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1.
When Chlorella vulgaris llh cells which had been grown in airenriched with 2–4% CO2 (high-CO2 cells) were bubbled withair containing ca. 400 ppm CO2, illumination at an intensityas low as the light compensation point (350 lux) was sufficientto increase the photosynthetic rate under limiting CO2 concentrations.The same treatment induced carbonic anhydrase (CA) activity.The induction of CA activity and increase in photosyntheticrate at limiting CO2 concentrations were observed in the presenceof 10 µM DCMU which completely inhibits photosynthesis.These results indicate that photosynthetic electron transportis not involved in CA induction in Chlorella vulgaris llh cells.The parallelism between the changes in CA activity and the rateof photosynthesis under limiting CO2 concentrations agree withthe previous conclusion that the transport of CO2 from outsideto the site of CO2 fixation is facilitated by CA and hence lowersthe apparent Km(CO2) for photosynthesis. (Received December 24, 1982; Accepted May 10, 1983)  相似文献   

2.
Transfer of algal cells of Chlorella regularis from 3% CO2 inair into ordinary air in the light increased external carbonicanhydrase (CA) activity as well as photosynthetic affinity forCO2 by several-fold within 2 h. Since no noticeable differencewas observed in CA activity between intact cells and cell homogenates,CA seemed to be mainly localized on the cell surface. Changesin CA activity and K?(CO2) of photosynthesis were not observedin the dark. CA induction was 50%-inhibited by incubation with10 µM DCMU during adaptation of high-CO2 cells to air,whereas it was considerably suppressed when high-CO2 cells preincubatedwith DCMU in the light for 6 h or without DCMU in the dark for24 h were used. The change in K?(CO2) of photosynthesis wasonly slightly affected by DCMU. Uncoupler like carbonylcyanide-m-chlorophenyl-hydrazone(CCCP) and inhibitors of mitochondrial respiration (KCN plussalicylhydroxamic acid) suppressed CA induction during adaptationof high-CO2 cells to low CO2 conditions. These results suggest that photosynthesis is not essential forCA induction in Chlorella regularis when some amounts of photosyntheticproducts are previously stored in the cells and respirationis active. A decrease in K?(CO2) of photosynthesis during adaptationfrom high to low CO2 was mostly independent on photosynthesis.However, light is essential for both phenomena. (Received July 16, 1990; Accepted January 21, 1991)  相似文献   

3.
The maximum rate of photosynthetic 14CO2 fixation (Vmax) aswell as the concentration of CO2 at which the rate of photosynthetic14CO2 fixation attains one-half its maximum velocity (Km) inChlorella vulgaris 11h cells was strongly dependent on the concentrationof CO2 continuously provided during the algal growth. The Vmax (µmoles 14CO2 fixed/ml pcv?min) and Km (% CO2)of the algal cells which had been grown in air containing 4%CO2 (by volume) were ca. 10 and 0.15–0.17, while thosein the cells which had been grown in ordinary air (containing0.04% CO2) were 7 and 0.05–0.06, respectively. When the concentration of CO2 in the bubbling gas was loweredfrom 4 to 0.04% during the algal growth, their photosynthetickinetics attained the respective lower steady levels after 5–10hr. On the other hand, when the photosynthetic kinetics weredetermined 24 hr after raising the concentration of CO2 from0.04 to 4%, the Vmax and Km-values were found to have alreadyattained the respective higher levels. (Received October 15, 1976; )  相似文献   

4.
Rates of CO2 and HCC3 fixation in cells of various Chlorellaspecies in suspension were compared from the amounts of 14Cfixed during the 5 s after the injection of a solution containingonly 14CO2 or H14CO3. Results indicated that irrespectiveof the CO2 concentration during growth, Chlorella vulgaris 11h and C. miniata mainly utilized CO2, whereas C. vulgaris C-3,C. sp. K. and C. ellipsoidea took up HCO3 in additionto CO2. Cells of C. pyrenoidosa that had been grown with 1.5%CO2 (high-CO2 cells) mainly utilized CO2, whereas those grownwith air (low-CO2 cells) utilized HCO3 in addition toCO2. Cells that utilized HCO3 had carbonic anhydrase(CA) on their surfaces. The effects of Diamox and CA on the rates of CO2 and HCO3fixation are in accord with the inference that HCO3 wasutilized after conversion to CO2 via the CA located on the cellsurface. CA was found in both the soluble and insoluble fractions;the CA on the cell surface was insoluble. Independent of the modes of utilization, the apparent Km (NaHCO3)for photosynthesis was much lower in low-CO2 cells than in high-CO2ones. The fact that the CA in the soluble fraction in C. vulgarisC-3 was closely correlated with the Km(NaHCO3) indicates thatsoluble CA lowers the Km. 1 Dedicated to the late Professor Joji Ashida, one of the foundersand first president of the Japanese Society of Plant Physiologists. 4 On leave from Research and Production Laboratory of Algology,Bulgarian Academy of Sciences, Sofia. (Received September 14, 1982; Accepted March 1, 1983)  相似文献   

5.
The ratio of the extracellular to the intracellular activityof carbonic anhydrase (CA) in cells of Chlorella ellipsoideaC-27, adapted to low levels of CO2 for 24 h (low-CO2 cells),was about one to one. Treatment of intact cells with PronaseP inactivated about one-half of the extracellular CA activitywithout affecting photosynthetic activity. The CA activity incell homogenates and in cell-wall ghosts liberated during celldivision was completely inactivated by the same treatment. Pretreatmentwith Glycosidase mix, Chitosanase and Macerozyme enhanced theinactivation of the CA activity in intact cells. These resultssuggest that extracellular CA is evenly distributed throughoutthe whole cell-wall region. The apparent K1/2 for dissolved inorganic carbon (DIC) in low-CO2cells doubled when extracellular CA was inactivated by treatmentwith Pronase P, but the K1/2 obtained was still one-half ofthat in high-CO2 cells. Photosynthetic 14CO2-fixation in low-CO2cells was enhanced by acetazolamide, whereas H14CO3-fixationwas suppressed. The results suggest that CO2 is a dominant substrateutilized by cells and that HCO3 is utilized after conversionto CO2. The present results show that both intracellular andextracellular CA contribute to the increase in affinity forDIC during photosynthesis in low-CO2 cells of Chlorella ellipsoideaC-27. (Received May 7, 1990; Accepted July 18, 1990)  相似文献   

6.
Increases in carbonic anhydrase activity and decreases in K1/2(CO)2for photosynthesis in Chlorella vulgaris llh, which are inducedby adaptation of cells to low CO2, were suppressed by the additionof glucose to the growth medium. The results show that phenomenainduced by decreases in CO2 are controlled by glucose or itsmetabolites. (Received July 11, 1990; Accepted December 25, 1990)  相似文献   

7.
The affinity for NaHCO3 (CO2) in photosynthesis of Anabaenavariabilis ATCC 29413 was much higher in the cells grown underordinary air (low-CO2 cells) than in those grown in air enrichedwith 2–4% CO2 (high-CO2 cells) (pH 8.0, 25?C). Ethoxyzolamide(50 µM) increased the Km(NaHCO3 in low-CO2 cells aboutnine times (from 14.3 to 125), while the maximum rate of photosynthesisdecreased about 20%. When high-CO2 cells were transferred tolow-CO2 conditions, carbonic anhydrase (CA) activity increased,while Km(NaHCO3) in photosynthesis decreased from 140 to 30µM within about 5 h. The addition of CA to the suspensionof both high- and low-CO2 cells enhanced the rates of photosyntheticO2 evolution under CO2-limiting conditions. The rate of 14CO2fixation was much faster than that of H14CO3 fixation.The former reaction was greatly suppressed, while the latterwas enhanced by the addition of CA. These results indicate thatthe active species of inorganic carbon utilized for photosynthesiswas free CO2 irrespective of the CO2 concentration given duringgrowth. It is suggested that CA plays an active role in increasingthe affinity for CO2 in photosynthesis of low-CO2 cells of thisblue-green alga. (Received January 24, 1984; Accepted October 22, 1984)  相似文献   

8.
Chlorella vulgaris 11h cells grown in air enriched with 4% CO2(high-CO2 cells) had carbonic anhydrase (CA) activity whichwas 20 to 90 times lower than that of algal cells grown in ordinaryair (containing 0.04% CO2, low-CO2 cells). The CO2 concentrationduring growth did not affect either ribulose 1,5-bisphosphate(RuBP) carboxylase activity or its Km for CO2. When high-CO2 cells were transferred to low CO2 conditions,CA activity increased without a lag period, and this increasewas accompanied by an increase in the rate of photosynthetic14CO2 fixation under 14CO2-limiting conditions. On the otherhand, CA activity as well as the rate of photosynthetic 14CO2fixation at low 14CO2 concentrations decreased when low-CO2cells were transferred to high CO2 conditions. Diamox, an inhibitor of CA, at 0.1 mM did not affect photosynthesisof low-CO2 cells at high CO2 concentration (0.5%). Diamox inhibitedphotosynthesis only under low CO2 concentrations, and the lowerthe CO2 concentration, the greater was the inhibition. Consequently,the CO2 concentration at which the rate of photosynthesis attainedone-half its maximum rate (Km) greatly increased in the presenceof this inhibitor. When CO2 concentration was higher than 1%, the photosyntheticrate in low-CO2 cells decreased, while that in high-CO2 cellsincreased. Fractionation of the low-CO2 cells in non-aqueous medium bydensity showed that CA was fractionated in a manner similarto the distribution of chlorophyll and RuBP carboxylase. These observations indicate that CA enhances photosynthesisunder CO2-limiting conditions, but inhibits it at CO2 concentrationshigher than a certain level. The mechanism underlying the aboveregulatory functions of CA is discussed. 1This work was reported at the International Symposium on PhotosyntheticCO2-Assimilation and Photorespiration, Sofia, August, 1977 (18).Requests for reprints should be addressed to S. Miyachi, RadioisotopeCentre, University of Tokyo, Bunkyo-ku, Tokyo 113, Japan. (Received December 11, 1978; )  相似文献   

9.
Carbonic anhydrase (CA, EC. 4.2.1.1 [EC] ) activity in air-grown Characorallina was detected mainly in the intracellular fraction,most of which composed of chloroplasts and cytoplasmic gel,and not on the cell surface. Only minor levels of CA activity,on the basis of equivalent volumes, were detected in the cellsap and the cytoplasmic sol. The maximum rate of photosynthetic O2 evolution by air-grownChara corallina at pH 6.0 was twice that at pH 7.6, while theapparent Km for external inorganic carbon (Ci) at pH 7.6 wasabout three times that at pH 6.0. However, the apparent Km(CO2)was about three times larger at pH 6.0 than at pH 7.6. The Km(Ci)-valueat pH 7.6 increased severalfold in the presence of acetazolamide(AZA), an inhibitor of CA, but no inhibition was observed atpH 6.0. The pH-dependence may be due to differences in the permeabilityof AZA at the given pH values. Fixation of 14CO2 at 20 µMand of H14CO3 at 200 µM over the course of 5 swas very similar at pH 7.4. Addition of CA significantly suppressedthe photosynthetic 14CO2-fixation but it stimulated the H14CO3-fixation.This result indicates that free CO2 is an active species ofCi that is incorporated into the cell during photosynthesis. These results together suggest the following: (1) Free CO2 isutilized for photosynthesis, (2) CA is mainly located insidethe cell and functions to increase the affinity for CO2 in photosynthesisby facilitating the supply of CO2 from the plasmalemma to thesite of CO2-fixation. 3Present address: Biological Laboratory, The University of theAir, Wakaba 2-11, Chiba, 260 Japan. (Received December 9, 1988; Accepted March 22, 1989)  相似文献   

10.
The rate of photosynthetic 14CO2 fixation in Chlorella vulgaris11h cells in the presence of 0.55 mM NaH14CO3 at pH 8.0 (20?C)was greatly enhanced by the addition of carbonic anhydrase (CA).However, when air containing 400 ppm 14CO2 was bubbled throughthe algal suspension, the rate of 14CO2 fixation immediatelyafter the start of the bubbling was suppressed by CA. Theseeffects of CA were observed in cells which had been grown inair containing 2% CO2 (high-CO2 cells) as well as those grownin ordinary air (containing 0.04% CO2, low-CO2 cells). We thereforeconcluded that, irrespective of the CO2 concentration givento the algal cells during growth, the active species of inorganiccarbon absorbed by Chlorella cells is free CO2 and they cannotutilize bicarbonate. The effects observed in the high-CO2 cellswere much more pronounced than those in the high-CO2 cells.This difference was accounted for by the difference in the affinityfor CO2 in photosynthesis between the high- and low-CO2 cells. (Received May 19, 1978; )  相似文献   

11.
Increase of carbonic anhydrase activity was enhanced by decreasingthe O2 concentration when Chlorella vulgaris 11h cells grownunder 3% CO22 in ordinary air were transferred to low CO2 conditions.The carbonic anhydrase activity finally attained under the steadystate was dependent on the CO2 concentration, irrespective ofthe O2 concentration used. (Received April 24, 1988; Accepted February 23, 1988)  相似文献   

12.
The kinetic properties of ribulose 1,5-bisphosphate carboxylase(RuBPC) appear to have been modified during evolution of photosynthesisto adjust to changes in substrate availability. C4 plants areconsidered to have a higher concentration of CO2 available toRuBPC than C3plants. In this study, the Km(CO2 and catalyticcapacity (kcat) of RuBPC and the ratio of RuBPC protein to totalsoluble protein from several Flaveria species, including C3,C3-C4 intermediate, and C4 species, were determined. The C3and intermediate species had similar Km(CO2) values while theC4 species on average had higher Km(CO2) values. The mean ratioof Kcat/Km for species of each group was similar, supportingthe hypothesis that changes in Km and Kcat, are linked. Theallocation of total soluble protein to RuBPC was lowest in theC4 Flaveria species, intermediate in the C3-C4 species, andhighest in the C3 species. The results suggest that during evolutionof C4 photosynthesis adjustments may occur in the quantity ofRuBPC prior to changes in its kinetic properties. (Received January 4, 1989; Accepted April 11, 1989)  相似文献   

13.
Intracellular accumulation of inorganic carbon (Ci) and itsfixation in photosynthesis were investigated using siliconeoil layer filtering centrifugation technique with the cellsof Chlorella vulgaris 11h grown under ordinary air. Both CO2and HCO3 were transported into the cells from the reactionmedium and accumulated in the cells, but the rate of transportwas much faster for the former than the latter. 14C-fixationfrom the total transported Ci was much more efficient when CO2was added in the external medium than when HCO3 was added.This indicates that CO2 and HCO3 were not converted tothe common compound in the cells during the initial period ofphotosynthesis. Accumulation of Ci into the cells was much lesssusceptible to low temperature than its fixation. Accumulationof Ci was also observed in the dark. Ethoxyzolamide, an inhibitorof carbonic anhydrase (CA), inhibited the fixation of accumulatedCO2 in the cells, suggesting that CA enhanced the supply ofCO2 to the reaction site of ribulose bisphosphate carboxylasein the stroma. Mechanism for transport and fixation of Ci duringphotosynthesis in low-CO2 cells of C. vulgaris 1lh was proposedfrom these results. (Received March 19, 1986; Accepted June 26, 1986)  相似文献   

14.
Carbonic anhydrase (EC 4.2.1.1 [EC] ; CA) was purified by affinitychromatography from cells of the unicellular green alga Chlamydomonasreinhardtii which had been grown photoautotrophically in ordinaryair. Antiserum raised in rabbit against this purified CA crossreactedwith Chlamydomonas CA but not with spinach leaf CA nor bovineerythrocyte CA. When the CO2 concentration provided to the algalcells was decreased from 4% to the ordinary air level (0.04%),CA activity and the content of CA protein determined by theimmunodiffusion test showed parallel increases. In contrast,when the CO2 concentration was raised from air level to 4% CO2CA activity and its content expressed on the basis of culturevolume remained rather constant. These results indicate thatsynthesis of the CA protein is induced when the CO2 concentrationis lowered from 4 to 0.04% during algal growth. On the otherhand, the synthesis of CA stops when CO2 concentration is raisedfrom air level to 4%. (Received June 30, 1984; Accepted October 8, 1984)  相似文献   

15.
The carbon dioxide compensation point of the unicellular greenalga, Chloretla saccharophila, was determined in aqueous mediumby a gas chromatographic method. Compensation points decreasedmarkedly from 63 cm3 m–3 at an external pH of 4.0 to 3.2cm3 m–3 at pH 8.0 and were not affected by the O2 concentrationof the medium. The calculated CO2 concentration required tosupport the half-maximum photosynthetic rate of the algal cellsranged from 6.0 mmol m–3 at an external pH of 60 to 1.5mmol m–3 at pH 8.0 and these values were not affectedby O2 concentration. The Km(CO2) of nbulose-l,5-bisphosphatecarboxylase isolated from cells grown either at pH 4.0 or pH8.0 was determined to be 64 mmol m–3. These results indicatethat loss of CO2 by photorespiration does not occur in C. saccharophilacells at acid pH and the disparity between the apparent affinityfor CO2 of the intact cells and that of the carboxylase indicatesthe operation of a ‘CO2 concentrating mechanism’in this alga at acid pH. Key words: Acidophilic alga, bicarbonate transport, Chlorella saccharophila, compensation point, CO2 affinity, PH, RuBP carboxylase  相似文献   

16.
Photosynthetic carbon metabolism was studied with Chroomonassp. cells in which the rate of photosynthesis was inhibitedunder both an anaerobic condition and high concentrations ofoxygen. The time course of 14C-incorporation into photosyntheticproducts showed that 3-phosphoglycerate was the initial productof photosynthetic CO2 fixation in Chroomonas sp. cells. During5-min photosynthesis, a considerable amount of 14C was incorporatedinto the insoluble fraction (mostly cryptomonad starch), andoxygen predominantly affected 14C-incorporation into this fraction.Although 14C-incorporation into intermediates of the photorespiratorypathway increased with increasing O2 concentration, the amountswere much less than expected from the degree of oxygen inhibition.It is noteworthy that 14C-dihydroxyacetone phosphate accumulatedduring photosynthesis only under the anaerobic condition, whereasthe levels of the other phosphate esters were scarcely affectedby the oxygen concentration. Ribulose-1,5-bisphosphate carboxylase from Chroomonas sp. wascompetitively inhibited by oxygen, and its Km(CO2) value wassimilar to those of terrestrial C3 plant enzymes. (Received November 19, 1984; Accepted May 20, 1985)  相似文献   

17.
The acid-tolerant green alga Chlorella saccharophila maintainedphotosynthesis and accumulated intracellular pools of inorganiccarbon over a a range of external pH from 4.0 to 7.5. This accumulationwas unaffected by treatment of cells with 10 mol m–3 acetazolamide(AZA). Cells grown at alkaline pH had extracellular carbonicanhydrase (CA), but CA activity was repressed when cells weregrown at pH 5.0. Acid-grown cells retained a high affinity forCO2, both at acid and alkaline pH, and the ability to accumulateinorganic carbon. Rates of photosynthesis of acid-grown cellsand alkaline-grown AZA-treated cells at pH 8.0 were 2.5-foldhigher than the rate of CO2 supply from the uncatalysed dehydrationof , indicating that the cells can take up as a source of substrate for photosynthesis. Isotopic disequilibrium experiments with acid-grown cells maintainingsteady-state photosynthesis at pH 7.5 demonstrate that 14C from14CO2 was taken up more rapidly than from H14. This uptake takes place against a concentration gradient. Theseresults demonstrate that C. saccharophila cells have activetransport systems for the uptake of both CO2 and and both operate without the mediation of CA. Key words: Bicarbonate transport, carbon dioxide, carbonic anhydrase, Chlorella saccharophila, inorganic carbon accumulation  相似文献   

18.
Ribulose bisphosphate carboxylase (E.C.4.1.1.39) was purifiedfrom leaves of Triticum aestivum, Hordeum vulgare, Spinaceaoleracea, Petroselinum crispum, salad mustard-most likely Brassicanapus, Helianthus annuus, Solanum tuberosum, Beta vulgaris,Lolium perenne, Equisetum arvense, Zea mays, Ginkgo biloba,Pteris aquilina, Salix babylonica, Chamaecyparis lawsonianaand Atrichum undulatum by density gradient centrifugation andgel filtration or by ammonium sulphate fractionation, densitygradient centrifugation, ion-exchange chromatography and gelfiltration. Purified enzymes were freeze-dried and then storedat 0 °C to 4 °C. Portions of each enzyme preparationwere reactivated at 25 °C for 5 h in the presence of 10mM HCO2 and 20 mM MgCl2-RuBP carboxylase activities were measuredat four different concentrations of CO2 at 25 °C and pH8.2 in solutions equilibrated with pure nitrogen or air (21%O2, 79% N2). Km(CO2), Vmax and K1(O2) values were computed fromthe results. Significant differences were found in the Km(CO2)values for enzymes isolated from different species. Sensitivityof the enzymes to oxygen was less variable.  相似文献   

19.
In situ light measurements were used to obtain information oninherent and apparent optical properties. The average verticalattenuation coefficient Kd(ave) varied from 1.1 to 4.6 In unitsm–1 During three periods the variation in Kd(ave) correlatedwith changes in chlorophyll a concentration and specific attenuationcoefficients Ks, of 0.013, 0.014 and 0.022 m2 mg Chl a–1were calculated. Chlorophyll-specific diffuse absorption coefficients(A,) for these periods were 0.012. 0.013 and 0.017 m2 mg Chla–1 and only varied significantly from estimates of Ksin the period when scattering was intense. Absorption coefficientsa(zmid) and scattering coefficients b(zmid) calculated for themid-point of the euphotic zone ranged between 0.45 and 2.9 mand 3.5–52.0 m respectively. Chlorophyll-specific absorptioncoefficients Ka, of 0.005, 0.006 and 0.007 m2 mg Chl a–1and scattering coefficients Kb of 0.05. 0.09 and 0.191 m2 mgChl a–1 were measured during the three periods. The highKb value occurred when gas-vacuolate cyanobactena were dominant.Algal photosynthesis and light absorption were related throughthe maximum quantum yield m which varied between 0.019 and 0.11mol C Einstein–1 while average quantum yields a, variedbetween 0.006 and 0.024 with a mean of 0.013 mol C Einstein–1A comparison of changes in the mean irradiance of the mixedzone and chlorophyll concentration indicated that growth waslight limited below 0.04–0.05 Einsteins absorbed mg Chla–1 day–1.  相似文献   

20.
The utilization of inorganic carbon and role of the coccolithswere investigated in intact cells and protoplasts of a marineunicellular calcareous alga, Emiliania huxleyi. Protoplastswith high photosynthetic activity were obtained by artificialdecalcification with 50 mM MES-NaOH (pH5.5). (1) The kineticsof the photosynthetic evolution of O2 at various concentrationsof externally added NaHCO3 were the same for intact cells andprotoplasts, indicating that the kinetic properties with respectto dissolved inorganic carbon (DIC) were not affected by thepresence or absence of the coccoliths on the cell surface. Double-reciprocalplots and plots of the concentration of substrate divided byvelocity (s/v) against the concentration of substrate (s) werebiphasic in the case of both intact cells and protoplasts. TheCO2-utilization reaction was, therefore, considered to involvetwo processes with different values of Km and Vmax. From thekinetic analyses, Km and Vmax [µmoles O2 (ml PCV)–1h–1] were deduced to be 92 µM and 76.3 for a "low-Km"reaction and 4.1 mM and 252 for a "high-Km" reaction, respectively.(2) In short-term (40-min) experiments, time courses of thetotal uptake of 14C-DIC and the incorporation of 14C into acid-stableproducts of photosynthesis and the internal pool of DIC, determinedas acid-labile compounds, under CO2-limiting conditions (80µM) were very similar for intact cells and protoplasts.However, incorporation of 14C into CaCO3 apparently occurredmore slowly in protoplasts than in intact cells. (3) In longterm (24-h) experiments, patterns of incorporation of 14C werealmost same for intact cells and protoplasts, with the exceptionthat the amount of 14C incorporated into CaCO3 was much smallerin the former than the latter. The production of Ca14CO3 increasedduring the course of 10 h after a 4-h lag. However, after 10h the level of Ca14CCO3 started to decrease. The decrease wasaccompanied by an increase in 14C in the products of photosynthesis,suggesting that CaCO3 was reutilized for the photosyntheticfixation of CO2 and, therefore, that the coccoliths functionas sites of storage of DIC. However, the internal level of DICremained at the same level even after the supply of externalDIC has been almost completely depleted. (Received July 25, 1995; Accepted December 11, 1995)  相似文献   

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