Phosphatase synthesis in Klebsiella (aerobacter) aerogenes growing in continuous culture

PhoN-expressing, lyophilized, recombinant Deinococcus radiodurans cells for uranium bioprecipitation

Employment of genetically engineered radiation resistant organisms to recover radionuclides/heavy metals from radioactive wastes is an attractive proposition. Cells of recombinant Deinococcus radiodurans strain expressing, a non-specific acid phosphatase encoding phoN gene, were lyophilized. Lyophilized recombinant Deinococcus cells retained viability and PhoN activity and could efficiently precipitate uranium from aqueous solutions for up to six months of storage at room temperature. Batch process for uranium removal using lyophilized cells was more efficient compared to a flow through system, in terms of percent uranium removed, substrate conservation and time taken. Lyophilized recombinant Deinococcus cells exhibited high loading of up to 5.7 g uranium/g dry weight of cells in a batch process at 20 mM input uranium concentration. Lyophilization deflated the cells but did not alter gross cell morphology or surface nucleation capability of cells for uranium precipitation. The precipitated uranyl phosphate remained tightly associated with the cell surface, thus facilitating easy recovery.

Enzymatic production of β-D-glucose-1-phosphate from trehalose

β-D-Glucose-1-phosphate (βGlc1P) is an efficient glucosyl donor for both enzymatic and chemical glycosylation reactions but is currently very costly and not available in large amounts. This article provides an efficient production method of βGlc1P from trehalose and phosphate using the thermostable trehalose phosphorylase from Thermoanaerobacter brockii. At the process temperature of 60 °C, Escherichia coli expression host cells are lysed and cell treatment prior to the reaction is, therefore, not required. In this way, the theoretical maximum yield of 26% could be easily achieved. Two different purification strategies have been compared, anion exchange chromatography or carbohydrate removal by treatment with trehalase and yeast, followed by chemical phosphate precipitation. In a next step, βGlc1P was precipitated with ethanol but this did not induce crystallization, in contrast to what is observed with other glycosylphosphates. After conversion of the product to its cyclohexylammonium salt, however, crystals could be readily obtained. Although both purification methods were quantitative (>99% recovery), a large amount of product (50%) was lost during crystallization. Nevertheless, a production process for crystalline βGlc1P is now available from the cheap substrates trehalose and inorganic phosphate.

Characterization of an ATP-regulated DNA-processing enzyme and thermotolerant phosphoesterase in the radioresistant bacterium Deinococcus radiodurans

A multiprotein DNA-processing complex identified from Deinococcus radiodurans exhibits uncharacterized ATP-sensitive nuclease functions. DR0505 was one of the 24 polypeptides identified from the complex. It contains two 5' nucleotidase motifs, one is at the C-terminal end of the N-terminal CPDD (calcineurin phosphodiesterase domain), with the second at the C-terminal end of the protein. Recombinant DR0505 showed both phosphomonoesterase and phosphodiesterase activities with chromogenic substrates, showing higher affinity for bis-(p-nitrophenyl) phosphate than for p-nitrophenyl phosphate. The enzyme exhibited pH optima ranging from 8.0 to 9.0 and metal-ion-dependent thermotolerance of esterase functions. Both mono- and di-esterase activities were stable at temperatures up to 50 °C in the presence of Mg2+, whereas monoesterase activity was observed at temperatures up to 80 °C in the presence of Mn2+ and up to 50 °C with Ca2+. The purified enzyme showed 5' nucleotidase activity on a wide range of natural mononucleotides including cyclic mononucleotides and 8-oxo-GMP. DR0505 showed a nearly 7-fold higher activity on ADP than AMP, but this activity was inhibited with ATP. Interestingly, DR0505 also showed single-stranded endonuclease and 3'→5' exonuclease activities on both single-stranded and double-stranded DNA-substrates. Unlike for the exonuclease activity, the single-stranded endonuclease activities observed on stem-loop substrates and at the single strand-double-strand junction in forked-hairpin substrates were not inhibited with ATP. These results suggested that DR0505 is an ATP-regulated DNA-processing enzyme and a thermotolerant esterase in vitro. We therefore suggest possible roles of this enzyme in nucleotide recycling and DNA processing, which is required for efficient double-strand break repair and the high radiation tolerance observed in D. radiodurans.

Radiation desiccation response motif-like sequences are involved in transcriptional activation of the Deinococcal ssb gene by ionizing radiation but not by desiccation

Single-stranded-DNA binding protein (SSB) levels during poststress recovery of Deinococcus radiodurans were significantly enhanced by (60)Co gamma rays or mitomycin C treatment but not by exposure to UV rays, hydrogen peroxide (H₂O₂), or desiccation. Addition of rifampin prior to postirradiation recovery blocked such induction. In silico analysis of the ssb promoter region revealed a 17-bp palindromic radiation/desiccation response motif (RDRM1) at bp -114 to -98 and a somewhat similar sequence (RDRM2) at bp -213 to -197, upstream of the ssb open reading frame. Involvement of these cis elements in radiation-responsive ssb gene expression was assessed by constructing transcriptional fusions of edited versions of the ssb promoter region with a nonspecific acid phosphatase encoding reporter gene, phoN. Recombinant D. radiodurans strains carrying such constructs clearly revealed (i) transcriptional induction of the ssb promoter upon irradiation and mitomycin C treatment but not upon UV or H₂O₂ treatment and (ii) involvement of both RDRM-like sequences in such activation of SSB expression, in an additive manner.

Purification, characterization, and gene cloning of glucose-1-phosphatase from Citrobacter braakii

Citrobacter braakii produced an intracellular acid glucose phosphatase (AgpC) which was purified 986 fold to homogeneity with the specific activity of 286 units/mg. AgpC hydrolyzed a wide variety of phosphorylated compounds with high activity for glucose-1-phosphate and glucose-6-phosphate. The optimum pH and temperature for the enzyme activity was pH 5.0 and 45 degrees C, respectively. The Km value for glucose-1-phosphate was 5.12 mM with a Vmax 27.8 U mg(-1). Its molecular weight was 46 kDa by SDS-PAGE gel and the sequence of N-terminal amino acid residues identified was Gln-Thr-Ala-Pro-Glu-Gly-Tyr-Gln-Leu-Gln. The glucose-1-phosphatase gene (agpC) was cloned from the C. braakii genomic library. This gene comprised 1,242 nucleotides and encoded a polypeptide of 413 amino acids. The result of its BLAST search showed a significant similarity with glucose-1-phosphatase from enterobacteria such as E. coli, Enterobacter, Shigella, and Salmonella.

Development and application of a screening assay for glycoside phosphorylases

Glycoside phosphorylases (GPs) are interesting enzymes for the glycosylation of chemical molecules. They require only a glycosyl phosphate as sugar donor and an acceptor molecule with a free hydroxyl group. Their narrow substrate specificity, however, limits the application of GPs for general glycoside synthesis. Although an enzyme's substrate specificity can be altered and broadened by protein engineering and directed evolution, this requires a suitable screening assay. Such a screening assay has not yet been described for GPs. Here we report a screening procedure for GPs based on the measurement of released inorganic phosphate in the direction of glycoside synthesis. It appeared necessary to inhibit endogenous phosphatase activity in crude Escherichia coli cell extracts with molybdate, and inorganic phosphate was measured with a modified phosphomolybdate method. The screening system is general and can be used to screen GP enzyme libraries for novel donor and acceptor specificities. It was successfully applied to screen a residue E649 saturation mutagenesis library of Cellulomonas uda cellobiose phosphorylase (CP) for novel acceptor specificity. An E649C enzyme variant was found with novel acceptor specificity toward alkyl beta-glucosides and phenyl beta-glucoside. This is the first report of a CP enzyme variant with modified acceptor specificity.

Cloning and overexpression of alkaline phosphatase PhoK from Sphingomonas sp. strain BSAR-1 for bioprecipitation of uranium from alkaline solutions

Cells of Sphingomonas sp. strain BSAR-1 constitutively expressed an alkaline phosphatase, which was also secreted in the extracellular medium. A null mutant lacking this alkaline phosphatase activity was isolated by Tn5 random mutagenesis. The corresponding gene, designated phoK, was cloned and overexpressed in Escherichia coli strain BL21(DE3). The resultant E. coli strain EK4 overexpressed cellular activity 55 times higher and secreted extracellular PhoK activity 13 times higher than did BSAR-1. The recombinant strain very rapidly precipitated >90% of input uranium in less than 2 h from alkaline solutions (pH, 9 +/- 0.2) containing 0.5 to 5 mM of uranyl carbonate, compared to BSAR-1, which precipitated uranium in >7 h. In both strains BSAR-1 and EK4, precipitated uranium remained cell bound. The EK4 cells exhibited a much higher loading capacity of 3.8 g U/g dry weight in <2 h compared to only 1.5 g U/g dry weight in >7 h in BSAR-1. The data demonstrate the potential utility of genetically engineering PhoK for the bioprecipitation of uranium from alkaline solutions.

Engineering of Deinococcus radiodurans R1 for bioprecipitation of uranium from dilute nuclear waste

Genetic engineering of radiation-resistant organisms to recover radionuclides/heavy metals from radioactive wastes is an attractive proposition. We have constructed a Deinococcus radiodurans strain harboring phoN, a gene encoding a nonspecific acid phosphatase, obtained from a local isolate of Salmonella enterica serovar Typhi. The recombinant strain expressed an approximately 27-kDa active PhoN protein and efficiently precipitated over 90% of the uranium from a 0.8 mM uranyl nitrate solution in 6 h. The engineered strain retained uranium bioprecipitation ability even after exposure to 6 kGy of 60Co gamma rays. The PhoN-expressing D. radiodurans offers an effective and eco-friendly in situ approach to biorecovery of uranium from dilute nuclear waste.

Acid phosphatase synthesis in Aspergillus flavus

Proteins with phosphatase activity were produced during the growth of Aspergillus flavus in a phosphate-supplemented liquid synthetic medium. The best carbon and nitrogen sources for the synthesis of phosphatase were glucose and ammonium sulfate, respectively. The proteins were separated by molecular exclusion and ion exclusion chromatography (IEC) into three components one of which showed phosphatase activity. The molar mass of the enzyme was approximately 62 kDa. The purified enzyme exhibited an optimum activity at pH 4.0 and at 45 degrees C. The activity of the enzyme was stimulated by Ca2+ and Mg2+ but inhibited by fluoride, iodoacetic acid, ethylenediaminetetraacetic acid and 2,4-dinitrophenol, and exhibited an apparent KM of approximately 420 mumol/L.

Phosphatase-mediated heavy metal accumulation by a Citrobacter sp. and related enterobacteria

A Citrobacter sp. was reported previously to accumulate heavy metals as cell-bound heavy metal phosphates. Metal uptake is mediated by the activity of a periplasmic acid-type phosphatase that liberates inorganic phosphate to provide the precipitant ligand for heavy metals presented to the cells. Amino acid sequencing of peptide fragments of the purified enzyme revealed significant homology to the phoN product (acid phosphatase) of some other enterobacteria. These organisms, together with Klebsiella pneumoniae, previously reported to produce acid phosphatase, were tested for their ability to remove uranium and lanthanum from challenge solutions supplemented with phosphatase substrate. The coupling of phosphate liberation to metal bioaccumulation was limited to the metal accumulating Citrobacter sp.; therefore the participation of species-specific additional factors in metal bioaccumulation was suggested.

Determination of mercapturic acid excretions in exposure control to toxicants

Toxicants can be converted in vivo by a variety of biotransformation reactions into substances that are more, equally, or less noxious than the parent compound. Although conjugation with glutathione is a process that usually results in less harmful products, these products might subsequently form new metabolites that exert more toxicity than the parent compound. These conjugation reactions are catalyzed by several classes of glutathione-S-transferase isoenzymes and thus result in the urinary or biliary excretion of N-acetyl-L-cysteine-S-conjugates (mercapturic acids). Inasmuch as GSH-S-transferase activity varies among different tissues, urinary excretion of mercapturic acids might reflect tissue-specific toxicity. Urinary mercapturic acids are biomarkers of internal and, in some cases, effective dose. The utility of these markers is, however, limited to times shortly after exposure. Studies on possible human deficiencies in some GSH-S-transferases might help us better understand interindividual variations in susceptibility to different toxicants and thus the differences in the pathway of mercapturic acid excretion pattern.

Phosphatase activity is a constant feature of all isolates of all major species of the family Enterobacteriaceae

In this study we evaluated phosphatase activity in members of the family Enterobacteriaceae by conventional methods and by a novel method. The novel method is based on the formation of bright-green-strained colonies by phosphatase-positive, but not phosphatase-negative, strains in the presence of a phosphate substrate, such as phenolphthalein monophosphate or 6-benzoylnaphthyl phosphate (6-BNP), and methyl green. A total of 1,055 strains belonging to 65 different species of Enterobacteriaceae were tested for green staining of the colonies in the presence of methyl green and either phenolphthalein monophosphate or 6-BNP and for phosphatase activity by three different conventional methods. With the sole exception of one Leminorella richardii type strain, all isolates of all of the species formed green-stained colonies in the presence of the substrate 6-BNP. All strains were phosphatase positive by all of the conventional methods.

Action of iron and iron-complexes on Klebsiella pneumoniae (Klebsiella aerogenes)

Iron In the Fe(III) oxidation state had a negligible effect on the growth of Klebsiella pneumoniae even at the highest concentration (0.45 mM) obtainable without precipitation in a minimal medium containing glucose and inorganic salts together with Tris as the buffer and glycerol 2-phosphate as the phosphorus source. Nevertheless in its presence the toxic action of Cd2+, Zn2+ and Cu2+ was antagonized while that of Co2+ and Ni2+ was potentiated. Higher iron levels were obtained by supplementing the minimal medium with fructose, glycine, gluconate, tartrate and citrate at a range of concentrations. With fructose and glycine all of the resulting solutions were red-brown and non-toxic. This was also found with the other complexing agents when the ligand:iron were low, but at higher ligand:iron ratios the solutions were green and toxic. Iron-citrate systems were especially toxic but resistance developed and was of the graded type. The results are discussed with particular reference to earlier physico-chemical studies by other workers and it is concluded that the red-brown colour is characteristic of the presence of polymers of high molar mass and that the green colour signifies the formation of low molar mass species.

Phosphate utilization and constitutive synthesis of phosphatases in Thermoactinomyces vulgaris Tsilinsky

Thermoactinomyces vulgaris utilized both organic and inorganic phosphates with equal efficiency for its growth. The specific activities of the thermophilic acid and alkaline phosphatases were found to be maximum at 1 mM concentration of each phosphate source. All the phosphatase isoenzymes (three alkaline and one acidic) were observed irrespective of the substrate source and concentration, suggesting constitutive synthesis of the enzymes. During growth and differentiation, both acid and alkaline phosphatases exhibited uniformly stable patterns of isoenzymes with slight variations in their specific activities.

Activity of some enzymes during growth and sporulation of Clostridium botulinum type E

The activities of alkaline and acid phosphatases, glucose dehydrogenase and NADH oxidase were assayed in cell-free extracts of sporogenic and asporogenic mutants of Clostridium botulinum. During growth of both mutants, the activities of alkaline and acid phosphatases were relatively constant, but during sporulation of the sporogenic mutant, the alkaline phosphatase activity rose to a maximum of 70 mumol/min x mg protein whereas the acid phosphatase decreased rapidly before it increased, indicating a possible role in sporogenesis. Glucose dehydrogenase activity was detected only in cell-free extracts of the sporogenic mutant and reached a maximum of 7 mumol/min x mg protein during the endospore maturation stage. The NADH oxidase activity was detected in both mutants. The NADH oxidase seems to stimulate glucose oxidation in both mutants during growth and the dehydrogenation processes of the butyric type of fermentation during spore formation in the sporogenic mutant. The findings suggest that increased glucose dehydrogenase activity in C. botulinum, as in Bacillus species, may serve as a spore event marker and that alkaline and acid phosphatases may play a regulatory role in anaerobic sporulation metabolism.

Hexokinase and glucose-phosphoenolpyruvate phosphotransferase synthesis in Klebsiella aerogenes strains growing in continuous culture

Considerable differences in steady-state hexokinase specific activity were found in 16 N.C.I.B. strains of Klebsiella aerogenes grown in identical conditions in glucose-limited chemostats. Strains of N.C.I.B. 8258 had no detectable activity, but its glucose-phosphoenolpyruvate phosphotransferase specific activity and that of the other strains were closely similar, and it is concluded that this phosphotransferase activity regulates the overall utilization of glucose, in which hexokinase plays no essential role. The hexokinase activity was subject to regulation by the availability of phosphorus, but this did not affect the glucose phosphotransferase activity. tlactose-grown organisms (including strain N.C.I.B. 8258) had no glucose phosphotransferase activity, but more than adequate hexokinase activity to phosphorylate the intracellularly liberated glucose.

Regulation of two phosphatases and a cyclic phosphodiesterase of Salmonella typhimurium

The regulation of three Salmonella typhimurium phosphatases in reponse to different nutritional limitations has been studied. Two enzymes, an acid hexose phosphatase (EC 3.1.3.2) and a cyclic phosphodiesterase (EC 3.1.4.d), appear to be regulated by the cyclic adenosine 3' ,5'-monophosphate (AMP) catabolite repression system. Levels of these enzymes increased in cells grown on poor carbon sources but not in cells grown on poor nitrogen or phosphorus sources. Mutants lacking adenyl cyclase did not produce elevated levels of these enzymes in response to carbon limitation unless cyclic AMP was supplied. Mutants lacking the cyclic AMP receptor protein did not produce elevated levels of these enzymes in response to carbon limitation regardless of the presence of cyclic AMP. Since no specific induction of either enzyme could be demonstrated, these enzymes appear to be controlled solely by the cyclic AMP system. Nonspecific acid phsphatase activity (EC 3.1.3.2) increased in response to carbon, nitrogen, phosphorus, or sulfur limitation. The extent of the increase depended on growth rate, with slower growth rates favoring greater increases, and on the type of limitation. Limitation for either carbon or phosphorus resulted in maximum increases, whereas severe limitation of Mg2+ caused only a slight increase. The increase in nonspecific acid phosphatase during carbon limitation was apparently not mediated by the catabolite repression system since mutants lacking adenyl cyclase or the cyclic AMP receptor protein still produced elevated levels of this enzyme during carbon starvation. Nor did the increase during phosphorus limitation appear to be mediated by the alkaline phosphatase regulatory system. A strain of Salmonella bearing a chromosomal mutation, which caused constitutive production of alkaline phosphatase (introduced by an episome from Escherichia coli), did not have constitutive levels of nonspecific acid phosphatase.

Properties of two phosphatases and a cyclic phosphodiesterase of Salmonella typhimurium

The properties of three phosphatases from Salmonella typhimurium have been examined. A cyclic 2',3'-nucleotide phosphodiesterase (EC 3.1.4.d) hydrolyzes cyclic 2',3'-purine and -pyrimidine nucleotides, as well as 3'-mononucleotides, and has a pH optimum of about 7.5. It requires divalent cations for activity and has a molecular weight of 67,000. Acid hexose phosphatase (EC 3.1.2.2) possesses activity towards hexose phosphates as well as other sugar phosphates. The enzyme is apparently a dimer of 37,000-dalton subunits. Nonspecific acid phosphatase (EC 3.1.3.2) hydrolyzes a variety of phosphate esters, including nucleotides and sugar phosphates. The enzyme also hydrolyzes the phosphoric anhydride bonds of pyrophosphate and nucleotides. Michaelis constants of the nonspecific acid phosphatase for several of its substrates are in the 1 to 2 mM range. Nonspecific acid phosphatase is a dimer of 27,000-dalton subunits.

Biosynthesis of mercapturic acids from allyl alcohol, allyl esters and acrolein

1. 3-Hydroxypropylmercapturic acid, i.e. N-acetyl-S-(3-hydroxypropyl)-l-cysteine, was isolated, as its dicyclohexylammonium salt, from the urine of rats after the subcutaneous injection of each of the following compounds: allyl alcohol, allyl formate, allyl propionate, allyl nitrate, acrolein and S-(3-hydroxypropyl)-l-cysteine. 2. Allylmercapturic acid, i.e. N-acetyl-S-allyl-l-cysteine, was isolated from the urine of rats after the subcutaneous injection of each of the following compounds: triallyl phosphate, sodium allyl sulphate and allyl nitrate. The sulphoxide of allylmercapturic acid was detected in the urine excreted by these rats. 3. 3-Hydroxypropylmercapturic acid was identified by g.l.c. as a metabolite of allyl acetate, allyl stearate, allyl benzoate, diallyl phthalate, allyl nitrite, triallyl phosphate and sodium allyl sulphate. 4. S-(3-Hydroxypropyl)-l-cysteine was detected in the bile of a rat dosed with allyl acetate.

The quantitative measurement of Alcian Blue-glycosaminoglycan complexes

1. A simple new quantitative micro method was developed to study the interaction of the cationic dye Alcian Blue 8GX and acid glycosaminoglycans under different conditions. After washing with ethanol the precipitated Alcian Blue-glycosaminoglycan complex was dissociated in Manoxol IB solution and the amount of bound dye measured spectrophotometrically. 2. Reaction profiles of complex-formation were determined in the presence of different concentrations of MgCl(2) at pH5.8, and could be used to study the critical electrolyte concentrations of glycosaminoglycans. At least 50mm-MgCl(2) was required to produce maximum precipitation of, and maximum uptake of, Alcian Blue by standard glycosaminoglycans. Maximum uptake of Alcian Blue by glycosaminoglycans in the urine of a patient with Hurler's syndrome required the presence of 25-50mm-MgCl(2). 3. Under standard conditions of maximum interaction, calibration curves for the quantitative determination of a series of standard glycosaminoglycans in 20mul volumes were nearly linear over the range 1-10mug. 4. The technique was used to determine the molecular binding ratios of Alcian Blue to glycosaminoglycans under controlled conditions.

The quantitative determination of glycosaminoglycans in urine with Alcian Blue 8GX

1. The effect of MgCl(2) concentration on the interaction of Alcian Blue 8GX and glycosaminoglycans in the urine of patients with mucopolysaccharidosis was studied by using a new quantitative micro method for the measurement of Alcian Blue-glycosaminoglycan complexes. This provided a means of measuring the critical electrolyte concentrations of urinary glycosaminoglycans. 2. Theoretical considerations based on the preceding paper (Whiteman, 1973) and experimental evidence provided here show that Alcian Blue 8GX may be used for the direct quantitative determination of total urinary glycosaminoglycans. The method is simple, requires sample volumes of 50mul or less, and gives results comparable with those obtained by other more complicated methods.