共查询到20条相似文献,搜索用时 35 毫秒
1.
Ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPCO) rapidly extracted from leaves of wheat ( Triticum aestivum) and purified activated RuBPCO were incubated in the presence and absence of 20 millimolar HCO 3− and changes in activation state were followed. Rapid inactivation occurred in the presence, but not in the absence, of HCO 3−. Effects of CO 2 concentration and pH during preincubation before assay on activation state of RuBPCO were investigated in equilibrium studies. Twenty percent inactivation occurred at high CO 2 concentration if pH was high, but not if it was low, suggesting that RuBPCO was inactivated by HCO 3−. The inactivation by HCO 3− was more rapid than the dissociation of activating CO 2 in CO 2-free buffer (both in the presence of 20 millimolar MgCl 2), suggesting that HCO 3− was bound to the active enzyme complex. The dissociation of inactivating HCO 3− from the enzyme was slow enough that inhibition could be demonstrated in experiments with HCO 3− treatments during preincubation and constant conditions during assay. Inorganic phosphate did not seem to interfere with the binding of HCO 3−. 相似文献
2.
Information is given concerning two standard buffer solutions suitable as pH references in 30, 40, and 50 mass% dimethyl sulfoxide (DMSO)/H 2O mixed solvents at subzero temperatures from −20 to 0 °C, with the intention of establishing a pH (designated pH *) scale. The two buffers selected were the ampholytes N,N-bis(2-hydroxyethyl)-2-aminoethane sulfonic acid (“bes”) and N-tris(hydroxymethyl)methylglycine (“tricine”), and the reference standard consisted of equal molal quantities of the buffer and its respective sodium salt. The assignment of pH * values was based on measurements of the emf of cells without liquid junction of the type: Pt;H 2(g,1 atm) ¦Bes, Na Besate, NaCl ¦ AgCl;Ag and Pt;H 2(g,1 atm) ¦Tricine, Na Tricinate, NaCl ¦AgCl;Ag and the pH * was derived from a determination of K2, the equilibrium constant for the dissociation process (Buffer) ±/ai (Buffer) − + H +. 相似文献
3.
The rate of O 2 evolution and alkalization of the medium in low CO 2− grown Anabaena variabilis was observed as affected by the pH in the medium. Both rates are severely inhibited by pH values higher than 9.5, but the latter is more sensitive to this treatment. This finding, as well as the lag observed in alkalization of the medium, but not in O 2 evolution, following the addition of HCO 3− indicates that the transport of HCO 3 and OH − (or H +) are not compulsorily coupled. The inhibition of photosynthesis by strongly alkaline pH is attributed to an alteration of the internal pH and, hence, the rate of carboxylation. This conclusion is supported by data showing that the rate of O 2 evolution is affected by pH more strongly at saturating [HCO 3−] than at limiting [HCO 3−]. Also, the rate of O 2 evolution at saturating light intensity is affected by pH more strongly than is the initial slope of the curve against light intensity or the rate of dark respiration. 相似文献
4.
γ-Aminobutyraldehyde dehydrogenase from Escherichia coli K-12 has been purified and characterized from cell mutants able to grow in putrescine as the sole carbon and nitrogen source. The enzyme has an Mr of 195 000±10 000 in its dimeric form with an Mr of 95 000±1000 for each subunit, a pH optimum at 5.4 in sodium citrate buffer, and does not require bivalent cations for its activity. Km values are 31.3±6.8 μM and 53.8±7.4 μM for Δ-1-pyrroline and NAD +, respectively. An inhibitory capacity for NADH is also shown using the purified enzyme. 相似文献
5.
Rat gastric mucosa was shown to contain a Mg 2+-dependent ATPase which is stimulated by HCO 3− at pH 8–9.Triton X-100 solubilizes this HCO 3−-stimulated, Mg 2+-dependent ATPase (ATP phosphohydrolase, EC 3.6.1.3).The gastric mucosa was resolved into five subcellular fractions by differential centrifugation. A large granule fraction (Fraction M), 28 000 g · min, was characterized by cytochrome c oxidase (marker enzyme for mitochondria). A microsomal fraction (Fraction P), 2 760 000 g · min, was characterized by 5′-nucleotidase(5′-ribonucleotide phosphohydrolase, EC 3.1.3.5) (plasma membrane).The Mg 2+-dependent ATPase was demonstrated to have a bimodal mitochondrial membranous localization: 24% of its activity is associated with cytochrome c oxidase, and 75% with 5′-nucleotidase(5′-ribonucleotide phosphohydrolase, EC 3.1.3.5) at pH 8.The HCO 3− addition resulted in two opposite effects: (1) a strong stimulation (84%) in Fraction M; (2) a slight inhibition (12%) in Fraction P.Fraction M was subfractionated by equilibration on a sucrose gradient. It gave rise to a homogeneous mitochondrial ( d, 1.17–1.21) Mg 2+-dependent ATPase, closely associated with cytochrome c oxidase. This ATPase is strongly stimulated ( ×2) by HCO 3−. The subfractionation of Fraction P gave rise to two distinct ATPases: (1) the major one is associated with membranous ( d, 1.10–1.15) material marked by 5′-nucleotidase and is slightly inhibited by HCO 3−; (2) the other is associated with denser ( d, 1.17–1.21) material and is stimulated by HCO 3−.The bicarbonate-stimulated fraction of the Mg 2+-dependent ATPase activity found in the gastric microsomal fraction is assumed to arise from mitochondrial cross-contamination. Further support comes from the optimal HCO 3− concentration. In addition, SCN − is shown to specifically inhibit the ATPase of Fraction M.From these results it appears that the implication of HCO 3−-stimulated ATPase in the gastric secretion of H + is not as clear as had been suggested. However, in the view of an ATPase-supported model for H + secretion, attention can be directed towards the Mg 2+-dependent ATPase found to be associated with microsomes. 相似文献
6.
Filamentous algae in eutrophic carp ponds in South Bohemia (Central Europe) were studied from 1988 to 1990. High biomass (490 g DW m -2) was attained by Cladophora fracta (O. F. Müll. ex Vahl) Kütz. after two months of growth. This marked growth depleted inorganic carbon in the water, but did not decrease the concentration of tissue nutrients. Laboratory measurements of final pH indicate that all the filamentous algae studied, except for Tribonema, are very efficient HCO 3
- users. An extremely high pH of 11.6 and oxygen concentration of 32 mg l -1 were measured in the algal mats. High pH resulted in CaCO 3 precipitation, visible as white incrustations on algal filaments. The amount of precipitated CaCO 3 reached 134 kg ha -1. After reaching peak biomass, 90% of the Cladophora decomposed over the next 95 days.The highest net photosynthetic rate in C. fracta was measured between pH range 8.5–10.0 and oxygen concentrations of 7–12 mg l -1. Optimum temperature for photosynthesis was between 17–22°C. 相似文献
7.
Summary Freshwater eel gills are notorious for their limited ability to pump chloride. As a result there is a considerable discrepancy between the Na + and Cl – plasma levels, and plasma HCO 3
– and blood pH are relatively high in this species.When eels are kept in tanks aerated with pure oxygen, significant alterations in blood acid-base balance, an increase in plasma pCO 2 and a decrease in blood pH, are observed. In fish studied after 3 weeks hyperoxia, the decrease in blood pH is compensated by an increase in plasma HCO 3
–. Such fish exhibit a Cl – influx 5 times higher than that observed in normoxic fish. This Cl – influx is readily inhibited by addition of SCN – to the external medium.An anion-stimulated ATPase activated by HCO 3
– and by Cl – and inhibited by SCN – was recently described in membrane fractions of the gills of Carassius auratus, a fish noted for its high Cl – pumping rate. This enzyme is also found in the gills of the eel. While the maximal rates of enzyme activation by HCO 3
– and by Cl – are similar in Carassius and Anguilla, the affinity of the enzyme for Cl – is 25 times higher in Carassius. In the microsomal fraction of the hyperoxic eel gills, the maximal anionstimulated ATPase activity remains unchanged but HCO 3
– affinity decreases by 50%, while Cl – affinity increases 5 times. Thus some characteristics of this ATPase seem to be closely related to the Cl – pump activity exhibited by the gill in fresh water. 相似文献
8.
Microbial carbonic anhydrase promotes carbonate deposition, which is important in the formation and evolution of global carbon cycle and geological processes. A kind of bacteria producing extracellular carbonic anhydrase was selected to study the effects of temperature, pH value and Ca 2+ concentration on bacterial growth, carbonic anhydrase activity and calcification rate in this paper. The results showed that the activity of carbonic anhydrase at 30 °C was the highest, which was beneficial to the calcification reaction, calcification rate of CaCO 3 was the fastest in alkaline environment with the initial pH value of 9.0. When the Ca2+ concentration was 60 mM, compared with other Ca 2+ concentration, CA bacteria could grow and reproduce best, and the activity of bacteria was the highest, too low Ca 2+ concentration would affect the generation of CaCO 3, while too high Ca 2+ concentration would seriously affect the growth of bacteria and reduce the calcification rate. Finally, the mechanism of CaCO 3 precipitation induced by microbial carbonic anhydrase was studied. Carbonic anhydrase can accelerate the hydration of CO 2 into HCO 3−, and react with OH − and Ca 2+ to form CaCO 3 precipitation in alkaline environment and in the presence of calcium source. 相似文献
9.
A study about the relationship between the physical–chemical parameters and the calcium carbonate balance between the haemolymph
fluid and mantle calcareous structures was carried out in Anodonta cygnea. An intense peak of HCO 3
− and a highest pH in December–January months may be understood as a preparation period for creating alkaline conditions. An
intense pH decrease from January to February in parallel with the HCO 3
− reduction seems to indicate the beginning process of carbonate precipitation. On the other hand, the following calcium and
HCO 3
− increases in February–May associated with a continuous and gradual pH fall profile may infer two combined aspects: calcium
and HCO 3
− absorption from external environment and a simultaneous intense calcium carbonate deposition in the haemolymph. So, the pCO 2 peak in this period reflects a subsequent result on equilibrium balance between HCO 3
− absorption and deposition. The only significant pO 2 increase in the next period, from February to June, is related with an energetic increase to support the metabolic activity
favouring the posterior intense pCO 2 peaks. The extended time of CO 2 production in the haemolymph from May to November should induce an increased metabolic acidosis with subsequent intense formation
of both HCO 3
− and Ca 2+ ions in the same period. This seems to result from CaCO 3 deposits dissolution in the haemolymph, the most direct calcareous source. Additionally, the later increase of metabolic
succinic acid during autumn may greatly potentiate this acidosis increasing the dissolution process. Consequently, the pH
profile present two simultaneous alkaline peaks in July and October, probably due to a strong HCO 3
− release from the CaCO 3 dissolution. So, the present seasonal results indicate that in the freshwater bivalve A. cygnea, the low metabolism with higher pH from the early winter is the main cause which may favour a calcareous precipitation, while
the high metabolism with lower pH from the early summer may function as an inductor of calcareous dissolution in the haemolymph. 相似文献
10.
The possibility of HCO 3− transport in the blue-green alga (cyanobacterium) Coccochloris peniocystis has been investigated. Coccochloris photosynthesized most rapidly in the pH range 8 to 10, where most of the inorganic C exists as HCO 3−. If photosynthesis used only CO 2 from the external solution the rate of photosynthesis would be limited by the rate of HCO 3− dehydration to CO 2. Observed rates of photosynthesis at alkaline pH were as much as 48-fold higher than could be supported by spontaneous dehydration of HCO 3− in the external solution. Assays for extracellular carbonic anhydrase were negative. The evidence strongly suggests that HCO 3− was a direct C source for photosynthesis. 相似文献
11.
Summary The replacement of carboxy-proton of IAA, plays an important role in the process of growth under saline conditions. Appreciable changes in pH have ben observed in the presence of CO 3
–2 and HCO 3
–, and increase in pH appears to be caused owing to the formation of unstable complex of IAA, which soon hydrolyzes and gives alkalinity. The pH change thus achieved favours IAA oxidase activity; therefore, suppression of growth is resulted in CO 3
–2 and HCO 3
– medium. In the presence of SO 4
–2 and Cl – salts slight lowering of pH takes place which does not favour IAA oxidase activity. It is therefore, presumed that anion (CO 3
–2, HCO 3
–, SO 4
–2 and Cl –) controls the process of growth and development through the alteration of pH of the medium. 相似文献
12.
The thermal coefficient of expansion of egg lecithin bilayer thickness, αd1, was measured as a function of its cholesterol content up to mole ratio lecithin/cholesterol of 1:1, and over the temperature range 0–40 °C. At all cholesterol contents αd1 changes abruptly at approximately 12 °C indicating a structural transition at this temperature. Above 12 °C, αd1 decreases monotonically from −2·10 −3 for pure egg lecithin to −1·10 –3 at mole ratio 1:1. Below 12 °C αd1 is walways higher than above 12 °C and shows a sharp, anomalously high value of −6·10 −3 at the mole ratio 2:1. The results have been interpreted as the movement of cholesterol into the bilayer or the formation of lecithin-cholesterol “complexes” at temperatures below 12 °C. Similar studies with phosphatidylinositol containing cholesterol showed no structural transition and lysolecithin containing cholesterol behaved differently giving two lamellar phases in equilibrium. 相似文献
13.
A comparative study of different derivatization procedures has been performed in order to improve the stability of the reaction products o-phthalaldehyde– N-acetylcysteine (OPA–NAC) polyamines. Procedures such as solution derivatization, solution derivatization followed by retention on a packing support, derivatization on different packing supports and on-column derivatization, have been optimized and compared. The degradation rate constant ( k) of the derivative was dependent on the procedure used and on the analyte. For the spermine (the most unstable isoindol tested) k was 8±2×10 −2 min −1 in solution versus 7.7±1.1×10 −4 min −1 on the (C 18) solid support. The results obtained showed that forming the derivative on the packing support (C 18) gave the best results following this procedure: conditioning the cartridges with borate buffer (1 ml, 0.5 M, pH 8), retention of the analyte, addition of 0.8 ml of OPA–NAC reagent, 0.2 ml borate buffer 0.8 M (pH 8) and elution of the isoindol with 3 ml of MeOH–borate buffer (9:1). The different derivatization procedures have been used to study the stability of the reaction products OPA–NAC polyamines formed in urine matrix using spermine as model compound. Similar results were obtained for standard solutions and urine samples. 相似文献
14.
Over recent years, the implementation of microbially produced calcium carbonate (CaCO3) in different industrial and environmental applications has become an alternative for conventional approaches to induce CaCO3 precipitation. However, there are many factors affecting the biomineralization of CaCO3, which may restrict its application. In this study, we investigated the effects of pH and aeration as the main two influential parameters on bacterial precipitation of CaCO3. The results showed that the aeration had a significant effect on bacterial growth and its rise from 0.5 to 4.5 SLPM could produce 4.2 times higher CaCO3 precipitation. The increase of pH to 12 resulted in 6.3-fold increase in CaCO3 precipitation as compared to uncontrolled-pH fermentation. Morphological characterization showed that the pH is an effective parameter on CaCO3 morphology. Calcite was found to be the predominant precipitate during aeration-controlled fermentations, while vaterite was mainly produced at lower pH (up to 10) over controlled-pH fermentations. Further increase in pH resulted in a morphological transition, and vaterite transformed to calcite at the pH ranges between 10 and 12. 相似文献
15.
A pH-sensitive glass electrode was used in a temperature-controlled stopped-flow rapid reaction apparatus to determine rates of pH equilibration in red cell suspensions. The apparatus requires less than 2 ml of reactants. The electrode is insensitive to pressure and flow variations, and has a response time of < 5 ms. A 20% suspension of washed fresh human erythrocytes in saline at pH 7.7 containing NaHCO 3 and extracellular carbonic anhydrase is mixed with an equal volume of 30 mM phosphate buffer at pH 6.7. Within a few milliseconds after mixing, extracellular HCO 3- reacts with H + to form CO 2, which enters the red cells and rehydrates to form HCO 3-, producing an electrochemical potential gradient for HCO 3- from inside to outside the cells. HCO 3- then leaves the cells in exchange for Cl -, and extracellular pH increases as the HCO 3- flowing out of the cells reacts with H +. Flux of HCO 3- is calculated from the dpH/d t during HCO 3--Cl - exchange, and a velocity constant is computed from the flux and the calculated intracellular and extracellular [HCO 3-]. The activation energy for the exchange process is 18.6 kcal/mol between 5°C and 17°C (transition temperature), and 11.4 kcal/mol from 17°C to 40°C. The activation energies and transition temperature are not significantly altered in the presence of a potent anion exchange inhibitor (SITS), although the fluxes are markedly decreased. These findings suggest that the rate-limiting step in red cell anion exchange changes at 17°C, either because of an alteration in the nature of the transport site or because of a transition in the physical state of membrane lipids affecting protein-lipid interactions. 相似文献
16.
Photosynthetic carbon uptake of the tropical seagrass Thalassia hemprichii (Ehrenb.) Aschers was studied by several methods. Photosynthesis in buffered seawater in media in the range of pH 6 to pH 9 showed an exponentially increasing rate with decreasing pH, thus indicating that free CO 2 was a photosynthetic substrate. However, these experiments were unable to determine whether photosynthesis at alkaline pH also contained some component due to HCO 3− uptake. This aspect was further investigated by studying photosynthetic rates in a number of media of varying pH (7.8-8.61) and total inorganic carbon (0.75-13.17 millimolar). In these media, photosynthetic rate was correlated with free CO 2 concentration and was independent of the HCO 3− concentration in the medium. Short time-course experiments were conducted during equilibration of free CO 2 and HCO 3− after injection of 14C labeled solution at acid or alkaline pH. High initial photosynthetic rates were observed when acidic solutions (largely free CO 2) were used but not with alkaline solutions. The concentration of free CO 2 was found to be a limiting factor for photosynthesis in this plant. 相似文献
17.
The present study explores the efficiency of Talaromyces thermophilus β-xylosidase, in the production of xylose and xylooligosaccharides. The β-xylosidase was immobilized by different methods namely ionic binding, entrapment and covalent coupling and using various carriers. Chitosan, pre-treated with glutaraldehyde, was selected as the best support material for β-xylosidase immobilization; it gave the highest immobilization and activity yields (94%, 87%, respectively) of initial activity, and also provided the highest stability, retaining 94% of its initial activity even after being recycled 25 times. Shifts in the optimal temperature and pH were observed for the immobilized β-xylosidase when compared to the free enzyme. The maximal activity obtained for the immobilized enzyme was achieved at pH 8.0 and 53 °C, whereas that for the free enzyme was obtained at pH 7.0 and 50 °C. The immobilized enzyme was more thermostable than the free β-xylosidase. We observed an increase of the Km values of the free enzyme from 2.37 to 3.42 mM at the immobilized state. Native and immobilized β-xylosidase were found to be stimulated by Ca 2+, Mn 2+ and Co 2+ and to be inhibited by Zn 2+, Cu 2+, Hg 2+, Fe 2+, EDTA and SDS. Immobilized enzyme was found to catalyze the reverse hydrolysis reaction, forming xylooligosaccharides in the presence of a high concentration of xylose. In order to examine the synergistic action of xylanase and β-xylosidase of T. thermophilus, these two enzymes were co-immobilized on chitosan. A continuous hydrolysis of 3% Oat spelt xylan at 50 °C was performed and better hydrolysis yields and higher amount of xylose was obtained. 相似文献
18.
Thermoalkaliphilic Bacillus sp. strain TAR-1 isolated from soil produced an extracellular xylanase. The enzyme (xylanase R) was purified to homogeneity by ammonium sulfate fractionation and anion-exchange chromatography. The molecular mass of xylanase R was 40 kDa and the isoelectric point was 4.1. The enzyme was most active over the range of pH 5.0 to 10.0 at 50°C. The optimum temperatures for activity were 75°C at pH 7.0 and 70°C at pH 9.0. Xylanase R was stable up to 65°C at pH 9.0 for 30 min in the presence of xylan. Mercury(ll) ion at 1 mM concentration abolished all the xylanase activity. The predominant products of xylan-hydrolysate were xylobiose, xylotriose, and higher oligosaccharides, indicating that xylanase R was an endo-acting enzyme. Xylanase R had a Km of 0.82 mg/ml and a Vmax of 280 μmol min −1 mg −1 for xylan at 50°C and pH 9.0. 相似文献
19.
The fragile histidine triad (Fhit) protein is a homodimeric protein with diadenosine 5′,5- P1, P3-triphosphate (Ap 3A) asymmetrical hydrolase activity. We have cloned the human cDNA Fhit in the pPROEX-1 vector and expressed with high yield in Escherichia coli with the sequence Met-Gly-His 6-Asp-Tyr-Asp-Ile-Pro-Thr-Thr followed by a rTEV protease cleavage site, denoted as “H6TV,” fused to the N-terminus of Fhit. Expression of H6TV–Fhit in BL21(DE3) cells for 3 h at 37°C produced 30 mg of H6TV–Fhit from 1 L of cell culture (4 g of cells). The H6TV–Fhit protein was purified to homogeneity in a single step, with a yield of 80%, using nickel-nitrilotriacetate resin and imidazole buffer as eluting agent. Incubation of H6TV–Fhit with rTEV protease at 4°C for 24 h resulted in complete cleavage of the H6TV peptide. There were no unspecific cleavage products. The purified Fhit protein could be stored for 3 weeks at 4°C without loss of activity. The pure protein was stable at −20°C for at least 18 months when stored in buffer containing 25% glycerol. Purified Fhit was highly active, with a Km value for Ap 3A of 0.9 μM and a kcat(monomer) value of 7.2 ± 1.6 s −1 ( n = 5). The catalytic properties of unconjugated Fhit protein and the H6TV–Fhit fusion protein were essentially identical. This indicates that the 24-amino-acid peptide containing the six histidines fused to the N-terminus of Fhit does not interfere in forming the active homodimers or in the binding of Ap 3A. 相似文献
20.
The species of inorganic carbon (CO 2 or HCO 3−) taken up a source of substrate for photosynthetic fixation by isolated Asparagus sprengeri mesophyll cells is investigated. Discrimination between CO 2 or HCO 3− transport, during steady state photosynthesis, is achieved by monitoring the changes (by 14C fixation) which occur in the specific activity of the intracellular pool of inorganic carbon when the inorganic carbon present in the suspending medium is in a state of isotopic disequilibrium. Quantitative comparisons between theoretical (CO 2 or HCO 3− transport) and experimental time-courses of 14C incorporation, over the pH range of 5.2 to 7.5, indicate that the specific activity of extracellular CO 2, rather than HCO 3−, is the appropriate predictor of the intracellular specific activity. It is concluded, therefore, that CO 2 is the major source of exogenous inorganic carbon taken up by Asparagus cells. However, at high pH (8.5), a component of net DIC uptake may be attributable to HCO 3− transport, as the incorporation of 14C during isotopic disequilibrium exceeds the maximum possible incorporation predicted on the basis of CO 2 uptake alone. The contribution of HCO 3− to net inorganic carbon uptake (pH 8.5) is variable, ranging from 5 to 16%, but is independent of the extracellular HCO 3− concentration. The evidence for direct HCO 3− transport is subject to alternative explanations and must, therefore, be regarded as equivocal. Nonlinear regression analysis of the rate of 14C incorporation as a function of time indicates the presence of a small extracellular resistance to the diffusion of CO 2, which is partially alleviated by a high extracellular concentration of HCO 3−. 相似文献
|