Do bacterial L-asparaginases utilize a catalytic triad Thr-Tyr-Glu?

The structures of Erwinia chrysanthemi L-asparaginase (ErA) complexed with the L- and D-stereoisomers of the suicide inhibitor, 6-diazo-5-oxy-norleucine, have been solved using X-ray crystallography and refined with data extending to 1.7 A. The distances between the Calpha atoms of the inhibitor molecules and the hydroxyl oxygen atoms of Thr-15 and Tyr-29 (1.20 and 1.60 A, respectively) clearly indicate the presence of covalent bonds between these moieties, confirming the nucleophilic role of Thr-15 during the first stage of enzymatic reactions and also indicating direct involvement of Tyr-29. The factors responsible for activating Tyr-29 remain unclear, although some structural changes around Ser-254', Asp-96, and Glu-63, common to both complexes, suggest that those residues play a function. The role of Glu-289' as the activator of Tyr-29, previously postulated for the closely related Pseudomonas 7A L-glutaminase-asparaginase, is not confirmed in this study, due to the lack of interactions between these residues in these complexes and in holoenzymes. The results reported here are consistent with previous reports that mutants of Escherichia coli L-asparaginase lacking Glu-289 remain catalytically active and prove the catalytic roles of both Thr-15 and Tyr-29, while still leaving open the question of the exact mechanism resulting in the unusual chemical properties of these residues.

Comparison of intramuscular therapy with Erwinia asparaginase and asparaginase Medac: pharmacokinetics, pharmacodynamics, formation of antibodies and influence on the coagulation system

Asparaginase comes from different biological sources and the various preparations have different pharmacokinetic properties, and their tendency to induce side-effects is different. Erwinia asparaginase (ASNase) has a shorter half-life than the Escherichia coli preparations, and it has been reported to be less immunogenic than the E. coli preparations and to induce fewer coagulation disorders. Children with newly diagnosed acute lymphoblastic leukaemia (ALL) were included in this study. Twenty-seven patients were treated with Erwinia ASNase (induction therapy 30.000 IU/m2/d i.m. for 10 d, and re-induction therapy 30.000 IU/m2 twice a week for 2 weeks) and 15 were treated with ASNase Medac (induction therapy 1.000 IU/m2/d i.m. for 10 d, and re-induction therapy 5.000 IU/m2 i.m. twice a week for 2 weeks). Blood samples were drawn to determine enzyme activity, l-asparagine, anti-asparaginase antibodies, and coagulation parameters. After i.m. administration, Erwinia ASNase displayed a protracted absorption phase compared to ASNase Medac. The mean bioavailability after i.m. administration was 27% for Erwinia ASNase and 45% for ASNase Medac respectively. Mean trough enzyme activities during induction therapy were Erwinia ASNase 1748 IU/l and ASNase Medac 272 IU/l, and during re-induction therapy Erwinia ASNase 83 IU/l and ASNase Medac 147 IU/l. We conclude that in this setting, therapy with ASNase Medac resulted in sufficient treatment during both phases of therapy, whereas treatment with Erwinia ASNase resulted in unnecessarily intense therapy during the induction phase and insufficient treatment during the re-induction phase. There was no significant difference in the incidence of antibody formation, and therapy with Erwinia ASNase resulted in a more pronounced influence on the coagulation parameters than therapy with ASNase Medac.

Expression of a mineral phosphate solubilizing gene from Erwinia herbicola in two rhizobacterial strains

A genetic construction was carried out using the broad host range vector pKT230 and plasmid pMCG898, which encodes the Erwinia herbicola pyrroloquinoline quinone (PQQ) synthase, a gene involved in mineral phosphate solubilization (mps). The final construction was transformed and expressed in Escherichia coli MC1061, and the recombinant plasmids were transferred to Burkholderia cepacia IS-16 and Pseudomonas sp. PSS recipient cells by conjugation. Clones containing recombinant plasmids produced higher clearing halos in plates with insoluble phosphate as the unique (P) source, in comparison with those of strains without plasmids, demonstrating the heterologous expression of the E. herbicola gene in the recipient strains. This genetic manipulation allowed the increase in mps ability of both strains, enhancing their potentialities as growth promoters of agricultural crops. These results represent the first report on the application of the recombinant DNA methodology for the obtaining of improved phosphate solubilizing ability from rhizobacterial strains for biofertilization purposes.

Pharmacokinetics of Erwinia asparaginase after intravenous and intramuscular administration

PURPOSE

To describe the pharmacokinetics of Erwinia asparaginase (ASNase) after intravenous (i.v.) and intramuscular (i.m.) administration.

METHODS

A group of 29 children with newly diagnosed acute lymphoblastic leukemia (ALL) received Erwinia ASNase 30,000 IU/m2 every day for 10 days during multiagent induction therapy. Of these patients. 13 received i.v. therapy and 16 received i.m. therapy. During the reinduction phase the patients received Erwinia ASNase 30,000 IU/m2 twice a week for 2 weeks (Mondays and Thursdays) (8 patients in the i.v.-treated group and 11 patients in the i.m.-treated group). ASNase activity (spectrophotometric assay) was measured in plasma samples obtained from the patients at various times during therapy.

RESULTS

The estimated half-life was 6.4 +/- 0.5 h (n = 13), the absorption rate after i.m. administration was found to limit elimination. The apparent volume of distribution corresponded well with the volume of plasma. The estimated clearance suggested that Erwinia ASNase is a low-clearance drug. Bioavailability after i.m. administration was (mean +/- SEM) 27.0 +/- 4.5% (range 11-61%; n = 12).

CONCLUSIONS

In this study the pharmacokinetic parameters after i.v. and i.m. administration of Erwinia ASNase were determined based on a substantial number of patients. The present findings emphasize the importance of conducting proper pharmacokinetic studies before a new drug or a new preparation of a drug is introduced in a different schedule.

Cloning and characterization of the gene cluster for palatinose metabolism from the phytopathogenic bacterium Erwinia rhapontici

Erwinia rhapontici is able to convert sucrose into isomaltulose (palatinose, 6-O-alpha-D-glucopyranosyl-D-fructose) and trehalulose (1-O-alpha-D-glucopyranosyl-D-fructose) by the activity of a sucrose isomerase. These sucrose isomers cannot be metabolized by plant cells and most other organisms and therefore are possibly advantageous for the pathogen. This view is supported by the observation that in vitro yeast invertase activity can be inhibited by palatinose, thus preventing sucrose consumption. Due to the lack of genetic information, the role of sucrose isomers in pathogenicity has not been evaluated. Here we describe for the first time the cloning and characterization of the palatinose (pal) genes from Erwinia rhapontici. To this end, a 15-kb chromosomal DNA fragment containing nine complete open reading frames (ORFs) was cloned. The pal gene products of Erwinia rhapontici were shown to be homologous to proteins involved in uptake and metabolism of various sugars from other microorganisms. The palE, palF, palG, palH, palK, palQ, and palZ genes were oriented divergently with respect to the palR and palI genes, and sequence analysis suggested that the first set of genes constitutes an operon. Northern blot analysis of RNA extracted from bacteria grown under various conditions implies that the expression of the palI gene and the palEFGHKQZ genes is oppositely regulated at the transcriptional level. Genes involved in palatinose uptake and metabolism are down regulated by sucrose and activated by palatinose. Palatinose activation is inhibited by sucrose. Functional expression of palI and palQ in Escherichia coli revealed sucrose isomerase and palatinase activity, respectively.

Heterogeneous transcription of an indoleacetic acid biosynthetic gene in Erwinia herbicola on plant surfaces

We investigated the spatial pattern of expression of ipdC, a plant inducible gene involved in indoleacetic acid biosynthesis in Erwinia herbicola, among individual cells on plants to gain a better understanding of the role of this phenotype in the epiphytic ecology of bacteria and the factors involved in the regulation of ipdC. Nonpathogenic E. herbicola strain 299R harboring a transcriptional fusion of ipdC to gfp was inoculated onto bean plants, recovered from individual leaves 48 h after inoculation, and subjected to fluorescence in situ hybridization using a 16S rRNA oligonucleotide probe specific to strain 299R. Epifluorescence images captured through a rhodamine filter were used to distinguish the 5carboxytetramethylrhodamine-labeled cells of strain 299R from other leaf microflora. Quantification of the green fluorescence intensity of individual cells by analysis of digital images revealed that about 65% of the 299R cells recovered from bean leaves had higher ipdC expression than in culture. Additionally, 10% of the cells exhibited much higher levels of green fluorescence than the median fluorescence intensity, indicating that they are more heterogeneous with respect to ipdC expression on plants than in culture. Examination of 299R cells in situ on leaf surfaces by confocal laser scanning microscopy after fluorescence in situ hybridization of cells on leaf samples showed that even cells that were in close proximity exhibited dramatically different green fluorescence intensities, and thus, were in a physical or chemical microenvironment that induced differential expression of ipdC.

Quenching of singlet oxygen by carotenoids produced in escherichia coli - attenuation of singlet oxygen-mediated bacterial killing by carotenoids

We examined the viability of Escherichia coli transformants harboring various carotenoids synthesizing genes in a medium containing an enzymatic singlet oxygen generating system, which contained myeloperoxidase, hydrogen peroxide and Br(-) at pH 4.5. Singlet oxygen quenching activities of various carotenoids in phosphatidyl choline micelles in aqueous media were also studied using the same enzymatic singlet oxygen generating system. Viability of the transformants producing carotenoids was higher than that of the wild type E. coli in the singlet oxygen generation mixture. Of the transformants tested, the viability of zeaxanthin-diglucoside producing transformant was the highest. Carotenoids in increasing order of k(q) values were beta-carotene, a cyclic carotene<zeaxanthin with hydroxy groups < or =lycopene, an acyclic carotene<canthaxanthin and astaxanthin with keto groups <<zeaxanthin-diglucoside. The k(q) value of zeaxanthin-diglucoside was 3.5 times higher than that of beta-carotene. These results suggest that orientation of the carotenoids in lipid layers of micelles and also in phospholipid membrane of bacteria is important for quenching of singlet oxygen. Furthermore, the viability of transformants producing lycopene and phytoene was almost as high as that of the transformant producing zeaxanthin-glucoside.

Cloning and random mutagenesis of the Erwinia herbicola tyrR gene for high-level expression of tyrosine phenol-lyase

Tyrosine phenol-lyase (Tpl), which can synthesize 3, 4-dihydroxyphenylalanine from pyruvate, ammonia, and catechol, is a tyrosine-inducible enzyme. Previous studies demonstrated that the tpl promoter of Erwinia herbicola is activated by the TyrR protein of Escherichia coli. In an attempt to create a high-Tpl-expressing strain, we cloned the tyrR gene of E. herbicola and then randomly mutagenized it. Mutant TyrR proteins with enhanced ability to activate tpl were screened for by use of the lac reporter system in E. coli. The most increased transcription of tpl was observed for the strain with the mutant tyrR allele involving amino acid substitutions of alanine, cysteine, and glycine for valine-67, tyrosine-72, and glutamate-201, respectively. A tyrR-deficient derivative of E. herbicola was constructed and transformed with a plasmid carrying the mutant tyrR allele (V67A Y72C E201G substitutions). The resultant strain expressed Tpl without the addition of tyrosine to the medium and produced as much of it as was produced by the wild-type strain grown under tyrosine-induced conditions. The regulatory properties of the mutant TyrR(V67A), TyrR(Y72C), TyrR(E201G), and TyrR(V67A Y72C E201G) proteins were examined in vivo. Interestingly, as opposed to the wild-type TyrR protein, the mutant TyrR(V67A) protein had a repressive effect on the tyrP promoter in the presence of phenylalanine as the coeffector.

[Bacterial L-asparaginase and glutamin(asparagin)ase: some properties, structure and anti-tumor activity]

Experimental material on structurally and functional organization, regulation of biosynthesis and activity, mechanism of action, genetic determinants, heterologous expression of bacterial L-asparaginases is accumulated. The modern approaches to isolation and purification of these enzymes, some questions of practical using in oncology in the schedules combined chemotherapy of leukemia the native and modified forms of L-asparaginases are discussed. The some results before carried out in the IBMC RAMS and number institutes of the Russia on study bacterial L-asparaginases and glutamine(asparagine)ases are summarized.

Characterization and properties of intracellular proteins after cold acclimation of the ice-nucleating bacterium Pantoea agglomerans (Erwinia herbicola) IFO12686

The ice-nucleating bacterium Pantoea agglomerans (Erwinia herbicola) IFO12686 (INA(+)) responds to a decrease in temperature by the induction of proteins. The pattern of protein bands from strain IFO12686 following a shift in temperature from 30 to 12 degrees C could be divided into four major groups: (1) increasing protein bands, (2) decreasing protein bands, (3) increasing--decreasing protein bands, and (4) almost constant protein bands. We identified a cryoprotective function in the increasing protein band found in strain IFO12686. The increasing protein bands that followed a reduction in temperature were considered to have an important role in cold acclimation or adaptation. We showed that these proteins possessed cryoprotective activity when tested against the freeze-labile enzyme lactate dehydrogenase. The strain IFO12686 had greater cryotolerance than Pa. agglomerans IAM1595 (INA(-)), and the degree of cryotolerance was increased by cold acclimation.

[Studies on gene knocking out of 2-keto aldose reductases from Erwinia sp. SCB125]

Based on the reported gene sequences, the segments containing 2-keto aldose reductase (2-KRA and B) genes were amplified by PCR from the plasmids and Erwinia sp. SCB125 each for gene expression and gene knocking out. Then cloning them into expression vector pBL and successfully expressing them with high enzyme activity in E. coli DH5 alpha. After their enzyme activities were proved, the work on gene knock out followed. Introducing the knock-out vector which distribute unstably during the cell division to the host strains Erwinia sp. SCB125. Screening firstly by the positive marker, one resistance which resulted from the expression of the resistance gene inserting inside the reductase genes and the negative marker, another resistance which outside the reductase genes in the vector. The strains selected out will be tested by further study. This work was the bases of blocking the pathway metabolism and constructing a recombinant strain that can produce 2-KLG directly from D-glucose by one-step fermentation.

[Optimization of culture media and conditions for cultivating Erwinia sp., a producer of fumarase and aspartase]

Mathematical methods of experimental design were used to determine the optimal concentrations of nutrient medium components, aeration conditions, and pH providing for the maximum biomass yields, as well as fumarase and aspartase activities, during submerged cultivation of Erwinia sp. The data showed that different concentrations of carbon source (molasses) and pH of the nutrient medium were required to reach the maximum yields of fumarase and aspartase. Calculations suggested that the combination of these optimized factors would result in 3.2-, 3.4-, and 3.8-fold increases in the Erwinia sp. biomass, aspartase activity, and fumarase activity yields, respectively. The experimental data were consistent with these estimates to a 80% accuracy.

Structure and function of pectic enzymes: virulence factors of plant pathogens

The structure and function of Erwinia chrysanthemi pectate lysase C, a plant virulence factor, is reviewed to illustrate one mechanism of pathogenesis at the molecular level. Current investigative topics are discussed in this paper.

Members of the amylovora group of Erwinia are cellulolytic and possess genes homologous to the type II secretion pathway

A cellulase-producing clone was isolated from a genomic library of the Erwinia rhapontici (Millard) Burkholder strain NCPPB2989. The corresponding gene, named celA, encodes an endoglucanase (EC 3.2.1.4) with the extremely low pH optimum of 3.4 and a temperature optimum between 40 and 50 degrees C. A single ORF of 999 nt was found to be responsible for the Cel activity. The corresponding protein, named CelA, showed 67% identity to the endoglucanase Y of E. chrysanthemi and 51.5% identity to the endoglucanase of Cellulomonas uda, and thus belongs to the glycosyl hydrolase family 8. The celA gene, or its homologue, was found to be present in all E. rhapontici isolates analysed, in E. chrysanthemi, and in E. amylovora. The presence of plant cell wall-degrading enzymes in the amylovora group of Erwinia spp. had not previously been established. Furthermore, the DNA of both E. rhapontici and E. amylovora was found to exhibit homology to genes encoding the type II (GSP) secretion pathway, which is known to be responsible for extracellular targeting of cellulases and pectinases in Erwinia spp. that cause soft rotting, such as E. carotovora and E. chrysanthemi. Secretion of the CelA protein by E. rhapontici could not be verified. However, the CelA protein itself was found to include the information necessary for heterologous secretion by E. chrysanthemi.

False fertilization in sea urchin eggs induced by diabolin, a 120K kelp protein

A 120K lectin-like protein was isolated from the kelp Laminaria diabolica (Oni-kombu), with a unique activity to induce false fertilization specifically in the eggs of the sea urchin Hemicentrotus pulcherrimus. The protein designated as "diabolin" rendered the unfertilized egg forms and elevated the fertilization envelope without insemination at 18 nM half-maximally. Those eggs with elevated fertilization envelopes, however, could not enter into normal cleavage or further development, and hence the proliferation of the sea urchin was hindered. Diabolin, thus, by its unique defense mechanism protects the kelp from the predator sea urchin. It was partially sequenced and found to have the highest homology with phytoene dehydrogenase from the plant virus Erwinia uredovora. A question was left to be solved as to how the kelp on the southeast coast of Hokkaido Island could develop the defense mechanism against the sea urchin on Honshu Island separated by Tsugaru Straits.

ELISA to evaluate plasma anti-asparaginase IgG concentrations in patients with acute lymphoblastic leukemia

The development of antibodies to asparaginase may attenuate the pharmacologic effect of asparaginase treatment, may be associated with hypersensitivity reactions, and may necessitate switching to a different commercial asparaginase preparation for current or future therapy. Thus, development of an ELISA for measurement of anti-asparaginase antibody levels is important in the clinical setting. An anti-asparaginase antibody reference was established by screening 65 plasma samples from six patients with acute lymphoblastic leukemia (ALL) who had recently developed a hypersensitivity reaction to Escherichia coli or Erwinia chrysanthemi asparaginase therapy. Twenty-one plasma samples were selected for the anti-asparaginase antibody reference pool. Five micrograms per milliliter of commercial E. coli and Erwinia asparaginase and 10 microg/ml of E. coli asparaginase conjugated with polyethylene glycol (PEG asparaginase) were found to be optimal as coating antigen concentrations. Anti-asparaginase antibody concentrations were determined using a commercial polyclonal goat anti-human IgG horseradish peroxidase conjugate. The antibody reference curves were linear in a range of absorbance from 0.1 to 1. 5 O.D. units for dilutions from 1:1600 to 1:51,200. Inter-assay coefficients of variation were 9.04, 14.7 and 13.0%, and intra-assay coefficients of variation were 1.44, 4.43 and 3.28% for antibodies against E. coli, Erwinia, and PEG L-asparaginase, respectively. The cut-off for positivity in plasma was determined as mean+2 S.D. of the optical density values for plasma from untreated healthy volunteers. Measurement of specific IgG by this ELISA allows for the evaluation of plasma anti-asparaginase antibody concentrations in patients receiving one or more of the multiple commercial L-asparaginase preparations.

Performance of selected microbial pectinases on synthetic monomethyl-esterified di- and trigalacturonates

Two monomethyl esters of alpha-(1-4)-linked D-galacturonic dimers and three monomethyl esters of alpha-(1-4)-linked D-galacturonic acid trimers were synthesized chemically and further used as substrates in order to establish the substrate specificity of six different endopolygalacturonases from Aspergillus niger, one exopolygalacturonase from Aspergillus tubingensis, and four selected Erwinia chrysanthemi pectinases; exopolygalacturonan hydrolase X (PehX), exopolygalacturonate lyase X (PelX), exopectate lyase W (PelW), and oligogalacturonan lyase (Ogl). All A. niger endopolygalacturonases (PGs) were unable to hydrolyze the two monomethyldigalacturonates and 2-methyltrigalacturonate, whereas 1-methyltrigalacturonate was only cleaved by PGI, PGII, and PGB albeit at an extremely low rate. The hydrolysis of 3-methyltrigalacturonate into 2-methyldigalacturonate and galacturonate by all endopolygalacturonases demonstrates that these enzymes can accommodate a methylgalacturonate at subsite -2. The A. tubingensis exopolygalacturonase hydrolyzed the monomethyl-esterified digalacturonates and trigalacturonates although at lower rates than for the corresponding oligogalacturonates. 1-Methyltrigalacturonate was hydrolyzed at the same rate as trigalacturonate which demonstrates that the presence of a methyl ester at the third galacturonic acid from the nonreducing end does not have any effect on the performance of exopolygalacturonase. Of the four E. chrysanthemi pectinases, Ogl was the only enzyme able to cleave digalacturonate, whereas all four enzymes cleaved trigalacturonate. Ogl does not cleave monomethyl-esterified digalacturonate and trigalacturonate in case the second galacturonic acid residue from the reducing end is methyl-esterified. PehX did not hydrolyze any of the monomethyl-esterified trigalacturonates. The two lyases, PelX and PelW, were both only able to cleave 1-methyltrigalacturonate into Delta4,5-unsaturated 1-methyldigalacturonate and galacturonate.

Transcriptional regulation of tyrosine phenol-lyase gene mediated through TyrR and cAMP receptor protein

Using a lac reporter system in Escherichia coli, we showed that the expression of E. herbicola tpl was regulated through TyrR and cAMP receptor protein. Three TyrR boxes upstream of tpl were essential for full expression. The results suggested that the tyrosine-mediated TyrR hexamerization was an important process. The DNA bending between two TyrR boxes, which is triggered by the binding of cAMP receptor protein, may facilitate the conformational change of TyrRs.

The three asparaginases. Comparative pharmacology and optimal use in childhood leukemia

Asparaginase (ASP) is a standard component of the antileukemia armamentarium. There are currently 3 preparations of asparaginase available: (1) E. coli (ASP, Elspar); (2) the enzyme derived from Erwinia chrysanthemi (ERW, Erwinase); (3) pegaspargase (PEG, Oncaspar), the E. coli enzyme modified by covalent attachment of polyethylene glycol. This report describes the findings of 3 pharmacologic end points: ASP enzyme activity in patients' sera, depletion of asparagine and the development of anti-ASP antibodies. Pharmacokinetics and pharmacodynamic studies in a group of naive children with newly diagnosed ALL demonstrate a significant difference in apparent half-life (1.24 days E. coli vs. 0.65 ERW vs. 5.73 PEG; p < 0.001) and days of asparagine depletion (14-23 E. coli vs. 7-15 ERW vs. 26-34 PEG; p < 0.01) for the 3 different preparations. Data from Pediatric Oncology Group (POG) Protocol #8866 show that high antibody levels correlated with rapid ASP clearance and a significantly lower response rate (NR = 26% vs. CR + PR + 64%). The pharmacologic characteristics of ASP in terms of clearance of enzyme activity and ability to deplete serum asparagine was dependent upon the nature of the enzyme and are significantly altered in patients who develop anti-ASP antibodies regardless of their clinical status. In addition, these data demonstrate that ASP pharmacokinetics are directly related to its anti-leukemic effect. In order to maximize the therapeutic benefits of ASP, the optimal dose and schedule of treatment should be determined based on pharmacologic testing rather than by clinical criteria alone. Future studies will focus on the role of "silent hypersensitivity" as a mechanism of resistance to ASP and strategies to maximize the therapeutic efficacy of ASP as part of ALL therapy.

Effect of glucocorticoids, E. coli- and Erwinia L-asparaginase on hemostatic proteins in children with acute lymphoblastic leukemia

BACKGROUND

The concentrations of plasma hemostatic proteins were analyzed prospectively in 42 children with acute lymphoblastic leukemia (ALL), treated according to the protocol ALL-BFM-90.

PROCEDURE

Treatment included glucocorticosteroids (GC), E. coli L-asparaginase (Asparaginase, Medac) or Erwinia L-asparaginase (Erwinase, Speywood), vincristine, anthracyclines and intrathecal methotrexate. The analysis of hemostatic proteins was performed during induction and re-induction therapy.

RESULTS

At diagnosis, the plasma concentrations of fibrinogen, antithrombin III (AT), plasminogen and protein C were within normal limits, whereas the von Willebrand factor antigen (vWF:Ag) was elevated. After eight days of mono-therapy with GC the concentration of fibrinogen decreased to 59%, vWF:Ag decreased to 67%, AT increased to 124%, protein C increased to 201% of the initial value (mean all p < or = 0.01), while the concentration of plasminogen remained unchanged. During the re-induction phase, the concentrations of the hemostatic proteins, with exception of vWF:Ag, altered in a similar way in response to GC as observed during the induction phase. Administration of two doses of E. coli L-asparaginase (10,000 U/m2) during the induction therapy led to a significant decrease of AT (123 +/- 24 to 63 +/- 15%/mL), protein C (168 +/- 34 to 87 +/- 19%/mL), plasminogen (94 +/- 21 to 41 +/- 12%/mL) and fibrinogen (148 +/- 59 to 79 +/- 30 mg/dL, p < or = 0.01 for all parameters). In contrast, administration of two doses of Erwinia L-asparaginase (10,000 U/m2) during re-induction therapy did not lead to change in the concentration of AT, protein C or plasminogen, and the decrease in fibrinogen (162 +/- 17 to 121 +/- 24 mg/dL) was less pronounced.

CONCLUSIONS

Our results indicate that GC and E. coli L-asparaginase, in particular, induce hemostatic alterations which have implications on our understanding of thrombotic and hemorrhagic events during the treatment of ALL in children.

Molecular characterization of a protease secreted by Erwinia amylovora

A protease with a molecular mass of 48 kDa is secreted by the fire blight pathogen Erwinia amylovora in minimal medium. We characterized this activity as a metalloprotease, since the enzyme was inhibited by EDTA and o -phenanthroline. A gene cluster was determined to encode four genes connected to protease expression, including a structural gene (prtA) and three genes (prtD, prtE, prtF) for secretion of the protease, which are transcribed in the same direction. The organization of the protease gene cluster in E. amylovora is different from that in other Gram-negative bacteria, such as Erwinia chrysanthemi, Pseudomonas aeruginosa and Serratia marcescens. On the basis of the conservative motif of metalloproteases, PrtA was identified to be a member of the metzincin subfamily of zinc-binding metalloproteases, and was confirmed to be the 48 kDa protease on gels by sequencing of tryptic peptide fragments derived from the protein. The protease is apparently secreted into the external medium through the type I secretion pathway via PrtD, PrtE and PrtF which share more than 90% identity with the secretion apparatus for lipase of S. marcescens. A protease mutant was created by Tn 5 -insertions, and the mutation localized in the prtD gene. The lack of protease reduced colonization of an E. amylovora secretion mutant labelled with the gene for the green fluorescent protein (gfp) in the parenchyma of apple leaves.

Enzyme-based flow injection analysis system for glutamine and glutamate in mammalian cell culture media

We present the setup of a flow injection analysis system designed for on-line monitoring of glutamate and glutamine. These amino acids represent a major energy source in mammalian cell culture. A cycling assay consisting of glutamate dehydrogenase and aspartate aminotransferase produces NADH proportional to the glutamate concentration in the sample. NADH is then measured spectrophotometrically. Glutamine is determined by conversion to glutamate which is fed into the cycling assay. The conversion of glutamine to glutamate is catalyzed by asparaginase. Asparaginase was used in place of glutaminase due to its relatively high reactivity with glutamine and a pH optimum similar to that of glutamate dehydrogenase. The enzymes were immobilized covalently to activated controlled pore glass beads and integrated into the flow injection analysis system. The application of the immobilized enzymes and the technical setup are presented in this paper.

Pharmacokinetic dose adjustment of Erwinia asparaginase in protocol II of the paediatric ALL/NHL-BFM treatment protocols

Native forms of asparaginase stem from different biological sources. Previously reported data from children treated with Erwinase showed significantly lower trough levels and pharmacokinetic dose intensity than after E. coli-derived preparations. Hence, schedule optimization was initiated to achieve relevant serum activities. 21 children on reinduction therapy received Erwinase on Mondays, Wednesdays and Fridays for 3 weeks (9 x 20000 IU/m2 i.v.) instead of 4x 10 000IU/m2 of E. coli asparaginase (twice weekly for 2 weeks). Asparaginase trough activities were measured as the primary parameter, targeting 100-200 IU/I after 2 d and >50 IU/l after 3 d. Concurrently, asparagine trough concentrations were monitored. The mean trough activity was 156+/-99 IU/l, with 2/108 samples showing no detectable activity. Regarding trough levels per individual (three or more measurements/patient), means ranged from 52+/-29 to 276+/-114 IU/l (20 patients, 106 samples), with nine, six, and five children inside, below, and above the target range, respectively. The mean 3 d trough activity was 50+/-39 IU/l (20 patients, 51 samples). In 11 of these samples no activity was measurable. Mean trough activities calculated per individual ranged from < 20-84+/-30 IU/l (14 patients, 42 samples) with seven children below the target limit of 50 IU/l and asparagine concentrations <0.2 - 1.5microM. We concluded that an increased dose of 9x20000 IU/m2 of Erwinia asparaginase within 3 weeks resulted in a pharmacokinetic dose intensity comparable to former observations made with 4 x 10 000IU/m2 of the E. coli product Crasnitin which is no longer marketed. High interindividual variability and the phenomenon of 'silent' inactivation necessitate monitoring wherever possible.

Two Arabidopsis thaliana carotene desaturases, phytoene desaturase and zeta-carotene desaturase, expressed in Escherichia coli, catalyze a poly-cis pathway to yield pro-lycopene

We have expressed in Escerichia coli the enzymes geranylgeranyl diphosphate synthase and phytoene synthase, from the soil bacterium Erwinia stewartii, and the two carotene desaturases phytoene desaturase and carotene zeta-carotene desaturase from Arabidopsis thaliana. We show that pro-lycopene (7,9,7',9'-tetra-cis)-lycopene is the main end product of the plant desaturation pathway in these cells. In addition, light is required in this system. Whereas in the dark mainly zeta-carotene, the phytoene desaturase product, accumulates, illumination leads to activation of this intermediate caused by its photoisomerization. zeta-Carotene then meets the stereospecific requirements of zeta-carotene desaturase and pro-lycopene is formed. In contrast, a strain of E. coli carrying geranylgeranyl diphosphate synthase, phytoene desaturase and the bacterial carotene desaturase CrtI, which mediates lycopene formation from phytoene, does not require light, nor is a poly-cis-lycopene species formed. The stereoselectivity of the plant-type desaturation pathway expressed in E. coli is the same as previously shown with chromoplast membranes. As the phytoene desaturase and zeta-carotene desaturase used originate from a system not capable of developing chromoplasts, this indicates that the poly-cis pathway of carotene desaturation may have a wider occurrence than initially believed.