly. delta-Aminolevulinic acid-forming enzyme activity was present in extracts of light-grown wild-type cells, but undetectable in extracts of aplastidic mutant and dark-grown wild-type cells. Gabaculine inhibited delta-aminolevulinic acid formation at submicromolar concentration. Heme inhibited 50% at 25 microM, but protoporphyrin IX, Mg-protoporphyrin IX, and protochlorophyllide inhibited only slightly at this concentration.

E. coli ribosomes with a C912 to U base change in the 16S rRNA are streptomycin resistant

Resistance to streptomycin (Sm) of Euglena gracilis chloroplasts can be due to a single C to T transition of the 16S rRNA gene in an invariant position which is equivalent to C912 of the Escherichia coli 16S rRNA. Since Euglena chloroplasts cannot be transformed we introduced, by site-directed mutagenesis, a C912 to T transition in the cloned rrnB operon (pKK3535) of E. coli and used this new construct (pEM109) in transformation experiments. Transformed E. coli cells were selected for Sm resistance by colony plating and stepwise increase of Sm up to 25 micrograms/ml of culture medium. Several Sm-resistant colonies were obtained. Ribosomes were isolated from pEM109-transformed Sm-resistant and pKK3535-transformed Sm-sensitive cells. The ribosomes were assayed in vitro for Sm-induced misreading of poly(U) mRNA. We isolated 16S rRNA and sequenced the crucial RNA region by reverse transcription. The results clearly show that ribosomes from Sm-resistant cells correctly read the poly(U) mRNA in the presence of 25 micrograms Sm/ml of reaction mixture and the 16S rRNA contains the C912 to U transition. We conclude that C912 is involved in a translation step(s) which is (are) sensitive to streptomycin.

Euglena gracilis chromatin: comparison of effects of zinc, iron, magnesium, or manganese deficiency and cold shock

The effects induced by Fe, Mn, or Mg deficiency or cold shock on the DNA content and histones of Euglena gracilis have been examined and compared to those produced by Zn deficiency. The DNA content of the stationary-phase organisms used as controls is 2.1 micrograms/10(6) cells. The DNA of stationary-phase iron-deficient (-Fe), magnesium-deficient (-Mg), manganese-deficient (-Mn), zinc-deficient (-Zn), and cold-shocked (CS) cells is increased to 3.0, 4.6, 6.2, 3.8, and 3.8 micrograms/10(6) cells, respectively. The electrophoretic mobilities of proteins solubilized with 0.4 N H2SO4 from CS, -Fe, -Mg, and -Mn cells are nearly identical and are characteristic of the five histone classes, H1, H2A, H2B, H3, and H4. In contrast, no histones are found in the equivalent acid extract from -Zn cells. The effect of micrococcal nuclease on chromatin from control, CS, and -Zn cells was examined. The chromatin of CS cells is 1.2-fold while that from -Zn cells is 10-30-fold more resistant to micrococcal nuclease digestion than is the chromatin of control cells. Thus, the chromatin of cells grown in Zn-deficient conditions differs markedly from that of organisms cultured in media deficient in Fe, Mn, or Mg or exposed to cold shock.

Benzothiazolium salts--relationships between their structure, toxicity and effect on the plastid system of Euglena gracilis

The effects of 41 benzothiazolium salts on Euglena gracilis were characterized with regard to the influence on growth and on chlorophyll synthesis, and to their ability to induce permanent loss of chloroplasts. Some salts induced white mutants of E. gracilis (the first benzothiazole derivatives with this activity). The relationship between the biological effect and chemical structure was confirmed and expressed quantitatively by means of Free - Wilson and Fujita - Ban analysis.

Localization of a sulphate-activating system within Euglena mitochondria

Intact mitochondria, obtained from Euglena gracilis Klebs var. bacillaris Cori mutant W10BSmL, which lacks plastids, and purified on Percoll density gradients, form adenosine 3'-phosphate 5'-phosphosulphate from sulphate. The optimal conditions include addition of 17 mM-Tricine/KOH, pH 7.6, 18 mM-MgCl2, 250 mM-sucrose, 5.66 mM-sodium ADP (or 0.94 mM-sodium ATP), 1 mM-K2SO4, carrier-free 35SO4(2-) (32.1 microCi) and 1.0 mg of mitochondrial protein in a total volume of 2.65 ml and incubation at 30 degrees C. Experiments with the inhibitor of adenylate kinase P1, P5-di(adenosine 5'-)pentaphosphate indicate that ATP is the preferred substrate for sulphate activation; ADP is utilized by conversion into ATP via adenylate kinase. ATP sulphurylase, adenylylsulphate kinase (APS kinase) and inorganic pyrophosphatase constitute the sulphate-activating system; ADP sulphurylase is undetectable. Fractionation of Euglena mitochondria with digitonin and centrifugation allowed the separation of outer-membrane vesicles and mitoplasts as judged by electron microscopy and selected enzymic markers. The detergent-labile association of the sulphate-activating system with the mitoplasts (similar to that of adenylate kinase), the fact that most of the adenosine 3'-phosphate 5'-phosphosulphate formed by intact mitochondria is found in the surrounding medium, and the ease with which nucleotide substrates reach the activating system in intact organelles, suggest that the enzymes of sulphate activation are located on the outer surface of the mitochondrial inner membrane.

Streptomycin-resistance of Euglena gracilis chloroplasts: identification of a point mutation in the 16S rRNA gene in an invariant position

We sequenced the chloroplast 16S rRNA gene of two Euglena gracilis mutants which contain streptomycin-resistant chloroplasts (Smr 139.12/4 and Smr 139.20/2). These mutants are known to contain a single intact rrn operon per circular chloroplast genome. Nucleotide sequence comparison between a 16S rRNA gene of wild type Euglena gracilis, strain Z, with streptomycin-sensitive chloroplasts, and the 16S rRNA gene of both Smr-strains reveals a single base change (C to T) at position 876. This position is equivalent to the invariant position 912 of the E. coli 16S rRNA gene. The analogous position is also conserved in all chloroplast small subunit RNA genes from lower and higher plants sequenced so far. Light dependent protein synthesis with purified chloroplasts from streptomycin-resistant cells is not inhibited by streptomycin. Based on the results reported here we postulate linkage between the observed point mutation on the 16S rRNA gene and streptomycin-resistance of chloroplast 70S ribosomes.

Hyperthermia and other factors increasing sensitivity of Euglena to mutagens and carcinogens

The effects of different factors (temperature, light, enzymic activation) on the ability of selected mutagens and carcinogens to induce hereditary bleaching of Euglena gracilis were investigated. In the resting medium, the elevation of incubation temperature from 25 degrees C to 37 degrees C increased significantly the effect of all compounds tested on the frequency of bleached mutants of E. gracilis. The effect of light is not so unambiguous. While nitrosoguanidine (NG) exhibited practically the same bleaching activity both in the light and dark, the mutagenic effect of sodium azide (SA), nitrovin (NV), nitrosoethylurea (NEU), and benzo(a)pyrene (BP) was decreased in light. On the other hand, the light increased the bleaching activity of 5-nitro-2-furylacrylic acid (NFAA) significantly. The activation mixture S9 increased bleaching effect of NFAA and BP, whereas other mutagens were partially (NG and SA) or completely (NV and NEU) inactivated.

Phallotoxin-visualization of F-actin in normal and chromium-poisoned Euglena cells

The presence of F-actin in Euglena cells was revealed by the use of fluorescent delta-aminophalloin. In normal cells F-actin forms a web of fine filaments at the cell periphery and around the nucleus. In Cr-poisoned cells this pattern is completely altered, and F-actin is visible as a single strongly fluorescent band of various shape and location.

Regulation of cell shape in Euglena gracilis. II. The effects of altered extra- and intracellular Ca2+ concentrations and the effect of calmodulin antagonists

When cultures of Euglena gracilis Z., normally grown in medium containing 180 microM-Ca2+, are resuspended in Ca2+-free medium cells assume round shapes within 10 min, from which they recover slowly when Ca2+ is returned to the cultures. Cultures grown in 10 microM-Ca2+ do not display the typical circadian rhythm in cell shape even though the photosynthesis and cell division circadian rhythms are unaffected. Elevating intracellular Ca2+ levels by the addition of the Ca2+ ionophore A23187 prevents cells from undergoing the two daily shape changes characteristic of growth-synchronized cultures, but does not alter the ability to maintain the cell shapes found at the time of ionophore addition. When the calmodulin inhibitors trifluoperazine or chlorpromazine are added to cultures, the cells always respond by rounding. Cells are not able to maintain any cell shape other than spherical in the presence of these inhibitors and therefore cannot change shape throughout the daily cycle as is found in the control populations.

Histone formation, gene expression, and zinc deficiency in Euglena gracilis

Histones, and other basic proteins, have been isolated from zinc-sufficient (+Zn) Euglena gracilis by standard chromatographic methods. These cells contain 2.46 micrograms of histones and 1.96 micrograms of DNA per 10(6) organisms. Each of the histones, H1, H3, H2A, H2B, and H4, is present in both log- and stationary-phase +Zn cells and has been characterized according to its electrophoretic mobility and molecular weight. H1 has been further identified on the basis of its amino acid composition and its cross-reactivity with calf thymus histone H1 antibodies. Similarly, H3 has been recognized as well by its specific reaction with an H3 antibody. In contrast, log-phase zinc-deficient (-Zn) cells contain H1 and H3 while H2A, H2B, and H4 are absent. All of the histones vanish in stationary-phase-Zn organisms. The DNA content increases as the -Zn cells progress from log to stationary phase, reaching a value of 4.40 micrograms/10(6) cells, double that of comparable stationary-phase +Zn organisms. A 2000-3000-dalton polypeptide whose electrophoretic behavior differs from that of the known histones constitutes over 90% of the total basic proteins of -Zn cells. On addition of zinc to stationary -Zn cells, cell division resumes, and all the histones and other basic proteins reappear. Together with previous results, the data demonstrate that zinc significantly affects the metabolism of all major chromatin components, i.e., the RNA polymerases, DNA, and histones of E. gracilis [Vallee, B.L., & Falchuk, K.H. (1981) Philos. Trans. R. Soc. London, Ser. B 294, 185-197]. The implications of these effects of zinc on chromatin structure and function are discussed.

Cytoplasmic regulation of chloroplast translation in Euglena gracilis

A regulatory role for cytoplasmically derived proteins in chloroplast translation in organello was examined by analyzing protein synthesis in plastids isolated from cells of Euglena gracilis which had been treated with cycloheximide (CHI). Incorporation of [35S]methionine by chloroplasts from CHI-inhibited Euglena was reduced approximately 40 and 90% by exposure of the cells to the antibiotic for 2 and 4 h, respectively. The chloroplast translation products were then analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and fluorography. The synthesis of polypeptides in the soluble compartment of the plastid was substantially diminished by as little as 15 min of CHI pretreatment. No qualitative alterations of the polypeptide pattern were detected. Qualitative changes were seen in the thylakoid fraction, however. Comparison of the stainable polypeptides and fluorographs of thylakoid membranes from CHI-treated cells with those of controls showed several instances in which the more slowly migrating member of a doublet accumulated with a concomitant depletion of a more rapidly migrating component. A pair of polypeptides at 28 and 30 kDa, which we believe are the Euglena homologs of the photogene product and its precursor, respectively, are representative of this phenomenon. Additionally, thylakoids from cells pretreated with CHI sometimes synthesized novel polypeptides larger than 65 kDa. Finally, when intact chloroplasts from CHI-inhibited Euglena were incubated with a postchloroplast supernatant from normal cells, there was a partial reversion of the anomalies seen in the fluorographs. These data are interpreted to indicate the cytoplasmic origin of one or more proteins whose function is to process chloroplast translation products.

The effects of tumor sera on cell shape and photosynthesis of Euglena gracilis

Cells of Euglena gracilis treated with human sera show a marked change in cell shape: Fully elongated cells have nearly totally been transformed to disk-shaped cells. This serum-mediated contraction is followed by irreversible cytolysis. Disintegration of chloroplast membranes leads to decreased photosynthetic O2 evolution. Sera from humans suffering from tumors reveal higher lytic activities than sera from individuals not suffering from tumors. Heating sera at 56 degrees C for 10 min or addition of EDTA destroyed or inhibited, respectively, the lytic activities completely. Polysaccharides transformed in polyanions by sulphatisation like dextransulphates or heparin seem to protect Euglena against serum activities. The effects described for human sera are believed to display the role of the complement pathway in the cytolysis of Euglena gracilis.

[Action of actinomycin D on Euglena gracilis ultrastructure]

Effects of 1 and 10 mkg/ml concentrations of actinomycin D, an inhibitor of RNA synthesis, on the ultrastructure of a phytoflagellate Euglena gracilis were followed during 48 hours. Similar changes were observed with both the concentrations, but the effect of the higher dose appeared in a short time and was more expressed. The effect of actinomycin D becomes obvious as early as half an hour after its adding; the cell nucleus, chloroplasts and mitochondria show definite responses. Chromatin condensation is seen in the nucleus, the nucleolus is enlarged in size, compressed and fragmented. Chloroplasts react to the action of actinomycin D by swelling, accumulation of osmiophilic globuli, disorganization and reduction of lamellar systems, formation of the myelin figures and gran-like structures and by the decomposition of pyrenoid. The mitochondrial matrix is compressed, the structure and orientation of the cristae become abnormal, and some electron-dense bodies appear.

[Action of the unsaponifiable components of the most common edible oils on the growth of the alga Euglena gracilis. Preliminary studies]

Within the sphere of the researches the biological effects of the most common edible oils (peanuts, sunflower, maize, soya and rectified olive) it has been studied the interaction between the development of the Euglena gracilis unicellular seaweed and the presence of the unsaponifiables examined in their cultures. As a biologically active substance it has been used 3,4-benzopyrene. Spectrophotometric analysis have evidenced that all the unsaponifiables, especially those of the soya seeds, caused a growth decrease of the seaweed culture. A similar effect is found in the cultures treated with aromatic hydrocarbon.

Radioassay for cobalamin (vitamin B12) requiring no pretreatment of serum

We describe a radioassay for cobalamin (vitamin B12) in human serum or plasma that requires no boiling or other pretreatment of the sample. Normal chicken serum covalently coupled to magnetizable particles is used as the binding agent. The assay is performed at pH 12.9, at which pH all cobalamin in human serum is released from its binding proteins, whereas the binding agent maintains a high affinity for cobalamin (Ka 1.7 x 10(10) L/mol). Under these assay conditions the binding protein shows a specificity for cobalamin similar to that of purified intrinsic factor. The assay is simple, rapid, and precise, and results correlate well with those of the Euglena gracilis microbiological assay and an intrinsic-factor binding assay.

Effects of erythromycin on Euglena gracilis as a model for testing the toxicity of antibacterial drugs

Based on the main physiological and ultrastructural effects induced in Euglena gracilis by erythromycin, one of the least toxic of the commonly used antibiotics that specifically inhibit protein synthesis on 70S ribosomes of prokaryotic organisms, a symptomatologic picture is outlined which could be useful for the preliminary evaluation of the toxicity of antibacterial agents.

Effect of diflubenzuron and its major degradation products on the growth of Euglena gracilis Z. and incorporation of glycine-U-14C in protein

Diflubenzuron (I) and its major degradation products 4-chlorophenyl urea (II), 2,6-difluorobenzoic acid (III) and 4-chloroaniline (IV) were tested for their activity on Euglena gracilis Z. The inhibition on the growth and on the incorporation of glycine-U-14C in the protein of Euglena was measured in the presence of I-IV ranging 10 to 200 ppm. 4-chloroaniline caused a considerable inhibition at every tested level whereas I-III slightly affected only the incorporation. Therefore, it must be inferred that diflubenzuron shows no effect on growth and protein biosynthesis for this nontarget organism.

Purification of Euglena gracilis chloroplast elongation factor G and comparison with other prokaryotic and eukaryotic translocases

Euglena gracilis chloroplast protein synthesis elongation factor G (EF-Gchl) has been purified to about 80% homogeneity by a two-step procedure which removes all traces of the cytoplasmic and mitochondrial translocases (EF-2 and EF-Gmt). The purification scheme generally results in approximately 130-fold purification with 20% recovery of the total EF-G activity present in whole cell extracts. The Euglena EF-Gchl is a monomeric protein with a molecular weight of approximately 85,000. As observed for all translocases to date, the activity of Euglena EF-Gchl is inhibited by treatment with low concentrations of N-ethylmaleimide, suggesting that a free sulfhydryl group is required for catalytic activity. Treatment with 3 microM fusidic acid results in a 50% inhibition of Euglena EF-Gchl activity and of the EF-G activity present in Chlamydomonas reinhardtii. About 10-fold higher concentrations of this antibiotic are required to inhibit the mitochondrial EF-G of Euglena and Escherichia coli EF-G to the same extent. Yeast mitochondrial EF-G is clearly distinguishable from the other organellar translocases tested, requiring 1 mM fusidic acid for 50% inhibition. Fusidic acid also inhibits the cytoplasmic translocases from yeast, wheat germ, and Euglena, although a wide range of sensitivities is observed. When antiserum raised against highly purified Euglena EF-Gchl is used to inhibit enzymatic translocation, a low degree of cross-reaction of the antiserum with Chlamydomonas EF-G and with E. coli EF-G is observed. The EF-G activity present in spinach is very slightly inhibited by the antiserum, whereas that of yeast is not affected. The mitochondrial and cytoplasmic translocases of Euglena are also unaffected by the antiserum against EF-Gchl. The evolutionary implications of these observations are discussed.

Effect of some benzthiazol derivatives on Euglena gracilis

6-Substituted derivatives of 2-benzthiazolthiol and allyl (2-benzthiazolylthio)acetate exhibit, after an exposure to light, and inhibitory action on the division of dark-depigmented Euglena cells, as well as the synthesis of chlorophyll. These substances also have a marked inhibitory effect on the devlopment of plastids in nondividing cells maintained under resting conditions. No induction of heterotrophic plastid--free mutants was found under growth or resting conditions.

Effects of Mg2+ and Ca2+ on photoinduced Euglena flagellar responses

The flagellar frequency and waveform of Euglena were analyzed under full illumination (420-700 nm) and in a restricted wavelength band (530-700 nm) when the cells were in a medium containing Mg2+ or had been microinjected with Mg2+, Mn2+, or Ca2+ in solution. Magnesium abolished the change in flagellar frequency and the reversal in waveform that cells exhibit when illuminated by a 530-700 nm wavelength band. Under this restricted illumination, Ca2+ caused an increase in flagellar waveform reversal and a decrease in beating frequency. The flagellar motility of cells impaled on a microelectrode was examined in cells illuminated with various wavelengths.

[Analyses of histones and of nucleosomal DNA of normal and vitamin B 12 starved Euglena]

An extraction and electrophoresis of histones from normal and starved Euglena cell nuclei allows us to show the presence of five types of histones in the two cases but a lower degree of acetylation appears in H4 histone from starved cells. It was shown that DNA repeat length from the two kinds of chromatin is comparable (225 b.p.).

Chlorophyll photobleaching and ethane production in dichlorophenyldimethylurea- (DCMU) or paraquat-treated Euglena gracilis cells

Light dependent (35 Klux) chlorophyll bleaching in autotrophically grown Euglena gracilis cells at slightly acidic pH (6.5-5.4) is stimulated by the photosystem II blockers DCMU and DBMIB (both 10(-5) M) as well as by the autooxidizable photosystem I electron acceptor, paraquat (10(-3) M). Chlorophyll photobleaching is accompanied by the formation of thiobarbituric acid -- sensitive material ("malondialdehyde") and ethane. Both chlorophyll photobleaching and light dependent ethane formation are partially prevented by higher concentrations (10(-4) M) of the autooxidizable photosystem II electron acceptor DBMIB or by sodium bicarbonate (25 mM). In vitro studies with cell free extracts (homogenates) from E. gracilis suggest that alpha-linolenic acid oxidation by excited (reaction center II) chlorophyll represents the driving force for both ethane formation and chlorophyll bleaching. Ethane formation thus appears to be a sensitive and non-destructive "in vivo" marker for both restricted energy dissipation in photosystem II and, conditions yielding reactive oxygen species at the reducing side of photosystem I.

Photosensory transduction in the flagellated alga, Euglena gracilis I. Action of divalent cations, Ca2+ antagonists and Ca2+ ionophore on motility and photobehavior

1. The flagellated alga, Euglena gracilis, swims forward essentially in a straight path under constant light intensity. Strong motility of the cells can be supported by Mg2+ alone but optimum motility is found in the presence of Mg2+, Ca2+ and K+. 2. Ca2+, Co2+, Mn2+ and Ba2+ induce a concentration-dependent increase in the rate at which the cells change the direction of their swimming path (a klinokinesis). Ni2+ immobilizes the flagellum. 3. On perception of a reduction ('step-down stimulus') in blue light intensity in their environment, Euglena rotate in place (tumble) for a finite period (the step-down photophobic response). 4. The duration of the tumbling is enhanced in the presence of divalent cations following the series Ca2+ greater than Ba2+ greater than Mn2+ greater than Co2+ greater than Mg2+ = Ni2+ = 0. 5. Neither the tumbling response in the presence of low concentrations of Ca2+ or the Ca2+-stimulated response is altered by verapamil (a Ca2+ conductance antagonist). The Ca2+ conductance/active transport antagonist, ruthenium red, is also inactive. 6. The Ca2+ ionophore, A23187, has little effect on flagellar activity in the absence of extracellular Ca2+. However, in the presence of A23187, Ca2+ induces a specific light-independent, concentration-dependent discontinuous tumbling response of the cells. 7. The data support a role for Ca2+ and Mg2+ in control of flagellar activity. However, blue light-induced tumbling behavior would not appear to be the direct result of a light-mediated alteration in the Ca2+ conductance of the flagellar membrane to affect flagellar reorientation. The results are discussed in connection with previous theories on control of flagella activity in green alga.

[Effect of external environmental factors on DNA content in Euglena]

The chromosome number and DNA content in Euglena gracilis cell have been shown by the number of investigators to vary essentially under the influence of some environmental factors (low phosphate and acetate concentrations, density of culture, temperature, light/dark regime, streptomycin treatment). Variability in the nuclear DNA quantity is supposed to be an important peculiarity of the structure and functional activity of the genome of Euglena gracilis.

Recovery from vitamin B-12-induced unbalanced growth. The shortened cell cycle and the deoxyribonucleoside triphosphate pools

The deoxyribonucleoside triphosphate pools are undetectable in vitamin B-12-deficient cells of Euglena gracillis, but appear rapidly after the replenishment with the vitamin. They reach a maximum size that is about 6 times that of normal exponentially growing cells, but decrease to almost zero as the cells divide. The pools expand again during the post-replenishment shortened cell cycle. However, the expansion takes place during rather than before the resumption of DNA synthesis. The maximum sizes reached are still larger than in normal cells. By using the protein-synthesis inhibitor cycloheximide and determining the pool size, we found that vitamin-deficient cells apparently accumulate a large amount of ribonucleoside triphosphate reductase apoenzyme, which lacks the vitamin B12 coenzyme. We showed that the production of the deoxyribonucleoside triphosphates is not closely coupled to DNA synthesis under our experimental conditions, and that the concentration of the deoxyribonucleoside triphosphate pools per unit of DNA synthesized is almost constant for all stages of growth examined.

Zinc biochemistry in normal and neoplastic growth processes

Zinc is essential for the growth of all species. Growth arrest results from its deficiency and presumably reflects important roles for this metal at critical points of metabolism. Studies of zinc metalloenzymes show that zinc serves as a coenzyme to more than 80 enzymes, among which are the reverse transcriptases which cause leukemia in many species. Its role in nucleic acid metabolism is emphasized.

Growth and cell volume of Euglena gracilis in different media

It is necessary to propagate Euglena gracilis cells for several days after transfer from one medium to another to establish the steady state of balanced growth. Steady-state growth was established in minimal and in complex medium. Specific growth rates and cell volume distributions were computed for each culture medium. Mean cell volume of E. gracilis is not uniquely correlated with the specific growth rate.

Effect of streptomycin on the structure and function of the photoreceptor apparatus of Euglena gracilis

The progressive modification of the photoreceptor apparatus, induced by addition of streptomycin (SM) to cultures of dark-bleached Euglena, is correlated with the change of the photomotor response. One of the effects of drug-treatment is the reduction of carotenoid synthesis; the total carotenoid content decreases from 0.20 to 0.01 pg/cell after seven weeks of treatment. The parallel progressive reduction of the stigma vesicles and their carotenoid content is observed by electron microscopy. Micrographs and microscopic fluorescence observations do not indicate alterations of the paraflagellar body (PFB). During the SM-treatment the initial positive phototactic response decreases until it disappears after five weeks. The loss of the absorbing properties of the stigma prevents the cell from orienting itself towards the light. The probability that the cell orients seems to depend on the light modulation amplitude and the light/dark ratio on the PFB due to the shading device. After seven weeks of SM-treatment we observe a cell movement away from the illuminated zone. The mechanism of this escape is discussed.