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1.
A sulfite-dependent ATPase [EC 3.6.1.3 [EC] ] of Thiobacillus thiooxidanswas activated and solubilized by treatment with trypsin [EC3.4.4.4 [EC] ], and purified 84-fold with a 32% recovery. It requiredboth Mg2+ and SO32– for full activity, and its optimumpH was found at 7.5–8.0. Mn2+, Co2+, and Ca2+ could partiallysubstitute for Mg2+, while SeO32– and CrO42– couldpartially substitute for SO32–. The enzyme hydrolyzed ATP and deoxy-ATP most rapidly and otherphosphate esters were poorer substrates. The apparent Km valuefor ATP was 0.33 mM. The enzyme activity was strongly inhibitedby 0.2 mM NaN3 and 10 mM NaF. (Received July 27, 1977; )  相似文献   

2.
Glutamate dehydrogenase (GDH) (EC 1.4.1.3 [EC] .) purified from greentobacco callus mitochondria was activated markedly by Ca2$ inthe amination reaction. This activation was detectable evenat concentrations below 5 µM Ca2$. Saturation curves for the three substrates of the aminationreaction showed normal Michaelis-Menten kinetics in the presenceof 1 mM of Ca2$, but pronounced substrate inhibition occurredwithout Ca2$. The effect of Ca2$ was chiefly on the maximalvelocity. The saturation curve for NH4Cl in the presence of Ca2$ was modulatedby a change in pH. The apparent Km value for NH4Cl markedlydecreased whereas that for -ketoglutarate increased slightlywhen the pH was raised from 7.3 to 9.0. In contrast, the Kmfor NADH was little affected by raising the pH. The characteristicof GDH which increases its affinity for NH4Cl when the pH israised may be compatible with the detoxification of ammonia. 1 Present address: Mochida Pharmaceutical Co., Ltd. (Received August 24, 1981; Accepted November 28, 1981)  相似文献   

3.
Changes in the metabolic activities of peroxide-producing systemsand peroxide-scavenging systems after freezing and thawing inflower buds of the apple, Malus pumila Mill., were studied withspecial reference to freezing injury. In flower buds of the‘McIntosh’ apple that were frozen below lethal temperatures,the activity of NADH-Cyt c reductase (EC 1.6.99.3 [EC] ), one of theenzymes in the electron-transport chains that are related tothe peroxide-producing systems, decreased slightly, while thatof Cyt c oxidase (EC 1.9.3.1 [EC] ) hardly changed. By contrast, theactivities of glucose-6-phosphate dehydrogenase (EC 1.1.1.49 [EC] ),dehydroascorbate reductase (EC 1.8.5.1 [EC] ) and ascorbate peroxidase(EC 1.11.1.11 [EC] ), which are involved in the peroxide-scavengingsystems, decreased to very low levels. The activity of glyceraldehyde-3-phosphatedehydrogenase (EC 1.2.1.12 [EC] ) also decreased markedly. However,little change was observed in the activities of hexokinase (EC2.7.1.1 [EC] ), glucosephosphate isomerase (EC 5.3.1.9 [EC] ), glutathionereductase (EC 1.6.4.2 [EC] ) and glutathione peroxidase (EC 1.11.1.9 [EC] ).Examination of substrates involved in the peroxide-scavengingsystems revealed that the levels of glucose-6-phosphate andfructoses-phosphate decreased to approximately 10–4 to10–5 M and 10–5 M, respectively, and the levelsof GSH decreased to about 10–5 M or became barely detectable.A decrease in the levels of GSSG also occurred while levelsof ascorbate rose slightly. Similar results were observed withflower buds from ‘Starking Delicious’ and ‘Jonathan’apple trees. These results suggest that the freezing injury to apple flower-budsis closely related to the collapse of the peroxide-scavengingsystems that are coupled with the pentose phosphate cycle. Theresults also suggest that the dysfunction of these peroxide-scavengingsystems is caused by H2O2, which may be produced during freezingand thawing. (Received March 14, 1992; Accepted June 5, 1992)  相似文献   

4.
Populations of Sphaerium corneum (L.) and Pisidium spp. weresampled monthly for 13 months, at 11 sites with a wide rangeof water chemistry in N.W. England. Both genera showed almostyear-round reproduction, but the periods of maximum productionshowed between-population variation. S. corneum adults containedspat at different stages of development and spat size was relatedto number in the brood. Multiple regression analysis with 16water physicochemical variables showed the following to be highlysignificant factors (P<0.01) in the distribution of the molluses(factors in order of importance):- S. corneum: HCO3, K$, Cl, Mg2$, temperature, Ca2$, month; Pisidium spp: PO43–, Mg2$, mud, oxygen, temperature, month. (Received 25 January 1978;  相似文献   

5.
Millhouse, J. and Strother, S. 1987. Further characteristicsof salt-dependent bicarbonate use by the seagrass Zostera muelleri.—J.exp. Bot. 38: 1055–1068. The contribution of HCO3to photosynthetic O2 evolutionin the seagrass Zostera muelleri Irmisch ex Aschers. increasedwith increasing salinity of the bathing seawater when the inorganiccarbon concentration was kept constant. K1/2 (seawater salts)for HCO3 -dependent photosynthesis was 66% of seawatersalinity. Both short- and long-term pretreatment at low salinitiesstimulated photosynthesis in full strength seawater. Twentyfour hours pre-incubation of seagrass plants in 3·0 molm–3 NaHCO3 resulted in increased photosynthesis at allsalinities, apparently due to stimulation of HCO3 use(K1/2 (seawater salts) = 26%). Vmax (HCO3) was not affectedby low salinity pretreatment. The kinetics of HCO3 stimulationby the major seawater cations was investigated. Ca2+ was themost effective cation with the highest Vmax (HCO3) andwith K1/2(Ca2+) = 14 mol m–3. Mg2+ was also very effectiveat less than 50 mol m–3 but higher concentrations wereinhibitory. This inhibition cannot be accounted for solely byprecipitation of MgCO3. Na+ and K+ were both capable of stimulatingHCO3 use. Stimulation was in two distinct parts. Up to500 mol m–3, both citrate and chloride salts gave similarresults (K1/2(Na+) 81 mol m–3, Vmax(HCO3) 0·26µmol O2 mg–1 chl min–1), but use of citratesalts above 500 mol m–2 caused a second stimulation ofHCO3 use (K1/2(Na+) 830 mol m–3, Vmax(HCO3)0·68 µmol O2 mg–1 chl min–1). Vmax(HCO3)for the second-phase Na+ or K+ stimulation was of the same orderas for Ca2+-stimulated HCO3 use. To further characterizesalt-dependent HCO3 use, the sensitivity of photosynthesisto Tris and TES buffers was investigated. The effects of Trisappear to be due to the action of Tris+ causing stimulationof HCO3 -dependent photosynthesis in the absence of salt,but inhibition of HCO3 use in saline media. TES has noeffect on photosynthesis. External carbonic anhydrase, althoughimplicated in salt-dependent HCO3 use in Z. muelleri,could not be detected in whole leaves. Key words: Zostera muelleri, HCO3 use, salinity  相似文献   

6.
Sedimentation behavior of sweet potato glucose 6-phosphate dehydrogenasewas studied using the sucrose density gradient centrifugation.The relative s value to s20, value of alcohol dehydrogenasewas determined to be about 6 in the absence of both NADP$ andglucose 6-phosphate. In the presence of NADP$, the enzyme wassedimented with a relative s value of about 9. The additionof glucose 6-phosphate did not affect the sedimentation behavior.When glucose 6-phosphate was added to the gradient medium containingNDAP$, the enzyme was sedimented with a relative s value ofabout 6 or 7, depending on the concentration of glucose 6-phosphate. 1 Present address: Institute of Applied Microbiology, Universityof Tokyo, Bunkyo-ku. Tokyo, Japan. (Received February 13, 1971; )  相似文献   

7.
The charophyte Lamprothamnium papulosum (Wallr.) J. Gr. is foundat salinities varying from nearly fresh water to twice thatof sea water. It can maintain its turgor constant at 302 mosmolkg–1 (0.73 MPa) when exposed to external osmotic pressuresof 550 to 1350 mosmol kg–1 (1.3–3.3 MPa). Turgorshows a tendency to rise slightly at lower osmotic pressure(388 mosmol kg–1 of turgor at 150 mosmol kg–1 externalosmolality). K+ and Cl are the main solutes in the vacuole,and are most important in controlling internal osmotic pressure.Mg2+, Ca2+, and SO2–4 are present in significant amountsbut their concentrations do not change with changes in externalsalinity. Na+ is present in lower concentration than K+, andplays a minor role in regulating turgor. Sucrose is presentin significant concentrations, but changes little with changesin salinity. Two enzymes involved in sucrose metabolism, sucrosephosphate synthetase (EC 2.4.1.14 [EC] ), and sucrose synthetase (EC2.4.1.13 [EC] ) are active in whole cell extracts of Lamprothamnium.As in the fresh water charophytes, Lamprothamnium membrane potentialmay be depolarized (close to EK) or hyperpolarized, and presumablyof electrogenic origin. Both types of potential are found atall salinities tested.  相似文献   

8.
The activation of ribulose–1, 5-bisphosphate carb-oxylase/oxygenase(Rubisco, EC 4.1.1.39 [EC] ) from the floating angiosperm Spirodelapolyrhiza (L.) Schleid. (giant duckweed) grown at a photon irradianceof 200 or 400 mol photons m–2 s–1 was consistentlylow, in the range of 56–62%. Similarly low values wereobserved with four other emergent aquatic species growing underfull sun irradiance. Transference of Spirodela plants for short(minutes) or long (days) periods to the higher or lower irradianceincreased or decreased, respectively, the activation by onlyabout 15%. Activation was not greatly altered by exposure ofthe plants to full sun irradiance of >2000 mol photons m–2s–1 or CO2 concentrations in air of 0 and 1170 mol mor–1but darkness caused a slow decline to 20% activation. Transientoscillations were observed following a change in irradianceor CO2 concentration indicating that Rubisco was responsiveto environmental perturbations. The low Rubisco activation wasnot due to the tight binding of inhibitors such as carboxyarabinitol-1-phosphate.It is concluded that a substantial proportion of the Rubiscoprotein in these naturally-occurring species may not be usedfor CO2-fixation at any given moment. Key words: Rubisco  相似文献   

9.
SYNOPSIS. Crayfish have a long evolutionary history in temperatefresh water (FW). Ion regulation is challenged by low externalconcentrations of Na, Cl, and Ca (<1 mM). In intermolt theprimary concern is Na and Cl balance; around ecdysis the emphasisswitches to Ca regulation as the cuticle is decalcified/calcified.Compared with marine crustaceans, intermolt crayfish maintaina reduced extracellular (EC) osmolality and have lower permeabilityto both ions and water. Hyperregulation involves active branchialuptake of Na and Cl and the unique ability to produce a hypotonicurine. Ion uptake involves apical electroneutral ion exchange(Na$ for H$; Cl for HCO3–; counterions providedfrom CO2 via carbonic anhydrase) followed by active basolateraltransport of Na via the Na pump, with Cl following passively.Reabsorption of 95% of filtered electrolytes at the antennalgland (kidney) involves similar subcellular mechanisms in amorphologically differentiated region of the distal tubule.Intermolt crayfish exhibit negative Ca balance (passive effluxunopposed by uptake) tolerable in view of the large cuticularCaCO3 reserve. In premolt, cuticular Ca is reabsorbed. A smallamount is stored as gastroliths, the remainder is lost via branchialexcretion and in the discarded exuviae. At ecdysis, FW uptakegenerates the physical force for shedding, leaving the crayfishwith dilute hemolymph and a Ca deficiency. Levels of EC Na andCl are restored by intensive postmolt branchial uptake. Mineralizationof the soft exoskeleton involves remobilization of stored Caand branchial uptake of Ca and HCO3. Transepithelial Ca transportinvolves Ca2$ ATPase and Ca2$/Na$ exchange. The importance ofexternal electrolytes and pH in postmolt ion regulation is explored,as are some allometric considerations.  相似文献   

10.
Using permeabilized characean cells in which the ionic conditionsat the cytoplasmic side of the tonoplast are easily controlled,effects of Ca2+ ion on tonoplast potential were examined. Whenthe cell was treated with 1 µM Ca2+, the tonoplast potential(EM became positive in a complicated manner in Chara corallinawhile it simply became negative in Nitella axilliformis. Whenthe cell was treated with 9-antracenecarboxylic acid, a Cl-channelinhibitor, Em became more negative and the response of Em toCa2+ was significantly suppressed. It is suggested that Ca2+activates Cl-channel at a low concentration and inactivatesat a higher one in C. corallina while it simply inactivate Cl-channelin N. axilliformis. 1Present address: Biological Laboratory, The University of theAir, Wakaba 2-11, Wakaba, 260 Japan. (Received August 22, 1988; Accepted December 26, 1988)  相似文献   

11.
The activity of shikimate: NADP oxidoreductase [EC 1. 1. 1.25] in sweet potato root tissue increased soon after slicing.Enzyme preparations obtained from both sliced tissue and fromfresh tissue probably contained a single enzyme component, andthey showed identical chromatographical behaviour. Km values of the enzyme for NADP and shikimate were 1.0x10–4Mand 1.3 x 10–3M, respectively. Enzyme activity was potentlyinhibited by SH-inhibitors such as p-chloromercuribenzoate andoxidized glutathione. Enzyme activity was affected neither by mononucleotides suchas ATP, ADP and AMP, divalent cations, Mg++, Ca++ and Mn++,nor by metabolites such as tryptophan, phenylalanine, tyrosineand t-cinnamic acid which are involved in aromatic compoundsyntheses. The enzyme rapidly lost its activity. This inactivation reactionshowed a time course consisting of two steps of the first-orderreaction. The inactivated enzyme preparation was not reactivatedby thiol compounds such as cysteine, 2-mercaptoethanol and glutathione,although these reagents, to a certain extent, protected theenzyme from inactivation. The results suggest that denaturationof the enzyme protein was involved in inactivation of the enzyme. 1Part 74 of the phytopathological chemistry of sweet potatowith black rot and injury. 2Present address: Department of Biology, Faculty of Science,Tokyo Metropolitan University, Setagaya-ku, Tokyo. (Received August 5, 1968; )  相似文献   

12.
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   

13.
Mannitol-1-phosphate dehydrogenase (EC 1.1.1.17 [EC] ) and mannitol-1-phosphatase(EC number yet unassigned) were detected in the brown algae,Spatoglossum pacificum and Dictyota dichotoma. The enzymes wereextracted from algal fronds and their properties were investigatedusing partially purified preparations. Mannitol-1-phosphatase shows maximum activity at pH 7. The enzymehad a narrow substrate specificity. The Km value for mannitol-1-phosphateis 8.3x10–4 M (30°C, pH 7.0). The enzyme is activatedby Mg++ and Mn++and is strongly inhibited by PCMB, Hg++and NaF. Mannitol-1-phosphate dehydrogenase showed maximum activitiesat pH values 6.5 and 10.2 in reductive and oxidative reactions,respectively. The dehydrogenase also showed narrow substratespecificity; mannitol-1-phosphate and NAD or fructose-6-phosphateand NADH2 are utilized, respectively, in oxidative and reductivereactions by the enzyme. Km values for these substrates andthe coenzymes are 2.5x10–4 M and 7.1x10–5 M forthe first pair and 2.8x10–4 M and 1.3x10–5 M forthe latter pair. This enzyme was strongly inhibited by PCMBand Hg++, but was only slightly affected by adenosine phosphates. Possible roles of these enzymes in the biosynthesis of mannitolin brown algae are discussed. 1 Contributions from the Shimoda Marine Biological Station ofTokyo Kyoiku University, No. 233. This work was supported inpart by a Grant-in-Aid for Co-operative Research from the Ministryof Education, Japan and in part by a grant to one of us (T.Ikawa) from the Matsunaga Science Foundation. 2 Present address: Chemical and Physical Laboratory, HoechstJapan Research Laboratory, Minamidai, Kawagoe, Japan. (Received February 22, 1972; )  相似文献   

14.
Intact chloroplasts (about 70% Class I chloroplasts) isolatedfrom spinach leaves incorporated 150 nmoles of [1-14C] acetateinto fatty acids per mg chlorophyll in 1 hr at pH 8.3, 25°Cand 25,000 lux. On electron and phase-contrast microscopiescombined with hypotonic treatment of chloroplasts, this syntheticactivity was shown to be proportional to the percentage of ClassI chloroplasts in the preparation. Light was necessary for thesynthesis, the activity in the complete reaction mixture inthe dark being only 2% of that in the light. The synthetic activityincreased with increasing intensities of light to reach saturationat 6,000 lux. CoA and ATP were most effective as cofactors,HCO3, HPO42–, Mg2$ and Mn2$ were less effective.ATP could be replaced by ADP in the presence of Pi, suggestingpossible supply of ATP by photophosphorylation. Omission ofthe NADPH-generation system and NADH did not affect the synthesis,indicating sufficient provision of endogenous NADPH and NADHin intact chloroplasts under light. Addition of DTE did notcause recovery of the synthetic activity of intact chloroplastsin the dark. 1 Present address: Radioisotope Centre, University of Tokyo,Yayoi, Bunkyo, Tokyo 113, Japan. (Received August 26, 1974; )  相似文献   

15.
Low concentrations of ammonia and methylamine greatly increaseCl influx into Chara corallina. Both amines have theirmaximum effect at pH 6.5–7.5. The amine stimulation ofCl influx is small below about pH 5.5. Above pH 8.5 theremay be inhibition of influx by amines. Concentrations of 10–25µM ammonia are sufficient to cause the maximum stimulationof Cl influx; the corresponding methylamine concentrationsare 0.1–0.2 mM. It is concluded that entry of amine cations(NH4$ and CH3NH3$), rather than unionized bases (NH3 and CH3NH2),causes Cl transport to be increased. Increases in rates of Cl transport are not necessarilyaccompanied by effects on HCO3$ assimilation and OH efflux.Measurements of localized pH differences at the cell surfaceand of circulating electric currents in the bathing solutionshow that these phenomena are only significantly affected byammonia at or above 50 µM and by methylamine at or above1.0 mM. The significance of the effects of amines is assessedin relation to current ideas about transport of Cl, HCO3,and OH.  相似文献   

16.
At concentrations of CO2 less than saturating, carbonic anhydrase(EC 4.2.1.1 [EC] ) stimulates the carboxylation of ribulose bisphosphatecatalysed by ribulose bisphosphale carboxylase (EC 4.1.1.3 [EC] .9)in vitro. This is not through any beneficial association ofthe two enzymes but is a consequence of the increased rate ofconversion of HCO3 ion to CO2, the substrate for thecarboxylation. Carbonic anhydrase should always be includedin reaction mixtures used to determine the Michaelis constantof ribulose bisphosphate carboxylase for CO2 where fixationof radioactive CO2 into phosphoglycerate is the basis of rateestimation. The effect is to decrease the value obtained forthe Michaelis constant.  相似文献   

17.
When Chlorella vulgaris 11h, Chlorella vulgaris C-l, Chlamydomonasreinhardtii, Chlamydomonas moewusii, Scenedesmus obliquus, orDunaliella tertiolecta were illuminated in with 0.5 mM NaHCO3,the pH of the medium increased in a few minutes from 6 to about9 or 10. The alkalization, which was accompanied by O2 evolution,was dependent on light, external dissolved inorganic carbon(DIC) as HCO-3, and algae grown or adapted to a low, air-levelCO2 in order to develop a DIC concentrating mechanism. Therewas little pH increase by algae without a DIC concentratingprocess from growth on 3% CO2 in air. Photosynthetic O2 evolutionwithout alkalization occurred using either internal DIC or externalCO2 at acidic pH. The PH increase stopped between pH 9 to 10,but the alkalization would restart upon re-acidification betweenpH 6 and 8. Alkalization was suppressed by the carbonic anhydraseinhibitors, acetazolamide, ethoxyzolamide or carbon oxysulfide.The pH increase appeared to be the consequence of the externalconversion of HCO3 into CO2 plus OH during photosynthesisby cells with a high affinity for CO2 uptake. Cells grown onhigh CO2 to suppress the DIC pump, when given low levels ofHCO3 in the light, acidified the medium from pH 10 to7. Air adapted Scenedesmus cells with a HCO3 pump, aswell as a CO2 pump, alkalized the medium very rapidly in thelight to a pH of over 10, as well as slower in the dark or inthe light with DCMU or without external DIC and O2 evolution.Alkalization of the medium during photosynthetic DIC uptakeby algae has been considered to be part of the global carboncycle for converting H2CO3 to HCO3 and for the formationof carbonate salts by calcareous algae from the alkaline conversionof bicarbonate to carbonate. These processes seem to be a consequenceof the algal CO2 concentrating process. 1Present address: Department of Biology, Faculty of Science,Niigata University, Niigata, 950-21 Japan.  相似文献   

18.
High activity of phosphoenolpyruvate (PEP)-carboxykinase, orADP: oxalacetate (OAA) carboxy-lyase activity (a kind of EC4. 1. 1. 32) was discovered in enzyme extracts or partiallypurified preparations obtained from the brown algae, Eiseniabicyclis, Dictyota dichotoma, Spatoglossum pacificum; and Hizikiafusiformis. Enzyme activities were determined by measuring theradioactivity incorporated in the products of dark 14CO2-fixationand by spectrophotometric determinations. Except for the lowactivity of "malic enzyme" (EC 1. 1. 1.40), no activities ofother carboxylases, i.e. PEP-carboxylase, PEP-carboxytransphosphorylase,and pyruvate carboxylase could be detected in algal extractsprepared under various conditions. Malate dehydrogenase (EC1. 1. 1. 37), fumarase (EC 4. 2. 1. 2), and glutamic: oxalacetictransaminase (EC 2. 6. 1. 1) were also detected. The algal PEP-carboxykinase required ADP and Mn2+ for maximumactivity in the carboxylation reaction; and ATP and Mn2+, butnot GTP, for maximum activity in both the decarboxylation andOAA-14CO2-exchange reactions. The optimum pH of purified PEP-carboxykinase was in the regionof 7.0 to 7.3 in both the carboxylation and decarboxylationreactions, and its Km values for HCO3, PEP, and ADP were10 mM, 0.3 mM, and 0.07 mM, respectively, in the carboxylationreaction, and values for OAA and ATP were 0.05 mM and 0.4 mM,respectively, in the decarboxylation reaction. Furthermore,the decarboxylation reaction was markedly inhibited by 20 mMHCO3. The physiological role of PEP-carboxykinase as the enzyme responsiblefor the entrance reaction of the dark CO2-fixation is discussed. 1 Contributions from the Shimoda Marine Biological Station ofTokyo Kyoiku University, No. 236. This work was supported inpart by a Grant-in-Aid for Co-operative Research from the Ministryof Education, Japan and Matsunaga Science Foundation (to T.Ikawa). 2 Present address: Department of Antibiotics, the National Instituteof Health, Shinagawa, Tokyo, Japan. (Received February 22, 1972; )  相似文献   

19.
A procedure is described for the purification of phosphoenolpyruvatecarboxylase (EC 4.1.1.31 [EC] ) and NADP-dependent malic enzyme (EC1.1.1.40 [EC] ) from sugar cane leaves. Each enzyme was purified tohomogeneity as judged by sodium dodecyl sulfate-polyacrylamidegel electro-phoresis, with about 30% yield. Phosphoenolpyruvatecarboxylase was purified 54-fold. A molecular weight of 400,000and a homotetrameric structure were determined for the nativeenzyme. The purified carboxylase had a specific activity of20.0 {diaeresis}mol (mg protein)–1 min–1, and wasactivated by glucose-6-phosphate and inhibited by L-malate.Km values at pH 8.0 for phosphoenolpyruvate and bicarbonatewere 0.25 and O.l0 mM, respectively. NADP-malic enzyme, 356-foldpurified, exhibited a specific activity of 71.2 {diaeresis}mol(mg protein)–1 min–1 and was characterized as ahomotetramer with native molecular weight of 250,000. Purifiedmalic enzyme showed an absolute specificity for NADP+ and requireda divalent metal ion for activity. Km values of 0.33 and 0.008mM for L-malate and NADP+, respectively, were determined. Thisenzyme was inhibited by several organic acids, including ketoand amino acids; while succinate and citrate increased the enzymeactivity when assayed with 10{diaeresis}M L-malate. The effectsshown by amino acids and by citrate were dependent on pH, beinghigher at pH 8.0 than at pH 7.0. (Received October 26, 1988; Accepted February 3, 1989)  相似文献   

20.
Hydrodictyon africanum can photosynthesize at high pH underconditions in which HCO3 rather than CO2 is the carbonspecies entering the cell. A passive entry of HCO3 seemsunlikely; a metabolic HCO3 pump is proposed. It is possiblethat such a pump is related to a light-dependent reaction specificto the use of HCO3. This reaction is dependent on photosystem2, but appears to be independent of ATP. These characteristicsare similar to those of active lightdependent Cl influx in H.africanum, and suggest a similar energy source for the two pumps.The HCO3 pump may be electrogenic.  相似文献   

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