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PubMed2006

Expression switching of three genes encoding light-independent protochlorophyllide oxidoreductase in Chlorella protothecoides.

Three chloroplast genes, chlL, chlN and chlB, encoding the light-independent protochlorophyllide oxidoreductase (LIPOR) in Chlorella protothecoides CS-41 growing either photoautotrophically, mixotrophically or heterotrophically, were all transcribed constitutively independent of illumination and presence of glucose. Steady-state amounts of all three transcripts in the light-grown cells were, however, approximately two- to three-fold greater than those in the dark-grown cells. In addition, Western blotting demonstrated that approximately the same amount of protein was present in cultures grown mixtrophically or heterotrophically both containing glucose. However, much less protein was in photoautotrophic cells. These results suggest that LIPOR activity depends on post-transcriptional and post-translational regulation. Moreover, the fact that LIPOR accumulates in the light-grown cells indicates that LIPOR, which was thought to work only in darkness, may partially account for the protochlorophyllide photoreduction in light. Therefore, LIPOR switches on both in light and in darkness.

Chlorella↗
PubMed2006

Production of deuterated lutein by Chlorella protothecoides and its detection by mass spectrometric methods.

Chlorella protothecoides, a lutein-producing microalga, was grown aerobically in a mineral medium prepared with 70% (v/v) deuterated water. HPLC/atmospheric pressure chemical ionization-mass spectrometry (HPLC/APCI-MS) analysis revealed approximately 58% replacement of hydrogen by deuterium atoms as indicated by the molecular mass cluster at around m/z 599. The rapidly growing microalga had much higher levels (58%) of deuterium substitution relative to previously reported (9-15%) natural sources of lutein.

Chlorella↗
PubMed2026

Microalgae-Mediated Synthesis of Gold Nanoparticles from Indonesian Chlorella vulgaris InaCC M205 with Potential Anticancer Properties for Biomedical Application.

Sustainable nanomaterial synthesis has emerged as a critical strategy to reduce the environmental burden associated with conventional chemical synthesis method. Microalgae-derived biomolecules offer a promising platform for the green production of metal nanoparticles due to their rich bioactive compounds capable of acting as natural reducing and stabilizing agents. Here, we report the eco-friendly synthesis of gold nanoparticles (AuNPs) using extract of Indonesian microalga Chlorella vulgaris extract. To optimize the synthesis process, the effects of precursor-to-extract ratio, temperature, and incubation time were evaluated. Optimal synthesis of C5-AuNPs was obtained at 37 °C for 20 h with precursor to extract ratio of 6:4, resulting in moderately stable C5-AuNPs characterized by a surface plasmon resonance (SPR) peak at 541 nm. Furthermore, Fourier-transmission infra-red (FT-IR) analysis revealed the involvement of functional groups of C. vulgaris extract in the interaction with Au+ during the production of C5-AuNPs. Transmission electron microscopy (TEM) demonstrated the formation of uniformly spherical nanoparticles with an average diameter of approximately 8.8 nm. Biological evaluation showed that the synthesized C5-AuNPs exerted pronounced dose-dependent cytotoxicity against MCF-7 breast cancer cells with an IC50 threshold of 21.17 ppm, while no toxicity appears in normal HEK293 cells. Mechanistically, the C5-AuNPs induced early apoptosis and inhibit cell-cycle progression at the stage of G0/G1. Collectively, these findings demonstrate that C. vulgaris-mediated AuNPs represent a promising preliminary in vitro findings for cancer therapy candidate.

Gold↗
PubMed1988

Exclusion chromatography with controlled-pore glass beads to isolate Chlorella chromatin and its applications.

A simple and rapid method was developed to isolate chromatin from the unicellular alga, Chlorella, by exclusion chromatography utilizing controlled-pore glass beads. This method takes advantage of the giant size of the chromatin supramolecules and does not require the preliminary isolation of cell nuclei. In order to raise the histone yield, commercially available materials were silanized with dimethyldichlorosilane. The isolated algal chromatin had properties similar to those of other organisms, and the histones contained all five components found in calf thymus. A hierarchy of the higher order structures was also observed in the algal chromatin. This method can be used for the study of chromatin in various cell types, especially in microbial cells, from the viewpoints of not only mere preparation but also cell dynamics and fractionation in relation to the specific components or activities. Some application examples are presented.

Cell Cycle↗
PubMed1983

Positive correlation between superoxide dismutase and resistance to paraquat toxicity in the green alga Chlorella sorokiniana.

Paraquat (10-30 microM) exerted a dose-dependent and light-dependent toxicity on Chlorella sorokiniana. Paraquat was also seen to increase the superoxide dismutase content of these cells and to cause the appearance of a new electrophoretically distinct isozyme. Cells grown in the absence of paraquat contained one manganese-superoxide dismutase and two iron-superoxide dismutases, while the paraquat-grown cells contained an additional manganese-superoxide dismutase. Cells which were grown in the presence of 25 microM Paraquat, and which therefore possessed elevated levels of superoxide dismutase, were resistant to 30 microM Paraquat, whereas control cells were bleached and killed by this level of Paraquat. Electron micrography and chemical analysis revealed that Paraquat decreased the starch content of the cells and caused a failure of dividing cells to separate. It appears that Paraquat increases the photoproduction of O2- in C. sorokiniana and that an increase in the cell content of superoxide dismutase is an adaptive response which provides protection against this herbicide.

Cell Division↗
PubMed1984

Superoxide dismutase and chilling injury in Chlorella ellipsoidea.

The relationship between superoxide dismutase (SOD) and chilling injury was examined in chilling-sensitive and chilling-resistant strains of Chlorella ellipsoidea. The sensitive strain contained less SOD than the resistant strain. Moreover, all of the SOD in the sensitive strain was the H2O2-sensitive, iron-containing SOD, whereas most of the SOD in the resistant strain was the H2O2-resistant, manganese-containing SOD. Illumination further enhanced the disparity in SOD content between the sensitive and resistant strains since the SOD in the former declined during illumination, whereas the SOD in the latter strain did not. It was possible to elevate the SOD content of the sensitive strain and to increase the proportion of MnSOD by prior growth in the presence of 50 microM paraquat. The SOD content of the cultures after 5 h of illumination at 4 degrees C fell in the order sensitive strain less than paraquat-induced sensitive strain less than resistant strain. The resistance of these cultures to chilling injury was related to SOD content. This was the case whether resistance was assessed in terms of growth rate after chilling, bleaching of chlorophyll during chilling, or loss of viability during chilling. It thus appears likely that O2- is an agent of chilling injury.

Adaptation, Biological↗
PubMed1985

Enzymatic conversion of glutamate to delta-aminolevulinate in soluble extracts of the unicellular green alga, Chlorella vulgaris.

Cell-free preparations from the unicellular green alga, Chlorella vulgaris, catalyze the conversion of glutamate to delta-aminolevulinate, which is the first committed step in heme and chlorophyll biosynthesis. Most activity remains in the supernatant fraction after centrifugation at 264,000g. Additional activity can be solubilized from the high-speed pellet by treatment with 0.5 M NaCl. After gel filtration through Sephadex G-25, the reaction catalyzed by the high-speed supernatant requires glutamate, ATP, Mg2+, and NADPH. Boiled extract is inactive. The pH optimum is between 7.8 and 7.9 and the temperature optimum is 30 degrees C. Concentrations required for half-maximal activity are 0.05 mM glutamate, 0.4 mM ATP, 6 mM MgCl2, and 0.4 mM NADPH or 0.7 mM NADH. The reaction requires no additional amino donor. Involvement of pyridoxal phosphate in the catalytic mechanism is suggested by sensitivity to pyridoxal antagonists; 50% inhibition is achieved with 5 microM gabaculine or 0.4 mM aminooxyacetate. Involvement of two or more enzymes is suggested by the nonlinear reaction rate dependence on protein concentration. Evidence for the involvement of an activated glutamate intermediate was obtained by product formation after sequential addition and removal of substrates, and by inhibition (80%) with 1 mM hydroxylamine. Protoheme inhibits the activity by 50% at 1.2 microM. Preincubation of the extract with ATP causes stimulation and/or stabilization of the activity compared to preincubation without ATP or no preincubation. In preparations obtained from C. vulgaris strain C-10, which requires light for greening, dark-grown cells yield one-third as much activity as 4-h-greened cells.

Adenosine Triphosphate↗
PubMed1985

RNA is required for enzymatic conversion of glutamate to delta-aminolevulinate by extracts of Chlorella vulgaris.

Formation of delta-aminolevulinic acid (ALA) from glutamete catalyzed by a soluble extract from the unicellular green alga, Chlorella vulgaris, was abolished after incubation of the cell extract with bovine pancreatic ribonuclease A (RNase). Cell extract was prepared for the ALA formation assay by high-speed centrifugation and gel-filtration through Sephadex G-25 to remove insoluble and endogenous low-molecular-weight components. RNA hydrolysis products did not affect ALA formation, and RNase did not affect the ability of ATP and NADPH to serve as reaction substrates, indicating that the effect of RNase cannot be attributed to degradation of reaction substrates or transformation of a substrate or cofactor into an inhibitor. The effect of RNase was blocked by prior addition of placental RNase inhibitor (RNasin) to the cell extract, but RNasin did not reverse the effect of prior incubation of the cell extract with RNase, indicating that RNase does not act by degrading a component generated during the ALA-forming reaction, but instead degrades an essential component already present in active cell extract at the time the ALA-forming reaction is initiated. After inactivation of the cell extract by incubation with RNase, followed by administration of RNasin to block further RNase action, ALA-forming activity could be restored to a higher level than originally present by addition of a C. vulgaris tRNA-containing fraction isolated from an active ALA-forming preparation by phenol extraction and DEAE-cellulose chromatography. Baker's yeast tRNA, wheat germ tRNA, Escherichia coli tRNA, and E. coli tRNAglu type II were unable to reconstitute ALA-forming activity in RNase-treated cell extract, even though the cell extract was capable of catalyzing the charging of some of these RNAs with glutamate.

Adenosine Triphosphate↗
PubMed1989

Induction and synthesis of nitrate reductase in Chlorella vulgaris.

Assimilatory nitrate reductase is an inducible, eukaryotic enzyme that responds to a variety of environmental cues. When higher plants and green algae are grown with ammonia as a nitrogen source, low levels of nitrate reductase activity are present. Transfer to nitrate-containing medium is accompanied by substantial increase of nitrate reductase activity. Here it is shown immunologically that, in the green algae Chlorella vulgaris, nitrate reductase protein is over-produced as activity appears during induction. Immunoreactive protein is also found in cells grown on ammonia. Low levels of translatable mRNA for nitrate reductase are present in ammonia-grown cells. These data suggest that: (i) nitrate reductase appearance is controlled primarily on a transcriptional level, but that transcription is not completely halted under repressing conditions; (ii) there is an overproduction of nitrate reductase protein early during the induction period as previously suggested; and (iii) nascent protein, from in vitro translation, is of approximately the same molecular size as the nitrate reductase subunit and therefore little posttranslational modification is necessary to generate the functional enzyme. Insertion of cofactors and assembly are probably the only post-translational events.

Chlorella↗
PubMed1975

Reactions between primary and secondary acceptors of photosystem II in Chlorella pyrenoidosa under anaerobic conditions as studied by chlorophyll fluorescence.

The kinetics of the fluorescence yield phi of chlorophyll a in Chlorella pyrenoidosa were studied under anaerobic conditions in the time range from 50 mus to several minutes after short (t 1/2 = 30 ns or 5 mus) saturating flashes. The fluorescence yield "in the dark" increased from phi = 1 at the beginning to phi approximately 5 in about 3 h when single flashes separated by dark intervals of about 3 min were given. After one saturating flash, phi increased to a maximum value (4-5) at 50 mus, then phi decreased to about 3 with a half time of about 10 ms and to the initial value with a half time of about 2 s. When two flashes separated by 0.2 s were given, the first phase of the decrease after the second flash occurred within 2 ms. After one flash given at high initial fluorescence yield, the 10-ms decay was followed by a 10 s increase to the initial value. After the two flashes 0.2 s apart, the rapid decay was not followed by a slow increase. These and other experiments provided additional evidence for and extend an earlier hypothesis concerning the acceptor complex of Photosystem II (Bouges-Bocquet, B. (1973) Biochim. Biophys. Acta 314, 250-256; Velthuys, B. R. and Amesz. J. (1974) Biochim. Biophys. Acta 333, 85-94): reaction center 2 contains an acceptor complex QR consisting of an electron-transferring primary acceptor molecule Q, and a secondary electron acceptor R, which can accept two electrons in succession, but transfers two electrons simultaneously to a molecule of the tertiary acceptor pool, containing plastoquinone (A). Furthermore, the kinetics indicate that 2 reactions centers of System I, excited by a short flash, cooperate directly or indirectly in oxidizing a plastohydroquinone molecule (A2-). If initially all components between photoreaction 1 and 2 are in the reduced state the following sequence of reactions occurs after a flash has oxidised A2- via System I: Q-R2- + A leads to Q-R + A2- leads to QR- + A2-. During anaerobiosis two slow reactions manifest themselves: the reduction of R (and A) within 1 s, presumably by an endogenous electron donor D1, and the reduction of Q in about 10 s when R is in the state R- and A in the state A2-. An endogenous electron donor, D2, and Q- complete in reducing the photooxidized donor complex of System II in reactions with half times of the order of 1 s.

Anaerobiosis↗
PubMed1975

Inhibition of oxygen evolution following illumination of Chlorella cells with far-red light.

The effect of brief far-red illumination on Chlorella pyrenoidosa cells has been investigated. An inhibition of oxygen evolution occurs 20 to 30 s after the end of the far-red illumination. This inhibition occurs in a step following the initial charge separation process by the System II centers. It is reversible in the light through a purely photochemical process.

Chlorella↗
PubMed1976

Correlation between flash-induced oxygen evolution and fluorescence yield kinetics in the 0 to 16 mus range in Chlorella pyyrenoidosa during incubation with hydroxylamine.

Following flash excitation, oxygen pulses and fluorescence kinetics in the time range 0-16 mus were studied in the alga Chlorella pyrenoidosa during incubation with various concentrations of hydroxylamine. The obtained results could be explained considering four effects of hydroxylamine. 1. Hydroxylamine removes (reduces) oxidizing equivalents, generated in the water-splitting system by flash excitation. This process does not markedly affect the fluorescence yield kinetics between 0 and 16 mus following the ignition of a flash and reaches a constant rate within a few minutes, but possibly within a few seconds, after addition of hydroxylamine. In a sequence of flashes separated by dark time td, the steady-state oxygen yield in the flashes is exp(-ktd), the yield at td=0 being taken equal to 1, where k=(0.1 + beta[NH2OH])s-1, with [NH2OH] in mM and beta=0.6 mM-1, provided [NH2OH]greater than or equal to 0.5 mM. 2. An inhibition between Z, the physiological donor and the oxidized reaction center pigment P+ occurs, proceeding as exp (-kiti)where ti is the incubation time with hydroxylamine and ki=(alpha[NH2OH]) min-1, with [NH2OH] in mM and alpha=0.14 mM-1. This process not only inhibits oxygen evolution capability, but also decreases the amplitude of the fluorescence yield difference deltaphi=phi(16 mus)-phi(2 mus) induced by a flesh in the steady state. In a fraction of the reaction centers this inhibition occurs "immediately" after the addition of hydroxylamine. These observations, combined with the conslusion of Cheniae and Martin (1971, Plant Physiol. 47, 568-575) that the inhibition of the Hill reaction is related to the extraction of bound manganese indicate that the reaction between Z and P+ requires bound manganese. 3. In the inhibited centers a second donor for P+, D, connected to an entry site for the artificial electron donor hydroxylamine becomes apparent. 4. A flash-induced oxygen uptake signal was observed in the presence of hydroxylamine, which was shown to be caused by a system II reaction. The effects under (1) and (4) were reversed in the dark if hydroxylamine was removed by washing. The effects under (2) and (3) were reversed during illumination of a washed sample.

Chlorella↗
PubMed1976

Enhancement studies on algae and isolated chloroplasts. Part I. Variability of photosynthetic enhancement in Chlorella pyrenoidosa.

Studies of the variability of enhancement in Chlorella pyrenoidosa confirm the existence of two types of variability: a very slow diurnal variation linked to the growth cycle and a much more rapid adaptive response to the immediate incident light conditions (State I-State II transitions). Measurements of the wavelength dependencies and relative contributions of these two types of variability suggest that they may be linked. A close examination of the enhancement signals associated with the State I-State II transition reveals that the transitions can take place in any one of three ways: by a change in Photosystem II efficiency alone, by a change in Photosystem I efficiency alone or by a simultaneous change in the efficiencies of both photo systems. Measurements of the rates of transition between State I, State II and the dark adapted state, Dark, suggest that the behaviour of State II and Dark are normally, but not always, identical. The transitions between the three states were found to be first order. For those samples exhibiting the same behaviour in Dark and State II, the rate of the State I-State II transition was found to be independent of the wavelength of Light II, suggesting that the return from State I to State II is essentially a dark process and that the driving force for the adaptive transition is the over-stimulation of Photosystem I. Finally, a model is proposed, involving an antagonistic control of the quantum yields of photochemistry of the two photosystems, that is capable of explaining the links between the two types of variability, their wavelength dependencies and the shapes of the individual enhancement signals.

Chlorella↗
PubMed1976

Fluorescence lifetimes of Chlorella pyrenoidosa.

The flucrescence decay of Chlorella pyrenoidosa has been investigated under a variety of conditions in the picosecond and nanosecond time regions. Most of the fluorescence is accounted for by an expression of the form I(t) = I0exp-(At+Bt1/2) though an additional exponential term is required to include a weak component of lifetime 32 ps observable only at the higher pulse intensities. This interpretation reconciles earlier and apparently conflicting data. The weak 32 ps component may be associated with Photosystem I, although the possibility that it is an artefact of the high intensity pulses used cannot be excluded at present. The main fluorescence, described by the equation above is attributed to the antenna chlorophyll and is of the form which would be expected from a single light harvesting array with trapping at randomly distributed sites.

Chlorella↗
PubMed1977

515 nm Absorption changes in Chlorella at short times (4--100 mus) after a flash.

Using Chlorella, three types of absorption changes at 515 nm have been studied in the 4-100 mus time range following a flash. (1) The absorption change observed when both photoreactions are blocked, probably due to the formation of the triplet state of a carotenoid, is show to depend on Photosystem II excitation only. (2) The absorption increase induced by photoreaction I is biphasic; first phase, complete in less than 4 mus, followed by a slower phase with a half-rise time of 15-20 mus. (3) On the other hand, photoreaction II induces only a fast absorption increase (lessthan 4 mus). The time course of the biphasic 515 nm absorption increase induced by photoreaction I is similar to the biphasic absorption decrease previously observed at 480 nm by Cox and Delosme (1976, C.R. Acad. Sci. Paris 282D, 775-778). No significant absorption change is observed at 490 nm. These results suggest that the transmembrane electric field induced by photoreaction I rises to its maximum value in at least two phases within 100 mus following flash excitation.

Chlorella↗
PubMed1977

Cytochrome f and plastocyanin kinetics in Chlorella pyrenoidosa. I. Oxidation kinetics after a flash.

P-700, plastocyanin and cytochrome f redox kinetics were measured after one flash, using dark-adapted Chlorella in the presence of hydroxylamine and 3(3,4-dichlorophenyl)-1,1-dimethylurea. Plastocyanin becomes increasingly oxidized with a half-time of 70 microseconds, then undergoes reduction with a half-time of 7ms. Cytochrome f oxidation has a sigmoidal time-course and a half-time of 100 microseconds. Its redution exhibits a half-time of 4 ms. These results are interpreted in a linear scheme: (formula: see text). An equilibrium constant of 2 between cytochrome f and plastocyanin (PC), which contrasts with the large equilibrium constant between PC and P-700 is computed. The presence of cytochrome b6 in a cyclic path around Photosystem I is confirmed under these conditions.

Chlorella↗
PubMed1977

Cytochrome f and plastocyanin kinetics in Chlorella pyrenoidosa. II. Reduction kinetics and electric field increase in the 10 ms range.

On dark-adapted Chlorella, after one flash, plastocyanin (PC) undergoes reduction with a half-time of 7 ms. After 4 or 5 flashes, the reduction of PC+ in the 10 ms range is suppressed, and the level of oxidized plastocyanin increases during the next few flashes before reaching a stationary value. Cytochrome f exhibits approximately the same pattern. The reduction of PC+ and cytochrome f+ in the 10 ms range is correlated with an increase of the electrice field named phase b (Joliot, P. and Delosme, R., Biochim. Biophys. Acta 357 (1974) 267-284). Both need the presence of a compound R' in the reduced state. A dark electron transfer involving a carrier of electrons across the membrane, a proton carrier, R' as terminal reducant, PC+ and cytochrome f+ as terminal oxidants, would account for this field generation. Cooperation between the electron transfer chains is implied at the level of plastocyanin oxidation. An equilibrium constant of about 2 is observed between cytochrome f and plastocyanin before 1 ms and after 500 ms after the photochemical reactions. We observe that cytochrome f and plastocyanin are not connected from 1 to 100 ms after a photochemical reaction. The equilibrium constant between plastocyanin and P-700 remains large [20] under these conditions.

Chlorella↗
PubMed1978

Kinetics of reduction of the oxidized primary electron donor of photosystem II in spinach chloroplasts and in Chlorella cells in the microsecond and nanosecond time ranges following flash excitation.

Absorption changes (deltaA) at 820 nm, following laser flash excitation of spinach chloroplasts and Chlorella cells, were studied in order to obtain information on the reduction time of the photooxidized primary donor of Photosystem II at physiological temperatures. In the microsecond time range the difference spectrum of deltaA between 750 and 900 nm represents a peak at 820 nm, attributable to a radical-cation of chlorophyll a. In untreated dark-adapted material the signal can be attributed solely to P+-700; it decays in a polyphasic manner with half-times of 17 microseconds, 210 microseconds and over 1 ms. The oxidized primary donor of Photosystem II (P+II) is not detected with a time resolution of 3 microseconds. After treatment with 3--10 mM hydroxylamine, which inhibits the donor side of Photosystem II, P+II is observed and decays biphasically (a major phase with t1/2=20--40 microseconds, and a minor phase with t1/2 congruent to 200 microseconds), probably by reduction by an accessory electron donor. In the nanosecond range, which was made accessible by a new fast-response flash photometer operating at 820 nm, it was found the P+II is reduced with a half-time of 25--45 ns in untreated dark-adapted chloroplasts. It is assumed that the normal secondary electron donor is responsible for this fast reduction.

Chlorella↗