首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 78 毫秒
1.
Bacteria monitoring is essential for many industrial manufacturing processes, particularly those involving in food, biopharmaceuticals, and semiconductor production. Firefly luciferase ATP luminescence assay is a rapid and simple bacteria detection method. However, the detection limit of this assay for Escherichia coli is approximately 104 colony-forming units (CFU), which is insufficient for many applications. This study aims to improve the assay sensitivity by simultaneous conversion of PPi and AMP, two products of the luciferase reaction, back to ATP to form two chain-reaction loops. Because each consumed ATP continuously produces two new ATP molecules, this approach can achieve exponential amplification of ATP. Two consecutive enzyme reactions were employed to regenerate AMP into ATP: adenylate kinase converting AMP into ADP using UTP as the energy source, and acetate kinase catalyzing acetyl phosphate and ADP into ATP. The PPi-recycling loop was completed using ATP sulfurylase and adenosine 5′ phosphosulfate. The modification maintains good quantification linearity in the ATP luminescence assay and greatly increases its bacteria detection sensitivity. This improved method can detect bacteria concentrations of fewer than 10 CFU. This exponential ATP amplification assay will benefit bacteria monitoring in public health and manufacturing processes that require high-quality water.  相似文献   

2.
A new method for the rapid analysis of inorganic pyrophosphate (PPi) which utilizes the enzyme ATP sulfurylase is described. All components of the assay system are commercially available and inexpensive. The assay is linear over the range of 0.5–50.0 nmol of PPi and is not affected by inorganic phosphate. ATP and PPi can both be analyzed using this method.  相似文献   

3.
《FEBS letters》1987,224(2):348-352
It is possible to obtain synthesis of PPi by artifical ion potentials in Rhodospirillum rubrum chromatophores. PPi can be formed by K+-diffusion gradients (Δψ), H+ gradients (ΔpH) or a combination of both. In contrast, ATP can only be synthesized by imposed Δψ or Δψ+ΔpH. For ATP formation there is also a threshold value of K+ concentration below which synthesis of ATP is not possible. Such a threshold is not found for PPi formation. Both PPi and ATP syntheses are abolished by addition of FCCP or nigericin and only marginally affected by electron transport inhibitors. The synthesis of PPi can be monitored for several minutes before it ceases, while ATP production stops within 30 s. As a result the maximal yield of PPi is 200 nmol PPi/μmol BChl, while that of ATP is no more than 25 nmol ATP/μmol BChl. The initial rates of syntheses were 0.50 μmol PPi/μmol BChl per min and 2.0 μmol ATP/μmol per min, respectively. These rates are approx. 50 and 20% of the respective photophosphorylation rates under saturating illumination.  相似文献   

4.
《BBA》1986,851(2):276-282
Photosynthetic formation of inorganic pyrophosphate (PPi) in Rhodospirillum rubrum chromatophores has been studied utilizing a new and sensitive method for continuous monitoring of PPi synthesis. Studies of the reaction kinetics under a variety of conditions, e.g., at different substrate concentrations and different electron-transport rates, have been performed. At very low light intensities the rate of PPi synthesis is twice the rate of ATP synthesis. Antimycin A, at a concentration which strongly inhibited the photosynthetic ATP formation, inhibited the PPi synthesis much less. Even at low rates of electron transport a significant rate of PPi synthesis is obtained. The rate of photosynthetic ATP formation is stimulated up to 20% when PPi synthesis is inhibited. It is shown that PPi synthesis and ATP synthesis compete with each other. No inhibition of pyrophosphatase activity is observed at high carbonyl cyanide p-trifluoromethoxyhydrazone concentration while ATPase activity is strongly inhibited under the same conditions.  相似文献   

5.
An enzymatic assay for l-methionine was developed by coupling adenosylmethionine synthetase (AdoMetS) to a pyrophosphate (PPi) detection system, which was constructed using pyruvate, phosphate dikinase. To expand the use of this assay, the PPi detection system was embodied as three different forms, which allowed PPi to be measured by UV, visible, and fluorescent light detectors. The assay system was robust and could tolerate the addition of inorganic phosphate and ATP to the assay mixtures. l-Methionine could be accurately determined by coupling the PPi detection system and AdoMetS. This AdoMetS coupling assay was highly selective to l-methionine and exhibited no significant activity to other proteinaceous amino acids, ammonia, or urea, unlike conventional enzymatic assays for l-methionine. Spike and recovery tests showed that the AdoMetS assay could accurately and reproducibly determine increases in l-methionine in human plasma samples without any pretreatment to remove proteins and potentially interfering low-molecular-weight molecules. The high selectivity and robustness of the AdoMetS assay provide rapid and high-throughput analysis of l-methionine in various kinds of analytes.  相似文献   

6.
Phosphoenolpyruvate carboxykinase (PEPCK) is one of the pivotal enzymes that regulates the carbon flow of the central metabolism by fixing CO2 to phosphoenolpyruvate (PEP) to produce oxaloacetate or vice versa. Whereas ATP- and GTP-type PEPCKs have been well studied, and their protein identities are established, inorganic pyrophosphate (PPi)-type PEPCK (PPi-PEPCK) is poorly characterized. Despite extensive enzymological studies, its protein identity and encoding gene remain unknown. In this study, PPi-PEPCK has been identified for the first time from a eukaryotic human parasite, Entamoeba histolytica, by conventional purification and mass spectrometric identification of the native enzyme, followed by demonstration of its enzymatic activity. A homolog of the amebic PPi-PEPCK from an anaerobic bacterium Propionibacterium freudenreichii subsp. shermanii also exhibited PPi-PEPCK activity. The primary structure of PPi-PEPCK has no similarity to the functional homologs ATP/GTP-PEPCKs and PEP carboxylase, strongly suggesting that PPi-PEPCK arose independently from the other functional homologues and very likely has unique catalytic sites. PPi-PEPCK homologs were found in a variety of bacteria and some eukaryotes but not in archaea. The molecular identification of this long forgotten enzyme shows us the diversity and functional redundancy of enzymes involved in the central metabolism and can help us to understand the central metabolism more deeply.  相似文献   

7.
The growth of an anaerobic, spore-forming rod we have isolated from the cockroach gut after enrichment on media containing PPi was stimulated by the presence of PPi. The doubling time decreased and cell yield increased proportionately to PPi concentrations of up to 0.35%. A similar stimulation of the growth of Desulfotomaculum sp. by PPi has been reported. The PPi-stimulated Clostridium sp. fermented a number of sugars with the production of hydrogen, acetate, and butyrate, with smaller amounts of ethanol and butanol being produced from some substrates. The fermentation products were not qualitatively changed by the presence of PPi, but significantly more hydrogen was produced. The organism contained several of the enzymes previously reported from Entamoeba sp. and Propionibacterium sp., in which PPi serves as a source of a high-energy bond in place of ATP. These include significant amounts of pyruvate-phosphate dikinase and phosphoenolpyruvate carboxytransphosphorylase. The activities of many of the catabolic enzymes of the organism, as well as of its phosphatases and pyrophosphatase, were similar whether it was grown in the presence or absence of PPi. The organism did not accumulate intracellular polyphosphate granules but stored large amounts of glycogen.  相似文献   

8.
A simple method for measuring PPi at concentrations down to 2 μm has been devised using the ability of inorganic pyrophosphatase to be inactivated by fluoride in the presence of PPi. Orthophosphate (20 mm) and a number of other compounds did not interfere with the assay. The applicability of the method for direct measurement of PPi in urine is demonstrated.  相似文献   

9.
Acetate kinase, a member of the acetate and sugar kinase-Hsp70-actin (ASKHA) enzyme superfamily1-5, is responsible for the reversible phosphorylation of acetate to acetyl phosphate utilizing ATP as a substrate. Acetate kinases are ubiquitous in the Bacteria, found in one genus of Archaea, and are also present in microbes of the Eukarya6. The most well characterized acetate kinase is that from the methane-producing archaeon Methanosarcina thermophila7-14. An acetate kinase which can only utilize PPi but not ATP in the acetyl phosphate-forming direction has been isolated from Entamoeba histolytica, the causative agent of amoebic dysentery, and has thus far only been found in this genus15,16.In the direction of acetyl phosphate formation, acetate kinase activity is typically measured using the hydroxamate assay, first described by Lipmann17-20, a coupled assay in which conversion of ATP to ADP is coupled to oxidation of NADH to NAD+ by the enzymes pyruvate kinase and lactate dehydrogenase21,22, or an assay measuring release of inorganic phosphate after reaction of the acetyl phosphate product with hydroxylamine23. Activity in the opposite, acetate-forming direction is measured by coupling ATP formation from ADP to the reduction of NADP+ to NADPH by the enzymes hexokinase and glucose 6-phosphate dehydrogenase24.Here we describe a method for the detection of acetate kinase activity in the direction of acetate formation that does not require coupling enzymes, but is instead based on direct determination of acetyl phosphate consumption. After the enzymatic reaction, remaining acetyl phosphate is converted to a ferric hydroxamate complex that can be measured spectrophotometrically, as for the hydroxamate assay. Thus, unlike the standard coupled assay for this direction that is dependent on the production of ATP from ADP, this direct assay can be used for acetate kinases that produce ATP or PPi.  相似文献   

10.
Diel vertical migration by Heterosigma akashiwo (Hada) Hada (Raphidophyceae) was monitored in a 1.5 in tall microcosm. Vertical stratification, with low salinity and low orthophosphate (Pi) concentration in the upper layer and high salinity and high Pi concentration in the lower layer, was simulated in the tank, analogous to summer stratification in the Seto Inland Sea. The phosphate metabolism of H. akashiwo during this vertical migration was studied using 31P-NMR spectroscopy. At night this species migrated to the lower phosphate-rich layer and took up inorganic phosphate (Pi) which then was accumulated as polyphosphate (PPi) by an increase in the chain length of PPi During the daytime this species migrated to the phosphate-depleted surface water and utilized the accumulated PPi for photophosphorylation by decreasing the chain length of PPi During the first night after the phosphorus was introduced to the previously impoverished waters, the cells took up inorganic phosphate, accumulating the new phosphorus nutrient internally as Pi But the cells did not convert Pi to PPi presumably due to their lack of ATP. After the second day of the experiment, conversion of Pi to PPi at night was much more rapid than on the first day, presumably due to increased ATP availability. Then the cycle continued, with uptake of Pi and conversion to PPi at night at the bottom and its utilization during the day at the surface. These data suggest that the role of PPi in the metabolism of this species appears to be as a phosphate pool which regulates the level of Pi and ATP in the cell. Diel vertical migration allows this red tide species to shuttle between the phosphate-rich lower layer and the photic upper layer in stratified waters. 31P-NMR is shown to be a valuable tool in studying the phosphorus metabolism in migrating organisms.  相似文献   

11.
The effect of pyrophosphate (PPi) on labeled nucleotide incorporation into noncatalytic sites of chloroplast ATP synthase was studied. In illuminated thylakoid membranes, PPi competed with nucleotides for binding to noncatalytic sites. In the dark, PPi was capable of tight binding to noncatalytic sites previously vacated by endogenous nucleotides, thereby preventing their subsequent interaction with ADP and ATP. The effect of PPi on ATP hydrolysis kinetics was also elucidated. In the dark at micromolar ATP concentrations, PPi inhibited ATPase activity of ATP synthase. Addition of PPi to the reaction mixture at the step of preliminary illumination inhibited high initial activity of the enzyme, but stimulated its activity during prolonged incubation. These results indicate that the stimulating effect of PPi light preincubation with thylakoid membranes on ATPase activity is caused by its binding to ATP synthase noncatalytic sites. The inhibition of ATP synthase results from competition between PPi and ATP for binding to catalytic sites. Published in Russian in Biokhimiya, 2009, Vol. 74, No. 7, pp. 956–962.  相似文献   

12.
The co-ordinated action of the two proton-transporting enzymes at the tonoplast of the CAM plants. daigremontiana, viz. the ATPase and the PPiase, was studied by measuring fluorescent dye quenching. The initial rates of ATP and PPi-dependent H+ transport into tonoplast vesicles were additive, i.e. the sum of the rates obtained with each substrate alone was in the range obtained with both substrates added together at the same time. Conversely, the activities of the two H+ pumps were non-additive in establishing the steady-state level, indicating that the final steady state was under thermodynamic control of a maximal attainable proton gradient. The initial rates of ATP-dependent H+ transport were stimulated enormously if ATP was added a few minutes after pre-energization of the vesicles with PPi. This stimulation was observed only when the PPiase was active. A similar effect was not found for PPi-dependent H+ transport after pre-energization with ATP. Hence, a PPiase-activated ATP-dependent H+ transport can be distinguished from the basic ATP- and the basic PPi-dependent H+ transport. In parallel a PPi-dependent stimulation of ATP hydrolysis in the absence of ionophores was measured, which can only be attributed to the activity of the PPiase. PPiase-activated ATP-dependent H+ transport depends on the presence of permeant anions. It shows properties of both H+ transport activities, i.e. the chloride and malate stimulation and the DCCD inhibition of the ATP-dependent H+ transport activity, the nitrate stimulation and the KF inhibition of the PPi-dependent H+ transport activity. Only MgPPi and MgATP were effective as the respective substrates. The PPiase-activated ATP-dependent H+ transport had a half life of about 5–9 minutes. It is concluded that the PPiase may play an important role in kinetic regulation of the ATPase, and implications for CAM metabolism are discussed.  相似文献   

13.
Entamoeba histolytica, an amitochondriate protozoan parasite that relies on glycolysis as a key pathway for ATP generation, has developed a unique extended PPi-dependent glycolytic pathway in which ADP-forming acetyl-coenzyme A (CoA) synthetase (ACD; acetate:CoA ligase [ADP-forming]; EC 6.2.1.13) converts acetyl-CoA to acetate to produce additional ATP and recycle CoA. We characterized the recombinant E. histolytica ACD and found that the enzyme is bidirectional, allowing it to potentially play a role in ATP production or in utilization of acetate. In the acetate-forming direction, acetyl-CoA was the preferred substrate and propionyl-CoA was used with lower efficiency. In the acetyl-CoA-forming direction, acetate was the preferred substrate, with a lower efficiency observed with propionate. The enzyme can utilize both ADP/ATP and GDP/GTP in the respective directions of the reaction. ATP and PPi were found to inhibit the acetate-forming direction of the reaction, with 50% inhibitory concentrations of 0.81 ± 0.17 mM (mean ± standard deviation) and 0.75 ± 0.20 mM, respectively, which are both in the range of their physiological concentrations. ATP and PPi displayed mixed inhibition versus each of the three substrates, acetyl-CoA, ADP, and phosphate. This is the first example of regulation of ACD enzymatic activity, and possible roles for this regulation are discussed.  相似文献   

14.
The preincubation of rat liver crude extracts with ATP caused a 60% inactivation of phosphoprotein phosphatase in 30 min at 30 °C. The presence of Mg2+, or cyclic AMP, along with ATP in the preincubation mixture had no effect on the inactivation of phosphatase caused by ATP. The crude liver phosphatase was also inactivated by ADP or PPi; PPi being the most potent inactivating metabolite. AMP, adenosine or Pi were without any effect. The effect of ATP or PPi was completely reversed by cobalt. The cobalt effect was very specific and could not be replaced by several metal ions tested except by Mn2+ which was partly active. With the aid of sucrose density gradient studies, it was also shown that PPicauses an apparent conversion of a 4.1 S form to a 7.8 S form of the enzyme in rat liver extracts. Cobalt, on the other hand, converts the higher 7.8 S form to a lower 4.1 S form of the enzyme. The preincubation of purified rabbit liver phosphoprotein phosphatase with PPi also caused a complete inactivation of the enzyme in 40 min. The inactivation of the enzyme by PPi was completely reversed by cobalt. Unlike the apparent interconversion between different molecular forms of the enzyme by PPi and cobalt in rat liver crude extracts, no such interconversion of purified rabbit liver phosphoprotein phosphatase was observed in the presence of PPi and cobalt.  相似文献   

15.
The efflux of mitochondrial adenine nucleotide which is induced by addition of PPi to suspensions of rat liver mitochondria has been investigated. This efflux of adenine nucleotide is greatly stimulated by the uncoupler FCCP at 1 μM, Vmax being 6.7 nmol/min per mg protein as compared to 2.0 nmol/min per mg protein in its absence. The depletion process is inhibited by carboxyatractyloside. The Km for PPi of 1.25 mM is essentially unchanged when uncoupler is added. Quantitation of the individual adenine nucleotide species (ATP, ADP and AMP) and their relationship to the rate of efflux suggests that ADP is the predominant species being exchanged for PPi.  相似文献   

16.
An enzyme from Entamoeba histolytica catalyzes the formation of acetyl phosphate and orthophosphate from acetate and inorganic pyrophosphate (PPi), but it displays much greater activity in the direction of acetate formation. It has been purified 40-fold and separated from interfering enzyme activities by chromatography. Its reaction products have been quantitatively established. ATP cannot replace PPi as phosphoryl donor in the direction of acetyl phosphate formation nor will any common nucleoside diphosphate replace orthophosphate as phosphoryl acceptor in the direction of acetate formation. The trivial name proposed for the new enzyme is acetate kinase (PPi).  相似文献   

17.
Although the capacity of isolated β-subunits of the ATP synthase/ATPase to perform catalysis has been extensively studied, the results have not conclusively shown that the subunits are catalytically active. Since soluble F1 of mitochondrial H+-ATPase can bind inorganic pyrophosphate (PPi) and synthesize PPi from medium phosphate, we examined if purified His-tagged β-subunits from Thermophilic bacillus PS3 can hydrolyze PPi. The difference spectra in the near UV CD of β-subunits with and without PPi show that PPi binds to the subunits. Other studies show that β-subunits hydrolyze [32P] PPi through a Mg2+-dependent process with an optimal pH of 8.3. Free Mg2+ is required for maximal hydrolytic rates. The Km for PPi is 75 μM and the Vmax is 800 pmol/min/mg. ATP is a weak inhibitor of the reaction, it diminishes the Vmax and increases the Km for PPi. Thus, isolated β-subunits are catalytically competent with PPi as substrate; apparently, the assembly of β-subunits into the ATPase complex changes substrate specificity, and leads to an increase in catalytic rates.  相似文献   

18.
The catabolism of ATP and other nucleotides participates partly in the important function of nucleotide salvage by activated cells and also in removal or de novo generation of compounds including ATP, ADP, and adenosine that stimulate purinergic signaling. Seven nucleotide pyrophosphatase/phosphodiesterase NPP family members have been identified to date. These isoenzymes, related by up conservation of catalytic domains and certain other modular domains, exert generally non-redundant functions via distinctions in substrates and/or cellular localization. But they share the capacity to hydrolyze phosphodiester or pyrophosphate bonds, though generally acting on distinct substrates that include nucleoside triphosphates, lysophospholipids and choline phosphate esters. PPi generation from nucleoside triphosphates, catalyzed by NPP1 in tissues including cartilage, bone, and artery media smooth muscle cells, supports normal tissue extracellular PPi levels. Balance in PPi generation relative to PPi degradation by pyrophosphatases holds extracellular PPi levels in check. Moreover, physiologic levels of extracellular PPi suppress hydroxyapatite crystal growth, but concurrently providing a reservoir for generation of pro-mineralizing Pi. Extracellular PPi levels must be supported by cells in mineralization-competent tissues to prevent pathologic calcification. This support mechanism becomes dysregulated in aging cartilage, where extracellular PPi excess, mediated in part by upregulated NPP1 expression stimulates calcification. PPi generated by NPP1modulates not only hydroxyapatite crystal growth but also chondrogenesis and expression of the mineralization regulator osteopontin. This review pays particular attention to the role of NPP1-catalyzed PPi generation in the pathogenesis of certain disorders associated with pathologic calcification.  相似文献   

19.
Flux into the glycolytic pathway of most cells is controlled via allosteric regulation of the irreversible, committing step catalyzed by ATP-dependent phosphofructokinase (PFK) (ATP-PFK; EC 2.7.1.11), the key enzyme of glycolysis. In some organisms, the step is catalyzed by PPi-dependent PFK (PPi-PFK; EC 2.7.1.90), which uses PPi instead of ATP as the phosphoryl donor, conserving ATP and rendering the reaction reversible under physiological conditions. We have determined the enzymic properties of PPi-PFK from the anaerobic, hyperthermophilic archaeon Thermoproteus tenax, purified the enzyme to homogeneity, and sequenced the gene. The ∼100-kDa PPi-PFK from T. tenax consists of 37-kDa subunits; is not regulated by classical effectors of ATP-PFKs such as ATP, ADP, fructose 2,6-bisphosphate, or metabolic intermediates; and shares 20 to 50% sequence identity with known PFK enzymes. Phylogenetic analyses of biochemically characterized PFKs grouped the enzymes into three monophyletic clusters: PFK group I represents only classical ATP-PFKs from Bacteria and Eucarya; PFK group II contains only PPi-PFKs from the genus Propionibacterium, plants, and amitochondriate protists; whereas group III consists of PFKs with either cosubstrate specificity, i.e., the PPi-dependent enzymes from T. tenax and Amycolatopsis methanolica and the ATP-PFK from Streptomyces coelicolor. Comparative analyses of the pattern of conserved active-site residues strongly suggest that the group III PFKs originally bound PPi as a cosubstrate.As first discovered in Entamoeba histolytica (27), in some members of all three domains of life (Bacteria, Eucarya, and Archaea), the first committing step of glycolysis, the phosphorylation of fructose 6-phosphate (Fru 6-P), is catalyzed not by common ATP-dependent phosphofructokinase (PFK) (ATP-PFK; EC 2.7.1.11) but by an enzyme which uses PPi as a phosphoryl donor (PPi-PFK; EC 2.7.1.90) (2234). The only archaeal PPi-PFK described so far is the enzyme of Thermoproteus tenax, a hyperthermophilic, anaerobic archaeon which is able to grow chemolithotrophically with CO2, H2, and S0, as well as chemo-organothrophically in the presence of S0 and carbohydrates (11, 41). As shown by enzymatic and in vivo studies (pulse-labeling experiments), T. tenax metabolizes glucose mainly via a variation of the Embden-Meyerhof-Parnas pathway distinguished by the reversible PPi-PFK reaction (34, 35).In contrast to the virtually irreversible reaction catalyzed by the ATP-PFK, the phosphorylation by PPi is reversible. Thus, for thermodynamic reasons, the PPi-PFK should be able to replace the enzymes of both the forward (ATP-PFK) and reverse (fructose-bisphosphatase [FBPase]) reactions. Consistent with the presumed bivalent function of the PPi-dependent enzyme, in prokaryotes and parasitic protists which possess PPi-PFK, little, if any, ATP-PFK or FBPase activity is present. Strikingly, the PPi-PFKs of these organisms proved to be nonallosteric, suggesting that the control of the carbon flux through the pathway is no longer exerted by the PFK in these organisms. A considerably different situation has been described for higher plants and the green alga Euglena gracilis, showing comparable ATP-PFK, FBPase, and PPi-PFK activities and allosteric regulation of their PPi-dependent enzyme by fructose 2,6-bisphosphate (12, 22). However, in most cases it is not obvious which physiological role PPi-PFK performs: reversible catalysis of glycolysis/gluconeogenesis, increase of the energy yield of glycolysis under certain conditions in which the energy charge is low, or ATP-conservation in obligately fermentative organisms (22).Closely related to questions concerning the biological function of PPi-PFKs is the matter of their evolutionary origin: are these enzymes the result of a secondary adaptation from ATP-PFKs, or do they represent an original phenotype, as suggested by their specificity for PPi, which is thought to be an ancient source of metabolic energy (9, 18, 19, 26). Indicated by sequence similarity (3, 4), all known PPi- and ATP-PFKs are homologous and therefore originated from a common ancestral root. From more recent studies of Streptomyces coelicolor PFK (4), the previous assumption of a single event which separated PPi- and ATP-PFKs had to be revised in favor of a multiple differentiation, leaving open, however, the question of the primary or secondary origin of PPi-PFK.Understanding of PFK evolution has been impaired by a lack of knowledge concerning archaeal PFK, although the existence of ATP-PFK (31), PPi-PFK (34), and also ADP-dependent PFK (16, 31) in Archaea has been described. To address the evolution of PFK, we describe the PPi-PFK from T. tenax and compare its sequence and structure to those of known bacterial and eucaryal PFK enzymes.  相似文献   

20.
A generally applicable, inexpensive, and sensitive method for the determination of inorganic pyrophosphate (PPi) was developed. PPi was quantitatively separable from solution even in nanomolar concentrations by filtration through a membrane filter in the presence of CaCl2 and KF. The separated PPi was dissolved by immersing the filter in 0.5 n H2SO4. Inorganic phosphate (Pi) was removed by precipitating it as a phosphomolybdate-triethylamine complex and the PPi was measured as a green pyrophosphomolybdate in the presence of 2-mercaptoethanol. Nucleotides and phosphate esters do not react. PPi can be accurately assayed even when there is a 104-fold excess of Pi. Trimetaphosphate, tripolyphosphate, and tetrapolyphosphate also give this green color, but the rate of the color formation is 50 times slower than that with PPi. Thus this interference of the polyphosphates can be eliminated or the polyphosphates can be assayed simultaneously with the PPi in the same sample.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号