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1.
Abstract: Antibody Ab262 was raised against a synthetic τ peptide (SKIGSTENLK, amino acids 258–267 of τ, termed Ser262 peptide). The antibody was more reactive with Ser262 peptide and unphosphorylated τ than a related phosphopeptide [SKIGS(P)TENLK, termed P-Ser262 peptide] and τ phosphorylated by a partially purified kinase, glycogen synthase kinase (GSK) 3β. Ab262 reacted poorly with a peptide having the sequence DRVQSKIGSLD (amino acids 348–358). Treatment of P-Ser262 peptide or GSK 3β phosphorylated τ with alkaline phosphatase increased Ab262 immunoreactivity, indicating that Ab262 is a reagent useful for studying τ phosphorylation at the Ser262 residue. The Ab262 immunoreactivity was detected in τ from normal brains and Alzheimer paired helical filament (PHF-τ) and in PHFs. Alkaline phosphatase treatment had no effect on the Ab262 immunoreactivity of normal τ and PHF-τ but altered the Tau-1 and PHF-1 immunoreactivities. τ proteins from rat brains at 3 and 8 h postmortem exhibited 5 and 19%, respectively, more Ab262 immunoreactivity than τ from fresh tissues. In comparison, rat τ at 8 h postmortem was 40% more immunoreactive with Tau-1. The results suggest that Ser262 is not a major phosphorylation site in vivo. Moreover, there is little or no difference between PHF-τ and normal τ in the extent of phosphorylation at Ser262 . 相似文献
2.
The binding of plasmin to Streptococcus uberis strain 0140 J was optimal in the pH range 5·0–5·5. Plasmin binding decreased exponentially with increasing NaCl concentration (0–0·8 mol l−1 ), reaching a minimum at NaCl concentrations exceeding 0·55 mol l−1 . Neither K+ , Mg2+ nor the metal chelator EDTA had any effect on the interaction. Plasmin binding was prevented, in a concentration-dependent manner, by the amino acids lysine, arginine and ε-aminocaproic acid. Bound plasmin was also eluted from the bacterial cell using the same amino acids. Bound plasmin was lost from the bacterium in a time- and temperature-dependent fashion, the rate of plasmin loss increased with increasing temperature over the range 4–55 °C, and the elution of plasmin from live and heat-killed bacteria was similar. Cell-bound plasmin was only partially inhibited by the physiological inhibitor α2 -antiplasmin whereas the serine protease inhibitor aprotinin, and the active site titrant p -nitrophenyl- p -guanidiniobenzoate, inhibited the activity of the cell-bound plasmin by more than 95%. 相似文献
3.
Purification and characterization of the major β-1,4-endoglucanase from Thermomonospora curvata 总被引:1,自引:1,他引:0
The major β-1,4-endoglucanase (EG) of the thermophilic actinomycete, Thermomonospora curvata , contributed over 80% of the total EG activity recovered from cell-free culture fluid after growth on cellulose. The enzyme was purified to electrophoretic homogeneity by ammonium sulphate precipitation, ion-exchange chromatography and size exclusion HPLC. This monomeric enzyme had a specific activity of 750 IU mg−1 when assayed with 2.5% (w/v) carboxymethyl cellulose (CMC) at 70°C, pH 6.0. Highest activity was observed on CMC with a degree of polymerization of 3200. The EG was stable for 48 h at 60°C, pH 6.0 and had a half-life of 30 min at 80°C; temperature and pH optima were 70–73°C and 6.0–6.5, respectively. The mol. wt was 100000 and the pI was 4.0. The K m and V max values were 7.33 mg ml−1 and 833 μmol min−1 , respectively. EG activity was inhibited by Fe2 + , Hg2 + , Ag+ and Pb2 + , and enhanced by dithiothreitol and Zn2 + . The first 12 amino acid residues at the N -terminus were: Asp-Glu-Val-Asp-Glu-Ile-Arg-Asn-Gly-Asp-Phe-Ser. Glutamic and aspartic acid constituted 24% of the total amino acid composition; no amino sugar was found. 相似文献
4.
Abstract: The terminal phosphate group of ATP was transferred to ADP by an enzyme present in the soluble core proteins of adrenal medulla catecholamine storage vesicles. It was purified 10–30-fold by DEAE Sephadex chromatography (Fraction I). The enzyme required divalent metal ions for activation; Mn2+ was almost as effective as Mg2+ , but Ca2+ was only a weak activator. Activation by Mg2+ took place over a very narrow concentration range (0.5–3 m m ). The specificity of the enzyme activity to nucleoside triphosphates was broad, to the nucleoside diphosphates narrow, favouring adenosine diphosphate. In dependence on the pH the activity increased from pH 4 to pH 7 and remained constantly high between pH 7 and 9. The Arrhenius plot was linear between 5 and 70°C, with an activation energy of 11.1 kcal/mol. The phosphoryl group transfer reaction depended on the function of thiol groups; p -hydroxymercuribenzoate inhibited 50% of the enzyme activity; dithioerythritol reactivated it completely. Gel electrophoresis revealed that in Fraction I, a protein of molecular weight about 45,000, was enriched compared with the total soluble proteins. The enzyme-enriched Fraction I differed significantly in its relative amino acid composition from that of the total soluble proteins; in general, the acidic amino acids were reduced and the more basic acids enhanced. 相似文献
5.
Gregory A. Jicha Audrey O' Donnell† Charles Weaver‡ Ruth Angeletti† & Peter Davies‡ 《Journal of neurochemistry》1999,72(1):214-224
Abstract : Immunoaffinity-purified paired helical filaments (PHFs) from Alzheimer's disease (AD) brain homogenates contain an associated protein kinase activity that is able to induce the phosphorylation of PHF proteins on addition of exogenous MgCl2 and ATP. PHF kinase activity is shown to be present in immunoaffinity-purified PHFs from both sporadic and familial AD, Down's syndrome, and Pick's disease but not from normal brain homogenates. Although initial studies failed to show that the kinase was able to induce the phosphorylation of tau, additional studies presented in this article show that only cyclic AMP-dependent protein kinase-pretreated recombinant tau is a substrate for the PHF kinase activity. Deletional mutagenesis, phosphopeptide mapping, and site-directed mutagenesis have identified the PHF kinase phosphorylation sites as amino acids Thr361 and Ser412 in htau40. In addition, the cyclic AMP-dependent protein kinase phosphorylation sites that direct the PHF kinase have been mapped to amino acids Ser356 and Ser409 in htau40. Additional data demonstrate that these hierarchical phosphorylations in the extreme C terminus of tau allow for the incorporation of recombinant tau into exogenously added AD-derived PHFs, providing evidence that certain unique phosphorylations of tau may play a role in the pathogenesis of neurofibrillary pathology in AD. 相似文献
6.
Natranaerobius thermophilus is an unusual extremophile because it is halophilic, alkaliphilic and thermophilic, growing optimally at 3.5 M Na+ , pH55°C 9.5 and 53°C. Mechanisms enabling this tripartite lifestyle are essential for understanding how microorganisms grow under inhospitable conditions, but remain unknown, particularly in extremophiles growing under multiple extremes. We report on the response of N. thermophilus to external pH at high salt and elevated temperature and identify mechanisms responsible for this adaptation. N. thermophilus exhibited cytoplasm acidification, maintaining an unanticipated transmembrane pH gradient of 1 unit over the entire extracellular pH range for growth. N. thermophilus uses two distinct mechanisms for cytoplasm acidification. At extracellular pH values at and below the optimum, N. thermophilus utilizes at least eight electrogenic Na+ (K+ )/H+ antiporters for cytoplasm acidification. Characterization of these antiporters in antiporter-deficient Escherichia coli KNabc showed overlapping pH profiles (pH 7.8–10.0) and Na+ concentrations for activity ( K 0.5 values 1.0–4.4 mM), properties that correlate with intracellular conditions of N. thermophilus . As the extracellular pH increases beyond the optimum, electrogenic antiport activity ceases, and cytoplasm acidification is achieved by energy-independent physiochemical effects (cytoplasmic buffering) potentially mediated by an acidic proteome. The combination of these strategies allows N. thermophilus to grow over a range of extracellular pH and Na+ concentrations and protect biomolecules under multiple extreme conditions. 相似文献
7.
Uptake of amino acids and peptides by developing barley embryos 总被引:1,自引:0,他引:1
Developing embryos of barley ( Hordeum vulgare L. cv. Bomi) detached 21–27 days after anthesis took up 1 mM [14 C]-glutamine at pH 5 and 30°C at a rate of about 20 nmol embryo−l h−1 (5 μol g−1 h−1 ). The uptake was inhibited by about 50% by di-nitrophenol and by about 80% by 300 m M unlabelled glutamine or alanine. The bulk of the uptake appeared, therefore, to be due to carrier-mediated active transport. The pH optimum of the uptake was 4.5. Leucine, proline, lysine, arginine and as-paragine were taken up at approximately similar rates as glutamine, and they also inhibited the uptake of glutamine. This, suggests that the uptake of glutamine was at least partly due to an unspecific carrier(s) also shared by other amino acids. The embryos also took up the dipepti.de glycykarcosine; the rate was about 6 nmol embryo−1 h−1 (1.5 μol g−1 h−1 ) (2 mM glycylsarcosine, pH 4.5, 30°C). The uptake was inhibited by about 70% by dinitrophenol or by 300 m M glycylglycine. This indicates that the bulk of the uptake was due to carrier-mediated active transport. The pH optimum of the uptake was about 4.5.
The rates of glutamine and glycylsarcosine uptake increased during the early and middle stages of embryo development (until day 28 after anthesis), but decreased towards the end of the maturation of the grain. These changes, as well as the relatively high activities, suggest that carrier-mediated active uptake of amino acids, and possibly also that of peptides, plays a role in the nutrition of the developing embryo. 相似文献
The rates of glutamine and glycylsarcosine uptake increased during the early and middle stages of embryo development (until day 28 after anthesis), but decreased towards the end of the maturation of the grain. These changes, as well as the relatively high activities, suggest that carrier-mediated active uptake of amino acids, and possibly also that of peptides, plays a role in the nutrition of the developing embryo. 相似文献
8.
The possibility to induce nitrate reductase (NR; EC 1.6.6.2) in needles of Scots pine ( Pinus sylvestris L.) seedlings was studied. The NR activity was measured by an in vivo assay. Although increased NR activities were found in the roots after application of NO3 − , no such increase could be detected in the needles. Detached seedlings placed in NO3 − solution showed increasing NR activities with increasing NO3 − concentrations. Exposure of seedlings to NOx (70–80 ppb NO2 and 8–12ppb NO) resulted in an increase of the NR activity from 10–20 nmol NO2 − (g fresh weight)−1 h−1 to about 400 nmol NO2 − (g fresh weight)−1 h−1 . This level was reached after 2–4 days of exposure, thereafter the NR activity decreased to about 200 nmol NO2 − (g fresh weight)−1 h−1 . Analyses of free amino acids showed low concentrations of arginine and glutamine in NOx -fumigated seedlings compared to corresponding controls. 相似文献
9.
Miriam Banay-Schwartz D. N. Teller Babette Horn A. Lajtha 《Journal of neurochemistry》1977,29(3):403-410
Abstract— Mouse brain slices were depleted of K+ by three 10-min incubations-in oxygenated HEPES-buffered medium lacking glucose and K+ . Addition of K+ or Rb+ (or Cs+ , to a smaller degree) with glucose, or with succinate, malate, and pyruvate (SMP) before incubation at 37°C with 14 C-amino acids restored active low-affinity transport of d -Glu, α-aminoisobutyrate (AIB), GABA, Gly, His, Val, Leu, Lys, and Orn. Ouabain at 1–2μ m with Rb+ was more inhibitory with SMP than with glucose, suggesting that the glycoside may affect specific energy coupling to transport. Valinomycin, in contrast, showed no specificity of inhibition of amino acid uptake with glucose or SMP and K+ or Rb+ . Cs+ partially restored amino acid uptake, but Li+ was less effective than Cs + . NaF at 10 m m with SMP + Rb+ , or SMP + K+ did not inhibit amino acid uptake. Therefore, it was possible to dissociate glycolysis and Na+ , K + -ATPase activity from amino acid transport. The ion replacements for K + that supported active amino acid transport indicate that the specificity of ions in possible ionic gradients for transport energetics should be reexamined. 相似文献
10.
Minimum inhibitory concentrations (MIC) of undissociated lactic, acetic and formic acids were evaluated for 23 strains of enterobacteria and two of Listeria monocytogenes. The evaluation was performed aerobically and anaerobically in a liquid test system at pH intervals of between 4.2 and 5.4. Growth of the enterobacteria was inhibited at 2–11 mmol 1−1 , 0.5–14 mmol 1−1 and 0.1–1.5 mmol 1−1 of undissociated lactic, acetic and formic acids, respectively. The MIC value was slightly lower with anaerobic conditions compared with aerobic conditions. The influence of protons on the inhibition was observed for acetic acid at the low pH values. Undissociated lactic acid was 2 to 5 times more efficient in inhibiting L. monocytogenes than enterobacteria. Acetic acid had a similar inhibitory action on L. monocytogenes compared with enterobacteria. Inorganic acid (HCl) inhibited most enterobacteria at pH 4.0; some strains, however, were able to initiate growth to pH 3.8. The results indicate that the values of undissociated acid which occur in a silage of pH 4.1–4.5 are about 10–100 times higher than required in order to protect the forage from the growth of enterobacteria and L. monocytogenes. 相似文献
11.
Abstract: Recent evidence suggests that β-amyloid peptide (β-AP) may induce tau protein phosphorylation, resulting in loss of microtubule binding capacity and formation of paired helical filaments. The mechanism by which β-AP increases tau phosphorylation, however, is unclear. Using a hybrid septal cell line, SN56, we demonstrate that aggregated β-AP1–40 treatment caused cell injury. Accompanying the cell injury, the levels of phosphorylated tau as well as total tau were enhanced as detected immunochemically by AT8, PHF-1, Tau-1, and Tau-5 antibodies. Alkaline phosphatase treatment abolished AT8 and PHF-1 immunoreactivity, confirming that the tau phosphorylation sites were at least at Ser199/202 and Ser396 . In association with the increase in tau phosphorylation, the immunoreactivity of cell-associated and secreted β-amyloid precursor protein (β-APP) was markedly elevated. Application of antisense oligonucleotide to β-APP reduced expression of β-APP and immunoreactivity of phosphorylated tau. Control peptide β-AP1–28 did not produce significant effects on tau phosphorylation, although it slightly increased cell-associated β-APP. These results suggest that βAP1–40 -induced tau phosphorylation may be associated with increased β-APP expression in degenerated neurons. 相似文献
12.
A GC-MS method for determination of amino acid uptake by plants 总被引:5,自引:0,他引:5
In this study, we present a rapid, robust and sensitive method for quantification of plant amino acid uptake using universally (U) (13 C, 15 N)-labelled amino acids and gas chromatography-mass spectrometry (GC-MS). Amino acids were analysed as their tert -butyldimethylsilyl (tBDMS) derivatives and displayed detection limits in the range 10–100 fmol on column, depending on the amino acid. The technique allows for simultaneous detection and quantification of both unlabelled and isotopically labelled species of amino acids. This makes simple quantification of plant amino acid uptake from an isotopically labelled source possible. The analytical variation was low, concerning total amino acid concentrations (relative standard deviation, rsd , less than 5.3%) as well as enrichment of U-13 C, 15 N-labelled glycine (Gly), arginine (Arg) and glutamic acid (Glu) ( rsd <2.1%). An application of the GC-MS method was conducted on non-mycorrhizal Pinus sylvestris roots supplied with U-13 C, 15 N-labelled amino acids. Intact, labelled amino acids were traced in root extracts. This provided conclusive evidence of plant root uptake of intact amino acids. Uptake rates of the three amino acids Gly, Glu and Arg in the range 0.5–37.9 μmol g−1 dry weight h−1 were recorded. These rates are comparable with those recorded in earlier studies of amino acid uptake, using other methods, as well as uptake rates measured for nitrate and ammonium. 相似文献
13.
Abstract— Angiotensin converting enzyme (peptidyl dipeptide hydrolase EC 3.4.15.1) was extracted from particulates of rat brain using the nonionic detergent Triton X-100. Enzyme activity in subcellular fractions was associated with purified synaptosomes and present in the microsomal fraction, but absent in purified mitochondria and water-shocked myelin. Partial purification was achieved by chromatography on DEAE-cellulose and hydroxylapatite columns. The enzyme had a pH optimum of pH 7–8 and an apparent Km of 2.2 m m using hippuryl-histidyl-leucine as substrate; it was chloride dependent, inhibited by (Sar1 -Ala8 )-angiotensin-II (saralasin), and, at lower concentrations, by the specific nonapeptide inhibitor SQ 20881. Associated with the purified enzyme was an aminopeptidase, cleaving N-terminal Asp from the native substrate, which could be involved in the production of the active heptapeptide, angiotensin III (des-Asp-angiotensin-II). Also present was a carboxypeptidase-like enzyme removing C-terminal Phe following the liberation of His-Leu by converting enzyme, which may be involved in the inactivation of angiotensin II or III. 相似文献
14.
Immobilization of dissolved organic matter from groundwater discharging through the stream bed 总被引:5,自引:0,他引:5
SUMMARY. 1. In laboratory experiments, 9.7–25.7% of dissolved organic carbon (DOC) in groundwater (at concentrations of 18.7–24.8 mg 1-−1 ) was immobilized after perfusion through 8-cm-deep (22-cm-diameter) cores of stony stream-bed substratum.
2. This represented immobilization rates of 7.1–23.5 mg m−2 h−1 or, extrapolated across the year, potential immobilization rates within the stream bed of 62.2–205.9g m−2 yr−1 . Actual rates in the entire stream bed were probably higher because perfusion through the experimental cores did not reduce groundwater DOC concentrations to levels measured in the adjacent stream.
3. Natural concentrations of dissolved free amino acids (DFAAs) in groundwater were generally unchanged following perfusion through the cores, suggesting the maintenance of a dynamic equilibrium in their concentrations.
4. Selective enrichments of amino acids in groundwater (up to 20-fold) were entirely immobilized following perfusion, indicating their rapid retention and flux in this environment. Thus, immobilization of the bulk DOC in stream-bed cores probably did not reflect net reductions in dissolved free, low-molecular-weight material, with higher molecular weight, more 'refractory' material being immobilized instead.
5. We conclude that groundwater can contribute substantial amounts of DOC, both high and low molecular weight, to a stream ecosystem. The stream bed is the site at which much of this material could be initially immobilized and made available to the stream trophic structure. 相似文献
2. This represented immobilization rates of 7.1–23.5 mg m
3. Natural concentrations of dissolved free amino acids (DFAAs) in groundwater were generally unchanged following perfusion through the cores, suggesting the maintenance of a dynamic equilibrium in their concentrations.
4. Selective enrichments of amino acids in groundwater (up to 20-fold) were entirely immobilized following perfusion, indicating their rapid retention and flux in this environment. Thus, immobilization of the bulk DOC in stream-bed cores probably did not reflect net reductions in dissolved free, low-molecular-weight material, with higher molecular weight, more 'refractory' material being immobilized instead.
5. We conclude that groundwater can contribute substantial amounts of DOC, both high and low molecular weight, to a stream ecosystem. The stream bed is the site at which much of this material could be initially immobilized and made available to the stream trophic structure. 相似文献
15.
Abstract: A diphtheria toxin-neurotrophin-4/5 (NT-4/5) chimera (DAB389 -NT4), in which the native receptor binding domain of diphtheria toxin was replaced with a synthetic gene encoding rat NT-4/5, was expressed, refolded, and purified. This fusion toxin has a deduced molecular mass of 60,163 and is formed by joining the first 389 amino acids of diphtheria toxin to amino acids 1–130 of mature rat NT-4/5, using an NH2 -terminal bridge of 33 additional amino acids including six consecutive histidines. Neural cell types expressing only p75LNGFR or p75LNGFR and full-length or truncated TrkB were used to evaluate the cytotoxic efficacy of DAB389 -NT4. The fusion toxin produced a concentration-dependent killing of all cell populations, with LC50 values that largely reflected the known NT-4/5 binding affinities for these receptor proteins. Mean LC50 values ranged from 2,960 p M in p75LNGFR -expressing neuro-2a neuroblastoma cells to 1,075 and 70 p M , respectively, in hippocampal astrocytes (p75LNGFR+ /truncated TrkB+ ) and cerebellar granule cells (p75LNGFR+ /TrkB+ ). The LC50 for DAB389 -NT4 in receptor-negative 3T3 fibroblasts was 20 n M . NT-4/5 and brain-derived neurotrophic factor but not ciliary neurotrophic factor added in excess neutralized DAB389 -NT4 cytotoxicity. NT-4/5, however, did not reduce the cytotoxicity of intact diphtheria toxin. 相似文献
16.
Adsorption of Suwannee River fulvic acid (SRFA) to algal surfaces of three green algae was studied at environmentally relevant pH values (4 –7) and SRFA concentrations (5–100 mg·L − 1 ). The influence of adsorbed SRFA on carbon uptake of Scenedesmus subspicatus Chodat was also examined. Although no adsorption was observed at neutral pH values (pH 6 and 7), at pH 4 up to 31 mg SRFA·m − 2 and at pH 5 up to 4 mg SRFA·m − 2 was adsorbed to the algal surfaces. Electrophoretic mobility measurements of S. subspicatus demonstrated an increase in the negative surface charge of the alga in the presence of SRFA at pH 4. The adsorbed SRFA also influenced 14 C uptake in S. subspicatus; in this case, enhanced carbon uptake could be related to the amount of adsorbed SRFA. The binding of humic substances by algal surfaces was interpreted as the result of hydrogen bonding and hydrophobic interactions. 相似文献
17.
18.
Spirochaeta smaragdinae sp. nov., a new mesophilic strictly anaerobic spirochete from an oil field 总被引:1,自引:0,他引:1
Michel Magot Marie-Laure Fardeau Odile Arnauld Colette Lanau Bernard Ollivier P. Thomas B.K.C. Patel 《FEMS microbiology letters》1997,155(2):185-191
An obligately anaerobic spirochete designated strain SEBR 4228T (T = type strain) was isolated from an oil field of Congo, Central Africa. The strain grew optimally with a sodium chloride concentration of 5% (sodium chloride concentration growth range 1.0–10%) at 37°C (growth temperature range 20–40°C) and pH of 7.0–7.2 (pH growth range pH 5.5–8.0). Strain SEBR 4228T grew on carbohydrates (glucose, fructose, ribose, d -xylose, galactose, mannitol and mannose), glycerol, fumarate, peptides and yeast extract. Yeast extract was required for growth and could not be replaced by vitamins. It reduced thiosulfate and sulfur, to H2 S. Glucose was oxidised to lactate, acetate, CO2 and H2 S in the presence of thiosulfate but in its absence lactate, ethanol, CO2 and H2 were produced. Fumarate was fermented to acetate and succinate. The G+C content of strain SEBR 4228T was 50%. Strain SEBR 4228T was spiral shaped measuring 5–30 by 0.3–0.5 μm and was motile with a corkscrew-like motion. Electron microscopy revealed the presence of periplasmic flagella in a 1-2-1 arrangement. Strain SEBR 4228T possessed features typical of the members of the genus Spirochaeta . 16S rRNA sequence analysis revealed that it was closely related to Spirochaeta bajacaliforniensis (similarity 98.6%). The lack of DNA homology with S. bajacaliforniensis (38%), together with other phenotypic differences, indicated that strain SEBR 4228T is a new species, which we have designated Spirochaeta smaragdinae . The type strain is SEBR 4228T (= DSM 11293). 相似文献
19.
Abstract An Fe(II)-oxidizing enzyme was purified from Thiobacillus ferrooxidans to an electrophoretically homogeneous state. The enzyme showed absorption peaks at 282 and 382 nm and contained 18–20 atoms of non-haem iron and 6 atoms of inorganic sulphide in the molecule. Its molecular weight was determined to be 63 000 by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulphate. The enzyme rapidly reduced T. ferrooxidans ferricytochrome c -552 with Fe2+ ions at pH 3.5. Rusticyanin was not reduced by the enzyme with Fe2+ ions, while it was reduced rapidly by the enzyme with the ions in the presence of a small amount of cytochrome c -552. 相似文献
20.
The acquisition and accumulation of inorganic carbon by the unicellular green alga Chlorella ellipsoidea 总被引:3,自引:0,他引:3
Abstract. The uptake and accumulation of inorganic carbon has been investigated in Chlorella ellipsoidea cells grown at acid or alkaline pH. Carbonic anhydrase (CA) was detected in ceil extracts but not in intact cells and CA activity in acid-grown cells was considerably less than that in alkali-grown cells. Both cell types demonstrates low K1/2 (CO2 ) values in the range pH 7.0–8.0 and these were unaffected by O2 concentration. The CO2 compensation concentrations of acid- and alkali-grown cells suspended in aqueous media were not significantly different in the range of pH 6.0–8.0, but at pH 5.0, the CO2 compensation concentrations of acid-grown cells (57.4cm3 m−3 ) were lower than those of alkali-grown cells (79.2cm3 m−3 ). The rate of photo-synthetic O2 evolution in the range pH 7.5–8.0 exceeded the calculated rate of CO2 supply two- to three-fold, in both acid- and alkali-grown cells, indicating that HCO3 − was taken up by the cells. Accumulation of inorganic carbon was measured at pH 7.5 by silicone-oil centri-fugation, and the concentration of unfixed inorganic carbon was found to be 5.1 mol m−3 in acid-grown and 6.4mol m−3 in alkali-grown cells. These concentrations were 4.6- and 5.9-fold greater than in the external medium. These results indicate that photorespiration is suppressed in both acid- and alkali-grown cells by an intracellular accumulation of inorganic carbon due, in part, to an active uptake of bicarbonate. 相似文献