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PubMed1979

Magnetic field-induced increase of the yield of (bacterio)chlorophyll emission of some photosynthetic bacteria and of Chlorella vulgaris.

In photosynthetic bacteria, in which the iron-ubiquinone complex X is prereduced, a magnetic field induces an increase of the emmission yield, which is correlated with the decrease in reaction center triplet yield reported previously (Hoff, A.J., Rademaker, H., van Grondelle, R. and Duysens, L.N.M. (1977) Biochim. Biophys. Acta 460, 547--554). Our results support the hypothesis that under these conditions charge recombination of the oxidized primary donor and the reduced primary acceptor predominantly generates the excited singlet state of the reaction center bacteriochlorophyll. In Chlorella vulgaris and spinach chloroplasts, at 120 K, the magnetic field has an effect similar to that found in bacteria, which suggests that an intermediary electron acceptor between P-680 and Q is present in Photosystem II also.

Bacteriochlorophylls↗
PubMed1979

A backflow of electrons around photosystem II in Chlorella cells.

A study was made with a modulated oxygen electrode of the effect of variations of oxygen concentration on photosynthetic oxygen evolution from algal cells. When Chlorella vulgaris is examined with a modulated 650 nm light at 22 degrees C, both the oxygen yield and the phase lag between the modulated oxygen signal and the light modulations have virtually constant values between 800 and 120 ergs . cm-1 . s-1 if the bathing medium is in equilibrium with the air. Similar results are obtained at 32 degrees C between 1600 and 120 ergs . cm-2 . s-1. Under anaerobic conditions both the oxygen yield and the phase lag decrease if the light intensity is lowered below about 500 ergs . cm-2 . s-1 at 22 degrees C or about 1000 ergs . cm-2 . s-1 at 32 degrees C. A modulated 706 nm beam also gives rise to these phenomena but only at significantly lower rates of oxygen evolution. The cells of Anacystis nidulans and Porphyridium cruentum appear to react in the same way to anaerobic conditions as C. vulgaris. An examination of possible mechanisms to explain these results was performed using a computer simulation of photosynthetic electron transport. The simulation suggests that a backflow of electrons from a redox pool between the Photosystems to the rate-limiting reaction between Photosystem II and the water-splitting act can cause a decrease in oxygen yield and phase lag. If the pool between the Photosystems is in a very reduced state a significant cyclic flow is expected, whereas if the pool is largely oxidized little or no cyclic flow should occur. It is shown that the effects of 706 nm illumination and removal of oxygen can be interpreted in accordance with these proposals. Since a partial inhibition of oxygen evolution by 3-(3.4-dichlorophenyl)-1,1-dimethylurea (10(-8) M) magnifies the decreases in oxygen yield and phase lag, it is proposed that the pool which cycles back electrons is in front of the site of 3-(3,4-dichlorophenyl)-1,1-dimethylurea inhibition and is probably the initial electron acceptor pool after Photosystem II.

Anaerobiosis↗
PubMed1979

Flash-induced scattering transients in the 10 microseconds--5 s time range between 450 and 540 nm with Chlorella cells.

Flash-induced transients in light scattering were shown to occur with Chlorella cells. The kinetic and spectral patterns of the scattering transients and their relation to the absorption changes studied in the 10 microseconds--5 s time range, between 450 and 540 nm. 1. The kinetics of the fast changes (less than 500 ms) in scattering and absorbance were identical. From about 500 ms divergence of the two signals was observed. 2. The transient spectrum characterizing the fast scattering changes exhibited a large double band between 480 and 500 nm. Transients corresponding to the slower changes resembled the steady scattering spectrum (Latimer, P. and Rabinowitch, E. (1959) Arch. Biochem. Biophys. 84, 428--441) with a maximum at about 515 nm. 3. From theoretical considerations it is suggested that fast transients in scattering and absorbance are physically interrelated, and as has been shown for absorption changes (Witt, H.T. (1971) Q. Rev. Biophys. 4, 365--477) fast scattering transients can also be interpreted as an electrochromic phenomenon. Slower changes are accounted for by alterations in the microenvironment and conformation of the particles responsible for scattering.

Chlorella↗
PubMed1979

Dichlorophenylurea-resistant oxygen evolution in Chlorella after cerulenin treatment.

Fluorescence spectra at 77 K, oxygen evolution at 30 degrees C and delayed fluorescence at 25 degrees C were measured in Chlorella pyrenoidosa cultures with and without cerulenin and subsequent 3-(3,4-dichlorophenyl)-1,1-dimethyl-urea (DCMU) treatment, respectively. In pure algal cultures the oxygen evolution was inhibited by DCMU and the long-time component of fluorescence was highly influenced by DCMU, as expected. In contrast, both oxygen evolution and delayed fluorescence became DCMU-resistant in cerulenin-treated cultures. The DCMU-resistance is correlated with a change in the fatty acid distribution of the thylakoid membrane, which also leads to changes in the prompt fluorescence. Cerulenin appears to be a promising new tool of diagnostics for the hitherto unsatisfactorily understood processes of oxygen evolution in photosynthesizing organisms.

Antifungal Agents↗
PubMed1980

Electron and proton transfers from P-430 to ferredoxin-NADP-reductase in Chlorella cells.

After blocking Photosystem II on whole Chlorella cells, we measured the absorption changes between 0 degrees C and -10 degrees C. The absorption changes measured 2 mus after the beginning of a Xenon Flash are the sum of changes due to P(+)-700 and changes due to P(-)-430 (after the subtraction of the carotenoid triplet change and of the electrochromic effect). The reduction of P(-)-430 is not resolved by our technique. Its reoxidation presents a half-time around 1 mus at 0 degrees C and around 2 mus at -10 degrees C. The reduction and protonation of ferredoxin-NADP-reductase to its neutral semi-quinoid form FNRH present a half-time of about 3 mus at 0 degrees C and 6 mus at -10 degrees C. The presence of only one photoreducible ferredoxin-NADP-reductase per Photosystem I center is confirmed, but is an acceptor X' the differential extinction coefficients of which are weak or null from 420 nm to 480 nm. Tentative explanations which would reconcile these results with what was already known about ferredoxin are proposed.

Chlorella↗
PubMed1980

Light intensity saturation properties of O2 yields in a sequence of flashes in Chlorella.

As a function of the light intensity of flash n in a sequence, the O2 yields Yn, Yn+1 and Yn+2 have been measured: n = 1, 2, 3 and 6 in the examples given. It is shown that: (1) No double hit exists in the first saturating flash in Chlorella. (2) the flash saturation curve of the O2 yield Yn+1 as a function of the intensity of flash n exhibits a small sigmoidal shape at weak light. (3) If Yn+1 is detected at different times after the flash n of variable intensity, a well developed lag distinguishes the saturation curve of the O2 yield measured a long time after flash n (200 ms) with respect to that measured at shorter time (300 microseconds). Nevertheless, a large amount of double hits with the transitions S1 leads to S3 cannot occur in each flash, because it would lead to a periodicity of three rather than four in the O2 yield pattern. The saturation curve of the transition S2* leads to S3 is different from the other S-state saturation curves which are close to an exponential function; even with a short flash (0.3 microseconds), this curve shows a small lag at low light intensity, and its saturation intensity is higher than that of the other transitions. The low quantum yield of the transition S2* leads to S3 at low flash light intensity is explained by a product, T, partially inhibiting the formation of S3; at higher intensity, the quantity of formed S2* being larger than that of available T, only a part of S2* is inhibited and the quantum yield is higher than at low intensity.

Chlorella↗
PubMed1980

Acid-induced double hits in glutaraldehyde-treated Chlorella.

Glutaraldehyde-treated Chlorella cells show pH-dependent oxygen evolution characteristics. 1. The oxygen yield on the second flash (Y2) of a sequence of 2 mus flashes is pH-dependent, the rest of the sequence is unchanged. 2. This yield on the second flash increases as the dark-time between sequences is increased. 3. The deactivation times for the S2 and S3 states are not significantly changed at different pH values. 4. Using a short flash (0.5 mus) for the first flash, no oxygen was detected on the second flash, indicating that there is no S2 remaining in the dark. 5. When the intensity of the first flash is varied, a sigmoidal curve is obtained for Y2 as a function of flash intensity of the first flash is varied, a sigmoidal curve is obtained for Y2 as a function of flash intensity at pH 6.0 but not at pH 7.5. This is indicative of a double hit process. 6. At pH 6.0 the turnover of the Photosystem II centers after the first flash has a fast rise (t 1/2 < 25 mus) followed by a slow phase. This behaviour is not seen at pH 7.5, nor after two flashes. 7. We propose a scheme in which an auxiliary acceptor is in series with Q1 and in competition with B. The redox potential of the auxiliary acceptor is pH dependent.

Aldehydes↗
PubMed1981

The effect of the uncoupler carbonyl cyanide m-chlorophenylhydrazone on K+ transport, ATP level and intracellular pH of Chlorella fusca.

1. Low concentrations of the uncoupler carbonyl cyanide m-chlorophenylhydrazone (CCCP) induced net K+ uptake by Chlorella fusca, optimal concentrations being 3 microM CCCP in the light and 1 microM CCCP in the dark. Higher concentrations increasingly stimulated K+ release. 2. Measurements of the unidirectional K+ fluxes showed that CCCP-induced net K+ uptake in the light was mainly a consequence of an inhibition of efflux. In the dark, influx was slightly stimulated in addition. 3. In conditions of CCCP-induced net K+ uptake, the ATP level was decreased by less than 10%. With higher CCCP concentrations it fell drastically. 4. By means of the 5,5-dimethyloxazolidine-2,4-dione distribution technique, an acidification of the cell interior on the addition of CCCP was found. 5. It is concluded that uncoupler-induced net K+ uptake is due to an enhanced proton leakage into the cell across the plasmalemma. Intracellular acidification by this process stimulates ATP-dependent K+/H+ exchange which, in itself, is not affected at low uncoupler concentrations.

Adenosine Triphosphate↗
PubMed1981

Vanadium in photosynthesis of Chlorella fusca and higher plants.

The influence of vanadium compounds (vanadate, vanadyl citrate) on photosynthesis in Chlorella fusca and in algal and spinach chloroplasts has been investigated. It was found that: 1. At moderately high concentrations (at least 0.1 mM) both vanadate and vanadyl citrate enhance photosynthetic O2 production in intact C. fusca cells. At lower V concentration (about 2 microM) only vanadate stimulates photosynthesis. The increase is dependent on culture conditions and on light intensity. 2. Up to 1 mM V, neither vanadium compound influences PS II activity, either in intact cells or in algal or spinach chloroplasts. 3. The PS I reaction in algal and spinach chloroplasts is maximally enhanced (3-fold) in presence of vanadium (20 microM). The increase is independent of light intensity. 4. Cr(VI), Mo(VI), and W(VI) (1 mM) stimulate photosynthesis in intact C. fusca cells, but do not influence the photosystems of isolated chloroplasts. Vanadium is suggested to act as a redox catalyst in the electron transport from PS II to PS I.

Chlorella↗
PubMed1993

The relationship between the capacity to evolve oxygen and the variable fluorescence of chlorophyll after microsecond illumination in Chlorella, pea leaves and pea thylakoids.

The relationship between the capacity to evolve oxygen following a flash of a few microseconds duration and the variable fluorescence of chlorophyll was determined in Chlorella, leaf disks of peas, and thylakoids of pea leaves. It was found that this relationship is linear in intact plant material, while it is nonlinear in thylakoids. However, in thylakoids, the recovery of the capacity to evolve oxygen does not track the decay of the variable yield of Chl a fluorescence. This nonlinear relationship in thylakoids results from a reduced rate in the oxygen evolution reaction with no change in the decay of the variable yield of Chl a fluorescence. From a new application of the matrix analysis method to oxygen flash yields, the S1'-->S2, S2'-->S3 and S3'-->S4-->S0 transitions are found to be slowed or delayed in pea thylakoids and this underlies the slower rate of the recovery of the capacity to evolve oxygen in thylakoids. It is concluded that in intact cells the QA-QB(-)-->QA QB- reaction was rate-limiting for the recovery of the capacity to evolve oxygen, the equal energy-transfer hypothesis and the sequential double-hit model are valid in pea leaves and that the apparent invalidity in thylakoids is actually due to slowing of reaction steps in the oxygen evolution mechanism.

Chlorella↗
PubMed1976

Different proton-sugar stoichiometries for the uptake of glucose analogues by Chlorella vulgaris. Evidence for sugar-dependent proton uptake without concomitant sugar uptake by the proton-sugar symport system.

The uptake of hexoses by Chlorella vulgaris is accompanied by the uptake of protons. For 6-deoxyglucose a stoichiometry of one proton taken up per sugar molecule has been measured, whereas for 1-deoxyglucose approximately two protons are taken up per sugar molecule. It was found that in the presence of 1-deoxyglucose a considerable proportion of "carrier" catalyzes the transport of protons without the concomitant transport of sugar. Presumably, the binding of sugar initiates the translocation of the carrier-proton-sugar complex, but whereas 1-deoxyglucose can still dissociate from the complex at the external side of the cytoplasmic membrane, the translocation of the carrier-proton complex continues. This conclusion was reached since (a) the composition of the translocated carrier-proton-sugar complex is the same for both sugar. Its formation is a first order reaction with respect to protons. (b) When 6-deoxyglucose, present inside cells, is exchanged for external sugar, the exchange ratio is two to one when the external sugar is 1-deoxyglucose, two molecules of 6-deoxyglucose are lost for each molecule of 1-deoxyglucose entering. This result indicates that during uptake of 1-deoxyglucose statistically only each second carrier molecule appearing at the internal side of the cytoplasmic membrane is carrying sugar.

Binding Sites↗
PubMed1979

The effect of intracellular pH on the rate of hexose uptake in Chlorella.

The rate of hexose uptake by Chlorella is reduced by uncouplers such as carbonyl cyanide p-trifluoromethoxyphenyl hydrazone or dinitrophenol even before concentration equilibrium is reached. The addition of uncouplers changes the membrane potential and the intracellular pH. The membrane potential does not influence the initial velocity of net sugar uptake, whereas manipulation of the cell pH by means of dimethyloxazolidinedione or by butyric acid uncovered a dramatic influence of cell pH on the rate of hexose uptake: at pH values of 7.5--6.8 maximal rate of uptake is observed but at more acid pH a strong inhibition takes place with virtually total blockage of uptake at pH 6.1. The decrease of cell pH to 6.1 in the presence of carbonyl cyanide p-trifluoromethoxyphenyl hydrazone could therefore account for the decrease in hexose transport rate. It was shown that the intracellular pH as such determines the rate of uptake and not the pH difference between inside and outside; the transport rate did not correlate with delta pH.

Biological Transport↗
PubMed1994

The HUP1 gene product of Chlorella kessleri: H+/glucose symport studied in vitro.

An in vitro system was established to measure secondary active transport mediated by plant H+ symporters. For this purpose plasma membranes of Schizosaccharomyces pombe cells transformed with the HUP1 gene coding for the H+/hexose symporter of Chlorella kessleri were fused with cytochrome-c oxidase containing proteoliposomes. After energization with ascorbate/TMPD/cytochrome c these vesicles built up a protonmotive force of > 130 mV consisting mainly of a membrane potential of > 100 mV (inside negative). Energized vesicles accumulated D-glucose in a pH-dependent way up to 30-fold which was not the case with control vesicles prepared from cells transformed with the plasmid not containing the HUP1 gene. The Km value for D-glucose uptake was 5 x 10(-5) M. The pH-dependence of accumulation was not due to a difference in protonmotive force, but reflected the pH-dependence of the carrier activity, i.e., the accumulation was determined by kinetic and by thermodynamic parameters. In the system both components of protonmotive force delta psi and delta pH can be manipulated individually, which allows to evaluate to what extent they contribute to sugar accumulation. The results indicate that under certain conditions the internal pH may be a limiting factor for D-glucose accumulation.

Chlorella↗
PubMed1977

Coordinate and non-coordinate accululation of aspartate transcarbamylase and dihydroorotase in synchronous Chlorella cells growing on different nitrogen sources.

Regulation of the levels of aspartate transcarbamylase (carbamoylphosphate:L-aspartate carbamoyltransferase, EC 2.1.3.2) and dihydroorotase (L-5,6-dihydro-orotate amidohydrolase, EC 3.5.2.3) was studied in synchronous cultures of the eucaryotic microorganism Chlorella. Analytical polyacrylamide gel electrophoresis and sucrose density-gradient centrifugation studies revealed that these cells contain a single aspartate transcarbamylase and a dihydroorotase with apparent molecular weights of 160 000 and 80 000, respectively. In synchronous cells cultured in nitrate medium, these two enzymes accumulated in single step-patterns over different periods of the cell cycle. In contrast, these enzymes accumulated in a coordinate manner throughout the cell cycle in ammonium medium. Experiments with inhibitors of protein and RNA synthesis indicated that dihydroorotase is stable in vivo and suggested that cell cycle changes in the turnover rate of aspartate transcarbamylase might determine whether or not these enzymes accumulate in a coordinate manner. Although uracil and uridine could be absorbed and metabolized by the cells, synthesis of these two enzymes could not be repressed by culturing synchronous cells in medium, containing high concentrations (29-40 mM) of uracil or uridine, for an entire cell cycle.

Amidohydrolases↗
PubMed1980

Purification by affinity chromatography and properties of uroporphyrinogen I synthetase from Chlorella regularis.

Uroporphyrinogen I synthetase (porphobilinogen ammonia-lyase (polymerizing), EC 4.3.1.8) from Chlorella regularis was purified to homogeneity by affinity chromatography on porphobilinogen-AH-Sepharose 4B, which was prepared by reacting carbodiimide with substrate, porphobilinogen. The enzyme was purified 232-fold from the initial crude extract and specific activity was 348 nmol porphyrinogen I formed (mg protein)-1 . h-1 at pH 7.4. The molecular weight of the enzyme was 35 000-36 000 as determined by Sephadex G-100 gel filtration. This enzyme was acidic protein having an isoelectric point of 4.2. The enzyme exhibited a single pH optimum at a pH value of 7.4 both in phosphate and Tris-HCl buffer. The Km value for porphobilinogen was 89 microM as measured by its consumption and 85 microM when uroporphyrin formation was used. The Arrhenius plot obtained from the enzyme activity measurements appeared triphasic with breaks occurring at 35 and 46 degrees C and activation energy was calculated to be 21 700 (10-35 degrees C), 12 700 (35-46 degrees C) and 1800 cal . mol-1 (46-65 degrees C). This enzyme was heat stable and the enzyme still retained 87% of activity, even after 1 h incubation at 75 degrees C.

Amino Acids↗
PubMed1996

The characterisation and cyclic production of a highly unsaturated homoserine lipid in Chlorella minutissima.

The marine alga Chlorella minutissima contains DGTS (diacylglyceryl-N,N,N-trimethylhomoserine) as a major component (up to 44% of total lipids). This lipid is absent from other members of the Chlorococcales, except for C. fusca, which contains DGTS as 1.3% of total lipids. Contrary to expectation, the DGTS is accompanied by PC (phosphatidylcholine) as the major phospholipid. DGTS is normally highly saturated in the C-1 position of glycerol, but in C. minutissima, both C-1 and C-2 are acylated with EPA (eicosapentaenoic acid, 20:5) in the major molecular species (over 90% of total). The DGTS level shows a marked rhythmic fluctuation with time which is inversely correlated with the level of MGDG (monogalactosyldiacylglycerol), the other major lipid. Improved NMR data and the first electrospray MS data on this lipid are presented.

Chlorella↗
PubMed1991

Differential regulation by trophic conditions of phosphorylating and non-phosphorylating NADP(+)-dependent glyceraldehyde-3-phosphate dehydrogenases in Chlorella fusca.

The two NADP(+)-dependent glyceraldehyde-3-phosphate dehydrogenases present in the green alga Chlorella fusca, namely, the phosphorylating (chloroplastic) enzyme and the non-phosphorylating (cytosolic) enzyme, are differently affected by the trophic conditions prevailing in the cell cultures. The addition of metabolizable sugars to cell cultures growing in the light promotes a marked decrease of the phosphorylating enzyme activity down to a barely detectable cellular level. In contrast, the cellular level of the non-phosphorylating enzyme is even enhanced in the presence of such sugars. These effects are not observed, however, with a number of non-assimilable sugar analogs. After sugar removal, a recovery of the phosphorylating activity--in a process which is inhibited by cycloheximide but not by lincomycin--is observed in illuminated cells but not in darkness, thus indicating a light-dependent nuclear synthesis of the chloroplastic enzyme. It seems therefore that the two dehydrogenases are adaptative enzymes subject to differential regulation by nutritional conditions.

Carbohydrates↗
PubMed1989

The hexose carrier from Chlorella. cDNA cloning of a eucaryotic H+-cotransporter.

The cDNA coding for the inducible H+/hexose cotransporter of Chlorella kessleri has been cloned and sequenced. It was isolated by differential screening of a cDNA library prepared from glucose-induced cells. The increase in expression of the gene correlates quantitatively with the increase in uptake activity due to induction; it is not expressed in a hexose transport mutant. An open reading frame allows for a membrane protein of 533 amino acids with a relative molecular mass of 57 kDa. This protein is highly homologous to the human and rat glucose transporters catalyzing facilitated diffusion and to the bacterial H+/pentose cotransporters. It is not related to the H+/lactose cotransporter of E. colli and to the mammalian Na+/glucose cotransporter.

Base Sequence↗