Structural and rheological properties of diluted alkali soluble pectin from apple and carrot

Pectin, a complex polysaccharide found in plant cell walls, plays a crucial role in various industries due to its functional properties. The diluted alkali-soluble pectin (DASP) fractions that result from the stepwise extraction of apples and carrots were studied to evaluate their structural and rheological properties. Homogalacturonan and rhamnogalacturonan I, in different proportions, were the main pectin domains that composed DASP from both materials. Atomic force microscopy revealed that the molecules of apple DASP were longer and more branched. A persistence length greater than 40 nm indicated that the pectin molecules deposited on mica behaved as stiff molecules. The weight-averaged molar mass was similar for both samples. Intrinsic viscosity values of 194.91 mL·g-1 and 186.79 mL·g-1 were obtained for apple and carrot DASP, respectively. Rheological measurements showed greater structural strength for apple-extracted pectin, whereas carrot pectin was characterized by a higher linear viscoelasticity limit. This comparison showed that the pectin fractions extracted by diluted alkali are structurally different and have different rheological properties depending on their botanical origin. The acquired insights can enhance the customized use of pectin residue and support further investigations in industries relying on pectin applications.

A study of the properties of hemicelluloses adsorbed onto microfibrillar cellulose isolated from apple parenchyma

Binding assays of commercially available hemicelluloses and pectins, and microfibrillar cellulose isolated form apple parenchyma were prepared. Initial studies showed that among all of the non-cellulosic polysaccharides examined, only the hemicelluloses (xyloglucan, xylan, glucomannan, ß-d-glucan) showed the ability to adsorb to microfibrillar cellulose. Among several adsorption models tested, the best fit was obtained for the Redlich-Peterson isotherm. Moreover, the linear vs. the branched structure and the size of the hemicelluloses have an influence over the extent of the adsorption to cellulose. The Fourier Transform Infrared and Raman spectra showed that a rather weak interaction took place between the hemicelluloses and cellulose. Also, the differential scanning calorimetry and the light scattering method results showed that after adsorption, cellulose has less mobility. Moreover, the mechanical properties of cellulose films changed after the addition of the chosen hemicelluloses and the films became less elastic but more resistant to a breaking force.

Influence of pectin and hemicelluloses on physical properties of bacterial cellulose

The properties of bacterial cellulose (BC)-based films produced by in situ biosynthesis with various polysaccharides (water-soluble pectin, arabinan, rhamnogalacturonan I, arabinoxylan, xyloglucan, glucomannan) were investigated. The addition of the polysaccharides to the bacterial growth environment changed the composition of the films by incorporating characteristic monosaccharides. BC-based films contained up to 26.7 % of non-cellulosic polysaccharides. The applied modification had a clear impact on water sorption and caused a decrease in the thermal stability of most BC films, which was connected with the depletion of geometrical dimensions of cellulose nanofibers observed with AFM. The FT-IR and Raman spectra demonstrated a decrease in % Iα of cellulose films, most notably for xyloglucan and glucomannan, as well as a change in their degree of crystallinity and the length of cellulose chains. The addition of xyloglucan had the most pronounced effect on film hardening; the other additives had a similar but lesser effect.

The Influence of High-Intensity Ultrasonication on Properties of Cellulose Produced from the Hop Stems, the Byproduct of the Hop Cones Production

The goal of this work is to evaluate the hop stems, a byproduct of hop cones production, as a potential source of cellulose. Hop stems contain up to 29% of cellulose. The cellulose isolation was conducted through the thermochemical treatment. After high-speed blending, the cellulose was characterized by 67% of crystallinity degree obtained from X-ray diffraction and median diameter of 6.7 nm obtained from atomic force microscopy imaging. The high-intensity ultrasonication (HIUS) was applied to reach further disintegration of cellulose fibers. The longer HIUS treatment resulted in decrease in crystallinity degree even up to 60% and decrease in the fiber diameter up to 4 nm. The Fourier transform infrared spectroscopy (FTIR) spectra showed that HIUS treatment led to changes in intermolecular hydrogen bonds. The stability of cellulose dispersions versus length of HIUS treatment was monitored over 14 days with back dynamic light scattering and laser Doppler electrophoresis methods. Obtained results are evidence that the hop stems are a potential source of cellulose and that it is possible to obtain stable dispersions after HIUS treatment. This was the first time that the properties of hop cellulose have been described so extensively and in detail after the use of HIUS treatment.

Structural properties of diluted alkali-soluble pectin from Pyrus communis L. in water and salt solutions

The self-assembly and gelation of low-methoxyl diluted alkali-soluble pectin (LM DASP) from pear fruit (Pyrus communis L. cv. Conference) was studied in water and salt solutions (NaCl and CaCl₂, constant ionic strength) without pH adjustment at 20 °C. The samples at different LM DASP concentrations were characterized using rheological tests, Fourier-transform infrared spectroscopy, dual-angle dynamic light scattering and atomic force microscopy. LM DASP from pear fruit (Pyrus communis L.) showed gelling ability. The indices (aggregation index and shape factor) based on light scattering may be useful for the characterization of structural changes in polysaccharide suspension, particularly for the determination of a gel point. The results obtained may be important for the food, cosmetic and pharmaceutical industries where pectin is used as a texturizer, an encapsulating agent, a carrier of bioactive substances or a gelling agent.

Aggregation and weak gel formation by pectic polysaccharide homogalacturonan

This study presents a novel model of homogalacturonan (HG) based on the dissipative particle dynamics (DPD). The model was applied to investigate the mechanism of self-aggregation of low-methoxylated homogalacturonan in aqueous solutions in the absence of cations. The coarse-grained model provided new insights into the structural features of HG aggregates and networks in aqueous solutions. Depending on the properties and concentration of polysaccharides, two major patterns of self-assembly were observed for HG - ellipsoidal aggregates and a continuous three-dimensional network. Simulations showed that a decrease in the degree of dissociation of HG results in a higher rate of self-aggregation, as well as facilitating the formation of larger assemblies or thicker nanofilaments depending on the type of final self-assembly. Simulations of polysaccharides of different chain lengths suggested the existence of a structural threshold for the formation of a spatial network for HG consisting of less than 35 GalA units.

Effect of different conditions of synthesis on properties of silver nanoparticles stabilized by nanocellulose from carrot pomace

The silver nanoparticles (AgNPs) can exhibit different optical properties depending on their size and shape as a result of synthesis method and the stabilizer used. In this research the synthesis of AgNPs in the presence of nanocellulose obtained from carrot pomace was investigated. The influence of silver nitrate concentration, temperature and mechanical agitation on size and shape of AgNPs was studied. The mixing of reagents during synthesis, regardless temperature, led to obtain AgNPs of various sizes and shapes. It was confirmed by different colors of samples with absorbance maximum from 334 to 779 nm, the transmission electron microscopy images and dynamic light scattering results. In unmixed samples only spherical nanoparticles with absorbance maximum at 408 nm were observed. Obtained results have demonstrated that mechanical agitation and an appropriate silver nitrate concentration combined with stabilizing effect of nanocellulose allow to obtain AgNPs in different shapes and sizes.

The Effect of Concentration on the Cross-Linking and Gelling of Sodium Carbonate-Soluble Apple Pectins

The cross-linking and gelation of low-methoxy pectins are basic processes commonly used in different industries. The aim of this research was to evaluate the cross-linking process of the sodium carbonate-soluble pectins (named DASP) extracted from apples, characterized by a low degree of methylesterification as a function of its concentration in water (CDASP). The cross-linking process was studied with a dynamic light scattering method, atomic force microscope (AFM), viscosity and pH measurements. An increase in CDASP above 0.01% resulted in a decrease in the aggregation index (AI) and the change of its sign from positive to negative. The value of AI = 0 occurred at CDASP = 0.33 ± 0.04% and indicated the formation of a pectin network. An increase in CDASP caused the changes in viscosity of pectin solutions and the nanostructure of pectins spin-coated on mica observed with AFM, which confirmed results obtained. The hydrogen bonds were involved in the cross-linking process.

Extracellular polysaccharide protects Rhizobium leguminosarum cells against zinc stress in vitro and during symbiosis with clover

Rhizobium leguminosarum bv. trifolii is a soil bacterium that establishes symbiosis with clover (Trifolium spp.) under nitrogen-limited conditions. This microorganism produces exopolysaccharide (EPS), which plays an important role in symbiotic interactions with the host plant. The aim of the current study was to establish the role of EPS in the response of R. leguminosarum bv. trifolii cells, free-living and during symbiosis, to zinc stress. We show that EPS-deficient mutants were more sensitive to Zn²⁺ exposure than EPS-producing strains, and that EPS overexpression conferred some protection onto the strains beyond that observed in the wild type. Exposure of the bacteria to Zn²⁺ ions stimulated EPS and biofilm production, and increased cell hydrophobicity. However, zinc stress negatively affected the motility and attachment of bacteria to clover roots, as well as the symbiosis with the host plant. In the presence of Zn²⁺ ions, cell viability, root attachment, biofilm formation and symbiotic efficiency of EPS-overproducing strains were significantly higher than those of the EPS-deficient mutants. We conclude that EPS plays an important role in the adaptation of rhizobia to zinc stress, in both the free-living stage and during symbiosis.

An Interaction of Rhamnolipids with Cu2+ Ions

This study was focused on the description of interaction between Cu²⁺ ions and the 1:1 mono- and dirhamnolipid mixtures in the premicellar and aggregated state in water and 20 mM KCl solution at pH 5.5 and 6.0. The critical micelle concentration of biosurfactants was determined conductometrically and by the pH measurements. Hydrodynamic diameter and electrophoretic mobility were determined in micellar solutions using dynamic light scattering and laser Doppler electrophoresis, respectively. The copper immobilization by rhamnolipids, methylglycinediacetic acid (MGDA), and ethylenediaminetetraacetic acid (EDTA) was estimated potentiometrically for the Cu²⁺ to chelating agent molar ratio from 16:100 to 200:100. The degree of ion binding and the complex stability constant were calculated at a 1:1 metal to chelant molar ratio. The aggregates of rhamnolipids (diameter of 43-89 nm) were negatively charged. Biosurfactants revealed the best chelating activities in premicellar solutions. For all chelants studied the degree of metal binding decreased with the increasing concentration of the systems. The presence of K⁺ lowered Cu²⁺ binding by rhamnolipids, but did not modify the complex stability significantly. Immobilization of Cu²⁺ by biosurfactants did not cause such an increase of acidification as that observed in MGDA and EDTA solutions. Rhamnolipids, even in the aggregated form, can be an alternative for the classic chelating agents.

Surface properties of Enterococcus faecalis cells isolated from chicken hearts determine their low ability to form biofilms

Enterococcus faecalis is one of the most significant bacterial pathogens associated with the first-week mortality of chickens. Here, the surface properties of bacterial cells and the selected virulence factors of E. faecalis strains isolated from the hearts of clinically healthy broiler chickens were studied. Investigations were carried out on live and autoclaved cells. E. faecalis (ATCC 29212) was used as a reference strain. The bacterial cells revealed different haemolytic activities. Their surface free energy was dominated by the hydrophobic component. The cell walls of the bird isolates showed slightly weaker acidic characteristics than those of E. faecalis (ATCC 29212). Moreover, the bacterial cells from the chicken hearts showed higher electrophoretic mobility and surface electrical charge than the reference strain, and consequently demonstrated a low ability to form biofilms.

Studies on the removal of Cd ions by gastrointestinal lactobacilli

Accumulation of toxic metal ions in food and water is nowadays a growing health-related problem. One detoxification method involves the use of microorganisms naturally inhabiting the gastrointestinal tract (GIT). The purpose of this study was to prove that lactic acid bacteria derived from the GIT are able to effectively remove Cd²⁺ from water solution. Seven strains of lactobacilli, out of 11 examined, showed tolerance to high concentrations of cadmium ions. The metal-removal efficiencies of these seven lactobacilli ranged from 6 to 138.4 μg/h mg. Among these bacteria, Lactobacillus gallinarum and Lactobacillus crispatus belonged to the highest (85%) Cd-removal efficiency class. An analysis of the zeta potential (ζ) indicated that the bacterial cell surface had a negative charge at the pH ranging from 3 to 10. The presence of carboxyl, amide, and phosphate groups was favorable for Cd²⁺ binding to the cell surface, which found confirmation in FTIR-ATR spectra. Elemental SEM/EDS analysis and TEM imaging not only confirmed the adsorption of Cd²⁺ on the cell envelope but also gave us a reason to suppose that Lb. crispatus accumulates metal ions inside the cell. Our findings open perspectives for further research on the new biological function of GIT lactobacilli as natural biosorbents.

A QM-MD simulation approach to the analysis of FRET processes in (bio)molecular systems. A case study: complexes of E. coli purine nucleoside phosphorylase and its mutants with formycin A

Predicting FRET pathways in proteins using computer simulation techniques is very important for reliable interpretation of experimental data. A novel and relatively simple methodology has been developed and applied to purine nucleoside phosphorylase (PNP) complexed with a fluorescent ligand — formycin A (FA). FRET occurs between an excited Tyr residue (D*) and FA (A). This study aims to interpret experimental data that, among others, suggests the absence of FRET for the PNPF159A mutant in complex with FA, based on novel theoretical methodology. MD simulations for the protein molecule containing D*, and complexed with A, are carried out. Interactions of D* with its molecular environment are accounted by including changes of the ESP charges in S₁, compared to S₀, and computed at the SCF-CI level. FRET probability W_F depends on the inverse six-power of the D*-A distance, R_da. The orientational factor 0 < k² < 4 between D* and A is computed and included in the analysis. Finally W_F is time-averaged over the MD trajectories resulting in its mean value. The red-shift of the tyrosinate anion emission and thus lack of spectral overlap integral and thermal energy dissipation are the reasons for the FRET absence in the studied mutants at pH 7 and above. The presence of the tyrosinate anion results in a competitive energy dissipation channel and red-shifted emission, thus in consequence in the absence of FRET. These studies also indicate an important role of the phenyl ring of Phe159 for FRET in the wild-type PNP, which does not exist in the Ala159 mutant, and for the effective association of PNP with FA. In a more general context, our observations point out very interesting and biologically important properties of the tyrosine residue in its excited state, which may undergo spontaneous deprotonation in the biomolecular systems, resulting further in unexpected physical and/or biological phenomena. Until now, this observation has not been widely discussed in the literature.

Developmental arrest in Caenorhabditis elegans dauer larvae causes high expression of enzymes involved in thymidylate biosynthesis, similar to that found in Trichinella muscle larvae

Crude extract specific activities of thymidylate synthase, dUTPase, thymidine kinase and dihydrofolate reductase were high during the development of Caenorhabditis elegans, the dauer larva activities being similar to those previously determined in Trichinella spiralis and T. pseudospiralis muscle larvae (with the exception of thymidine kinase, not detected in Trichinella). High thymidylate synthase expression in developmentally arrested larvae, demonstrated also at the mRNA and protein levels, is in agreement with a global cell cycle arrest of dauer larvae and indicates this unusual cell cycle regulation pattern can be shared by developmentally arrested larvae of C. elegans and the two Trichnella species. Hence, the phenomenon may be characteristic for developmentally arrested larvae of different nematodes, rather than specific for the parasitic Trichinella muscle larvae. Endogenous C. elegans thymidylate synthase was purified and its molecular properties compared with those of the recombinant protein, expression of the latter in E. coli cells confirming the NCBI database sequence identity.

Trichinella spiralis thymidylate synthase: cDNA cloning and sequencing, and developmental pattern of mRNA expression

The persistent expression of thymidylate synthase activity has previously been demonstrated not only in adult forms, but also in non-developing muscle larvae of Trichinella spiralis and T. pseudospiralis, pointing to an unusual pattern of cell cycle regulation, and prompting further studies on the developmental pattern of T. spiralis thymidylate synthase gene expression. The enzyme cDNA was cloned and sequenced, allowing the characterization of a single open reading frame of 307 amino acids coding for a putative protein of 35,582 Da molecular weight. The amino acid sequence of the parasite enzyme was analysed, the consensus phylogenetic tree built and its stability assessed. The aa sequence identity with thymidylate synthase was confirmed by the enzymatic activity of the recombinant protein expressed in E. coli. As compared with the enzyme purified from muscle larvae, it showed apparently similar Vmax value, but higher Km(app) values desscribing interactions with dUMP (28.8 microM vs. 3.9 microM) and (6RS,alphaS)-N(5,10)-methylenetetrahydrofolate (383 microM vs. 54.7 microM). With the coding region used as a probe, thymidylate synthase mRNA levels, relative to 18S rRNA, were found to be similar in muscle larvae, adult forms and newborn larvae, in agreement with muscle larvae cells being arrested in the cell cycle.

Peripheral blood lymphocyte population in children infected with Helicobacter pylori

PURPOSE

Helicobacter pylori infection in children is associated with a chronic inflammatory process of gastric and duodenal mucosa, which may have a various clinical course ranging from asymptomatic and chronic inflammatory condition to gastric ulceration. The immune system may contribute especially to chronic gastric mucosa inflammation. The aim of our study was to assess the levels of peripheral blood T (CD3+, CD4+, CD8+) and B lymphocyte subpopulation (CD19+) in children with Helicobacter pylori infection and to evaluate their relation to degree of antrum mucosa inflammation.

MATERIAL AND METHODS

The study was performed in 32 children aged 7-18 years, hospitalized due to dyspeptic symptoms. The endoscopic examination of upper gastrointestinal tract was performed and gastric and duodenal mucosa was estimated in all patients. The endoscopic and histological evaluation of gastric mucosa was performed according to the Sydney System [4]. The urease test (CLO-test-H. pylori) was made to estimate the severity of the infection.

RESULTS

Moderate antrum mucosa inflammation was found in 41.2% of the examined. The highest percentage of children (58.8%) presented marked inflammation. No mild inflammation was found in children examined.

CONCLUSIONS

No correlation was found between lymphocyte levels and the degree of the inflammatory changes in antrum mucosa. The evaluation of peripheral blood lymphocytes performed in children with Helicobacter pylori infection suggests that T lymphocytes may play a predominant role in this infection.

Interaction of thymidylate synthase with the 5'-thiophosphates, 5'-dithiophosphates, 5'-H-phosphonates and 5'-S-thiosulfates of 2'-deoxyuridine, thymidine and 5-fluoro-2'-deoxyuridine

New analogs of dUMP, dTMP and 5-fluoro-dUMP, including the corresponding 5'-thiophosphates (dUMPS, dTMPS and FdUMPS), 5'-dithiophosphates (dUMPS2, dTMPS2 and FdUMPS2), 5'-H-phosphonates (dUMP-H, dTMP-H and FdUMP-H) and 5'-S-thiosulfates (dUSSO3, dTSSO3 and FdUSSO3), have been synthesized and their interactions studied with highly purified mammalian thymidylate synthase. dUMPS and dUMPS2 proved to be good substrates, and dTMPS and dTMPS2 classic competitive inhibitors, only slightly weaker than dTMP. Their 5-fluoro congeners behaved as potent, slow-binding inhibitors. By contrast, the corresponding 5'-H-phosphonates and 5'-S-thiosulfates displayed weak activities, only FdUMP-H and FdUSSO3 exhibiting significant interactions with the enzyme, as weak competitive slow-binding inhibitors versus dUMR The pH-dependence of enzyme time-independent inhibition by FdUMP and FdUMPS was found to correlate with the difference in pKa values of the phosphate and thiophosphate groups, the profile of FdUMPS being shifted (approximately 1 pH unit) toward lower pH values, so that binding of dUMP and its analogs is limited by the phosphate secondary hydroxyl ionization. Hence, together with the effects of 5'-H-phosphonate and 5'-S-thiosulfate substituents, the much weaker interactions of the nucleotide analogs (3-5 orders of magnitude lower than for the parent 5'-phosphates) with the enzyme is further evidence that the enzyme's active center prefers the dianionic phosphate group for optimum binding.

5-Substituted N(4)-hydroxy-2'-deoxycytidines and their 5'-monophosphates: synthesis, conformation, interaction with tumor thymidylate synthase, and in vitro antitumor activity

Convenient procedures are described for the synthesis of 5-substituted N(4)-hydroxy-2'-deoxycytidines 5a,b,d-h via transformation of the respective 5-substituted 3', 5'-di-O-acetyl-2'-deoxyuridines 1a-c,e-h. These procedures involved site-specific triazolation or N-methylimidazolation at position C(4), followed by hydroxylamination and deblocking with MeOH-NH(3). Nucleosides 5a,b,d-h were selectively converted to the corresponding 5'-monophosphates 6a,b,d-h with the aid of the wheat shoot phosphotransferase system. Conformation of each nucleoside in D(2)O solution, deduced from (1)H NMR spectra and confirmed by molecular mechanics calculations, showed the pentose ring to exist predominantly in the conformation S (C-2'-endo) and the N(4)-OH group as the cis rotamer. Cell growth inhibition was studied with two L5178Y murine leukemia cell lines, parental and 5-fluoro-2'-deoxyuridine (FdUrd)-resistant, the latter 70-fold less sensitive toward FdUrd than the former. With FdUrd-resistant L5178Y cells, 5-fluoro-N(4)-hydroxy-2'-deoxycytidine (5e) caused almost 3-fold stronger growth inhibition than FdUrd; 5e was only some 3-fold weaker growth inhibitor of the resistant cells than of the parental cells. Thymidylate synthase inhibition was studied with two forms of the enzyme differing in sensitivities toward 5-fluoro-2'-deoxyuridine 5'-monophosphate (FdUMP), isolated from parental and FdUrd-resistant L1210 cell lines. All N(4)-hydroxy-dCMP (6a,b,d-h) and dUMP analogues studied were competitive vs dUMP inhibitors of the enzyme. Analogues 6b,d-h and 5-hydroxymethyl-dUMP, similar to N(4)-hydroxy-dCMP (6a) and FdUMP, were also N(5), N(10)-methylenetetrahydrofolate-dependent, hence mechanism-based, slow-binding inhibitors. 5-Chloro-dUMP, 5-bromo-dUMP, and 5-iodo-dUMP, similar to dTMP, did not cause a time-dependent inactivation of the enzyme. Instead, they behaved as classic inhibitors of tritium release from [5-(3)H]dUMP. 5-Bromo-dUMP and 5-iodo-dUMP showed substrate activity independent of N(5), N(10)-methylenetetrahydrofolate in the thymidylate synthase-catalyzed dehalogenation reaction. The =N-OH substituent of the pyrimidine C(4) prevented the enzyme-catalyzed release from the C(5) of Br(-) and I(-) (the same shown previously for H(+)). While FdUMP and 6a showed a higher affinity and greater inactivation power with the parental cell than FdUrd-resistant cell enzyme, an opposite relationship could be seen with 5-hydroxymethyl-dUMP.

[Primary forms of extralymphatic non-Hodgkin's lymphoma]

In 1981-1990, 584 patients with non-Hodgkin malignant lymphoma, 209 women and 375 men, aged between 17 and 75 years, were treated at the I Department of Medicine and Department of Hematology, Silesian Medical Academy in Katowice. In this group the primary localization outside lymph nodes was seen in 26 patients (9 women and 17 men), i.e. 4.6% of all patients with malignant non-Hodgkin lymphomas. Most frequently digestive tract was involved-19 patients (73.1%). Twenty three patients were treated surgically followed by chemotherapy and/or irradiation. Not operated patients were treated with either chemotherapy or both radio- and chemotherapy. Complete remission was achieved in 17 patients (65.4%), partial remission in 4 (15.4%) patients. Five patients did not respond to therapy (19.2%). A mean survival time was 49.4, 14.3, and 6.4 months, respectively.

Thymidylate synthases from Hymenolepis diminuta and regenerating rat liver: purification, properties, and inhibition by substrate and cofactor analogues

Comparative studies of thymidylate synthases, isolated from the tapeworm, Hymenolepis diminuta, and regenerating liver of its host, rat, aimed at a possibility of specific inhibition of the helminthic enzyme, are presented. While similar in structure (dimers with monomer molecular masses of 33.7 kDa and 34.9 kDa, respectively) and parameters describing interactions with substrates and products, the tapeworm and rat enzymes differed in the dependences of reaction velocity on temperature (Arrhenius plots biphasic and linear, respectively). The tapeworm, compared with the host, enzyme was less sensitive to the competitive slow-binding inhibition by 5-fluoro-dUMP and its 2-thio congener, but equally sensitive to inhibition by 4-thio-5-fluoro-dUMP, N4-hydroxy-dCMP and N4-hydroxy-5-fluoro-dCMP, the latter being more potent inhibitor of the parasite enzyme than 5-fluoro-dUMP. alpha-Anomer of 5-fluoro-dUMP behaved as a very weak competitive slow-binding inhibitor of both enzymes. Both enzymes differed markedly in sensitivity to inhibition by 10-propargyl-5,8-dideazafolate and its di- and triglutamates (pddPteGlu1-3), with pddPteGlu1 being stronger inhibitor of the mammalian enzyme, but pddPteGlu3 showing opposite specificity. Sulfonamidobenzoylglutamate analogue of pddPteGlu (pddPteSO2Glu) and 2-desamino-2-methyl derivative of this analogue (CH3pddPteSO2Glu) were weaker inhibitors of both enzymes than the parent compound. Substitution of the glutamyl residue in CH3pddPteSO2Glu with either norvaline or alanine increased inhibition potency, whereas similar substitutions with glycine, valine or phenylglycine were without a distinct effect with the host enzyme but weakened inhibition of the tapeworm enzyme.

Promotion of purine nucleotide binding to thymidylate synthase by a potent folate analogue inhibitor, 1843U89

A folate analogue, 1843U89 (U89), with potential as a chemotherapeutic agent due to its potent and specific inhibition of thymidylate synthase (TS; EC 2.1.1.45), greatly enhances not only the binding of 5-fluoro-2'-deoxyuridine 5'-monophosphate (FdUMP) and dUMP to Escherichia coli TS but also that of dGMP, GMP, dIMP, and IMP. Guanine nucleotide binding was first detected by CD analysis, which revealed a unique spectrum for the TS-dGMP-U89 ternary complex. The quantitative binding of dGMP relative to GMP, FdUMP, and dUMP was determined in the presence and absence of U89 by ultrafiltration analysis, which revealed that although the binding of GMP and dGMP could not be detected in the absence of U89 both were bound in its presence. The Kd for dGMP was about the same as that for dUMP and FdUMP, with binding of the latter two nucleotides being increased by two orders of magnitude by U89. An explanation for the binding of dGMP was provided by x-ray diffraction studies that revealed an extensive stacking interaction between the guanine of dGMP and the benzoquinazoline ring of U89 and hydrogen bonds similar to those involved in dUMP binding. In addition, binding energy was provided through a water molecule that formed hydrogen bonds to both N7 of dGMP and the hydroxyl of Tyr-94. Accommodation of the larger dGMP molecule was accomplished through a distortion of the active site and a shift of the deoxyribose moiety to a new position. These rearrangements also enabled the binding of GMP to occur by creating a pocket for the ribose 2' hydroxyl group, overcoming the normal TS discrimination against nucleotides containing the 2' hydroxyl.

Isolation and expression of rat thymidylate synthase cDNA: phylogenetic comparison with human and mouse thymidylate synthases

Two cDNA clones representing rat hepatoma thymidylate synthase (rTS) were isolated from a lambda ZAP II cDNA library using as a probe a fragment of the human TS cDNA. The two were identical except that one was missing 50 bp and the other 23 bp corresponding to the 5' coding region of the protein. The missing region was obtained by screening a rat genomic library. The open reading frame of rTS cDNA encoded 921 bp encompassing a protein of 307 amino acids with a calculated molecular mass of 35,015 Da. Rat hepatoma TS appears identical to normal rat thymus TS and the two sequences differ from mouse TS in the same eight amino acid residues. Six of these differences are in the first 21 amino acids from the amino-end. The human enzyme differed from rat and mouse TS at 17 residues where the latter two were identical, with most changes being conservative in nature. The three species differed completely at only four sites. Because the mouse TS shares four amino acids with human TS at sites which differ from rTS and a comparable situation does not exist between rTS and human TS, it is suggested that mouse TS is closer to human TS phylogenetically than rTS. The polymerase chain reaction was used to subclone the protein coding region of rTS into a high expression vector, which expressed rTS in Escherichia coli to the extent of 10 to 20% of its cellular protein. Although the amino-end of the amplified TS was unblocked, that isolated from a FUdR-resistant rat hepatoma cell line contained mostly N-acetylmethionine on its N-terminal end, a finding that may have significant regulatory consequences, which are discussed. The TS level in the resistant cell line was 60 to 70-fold higher than normal which was found to be associated with both multiple gene copies and an expanded TS mRNA pool.

Interaction of 2-thio-5-fluoro-dUMP and 4-thio-5-fluoro-dUMP with mammalian normal and tumour and helminthic thymidylate synthases: influence of C(4)-substituents on specificity for enzyme inactivation

To determine how 5-fluoro-dUMP modifications may affect its specificity, 2-thio-5-fluoro-dUMP and 4-thio-5-fluoro-dUMP were compared as inhibitors of thymidylate synthases isolated from parental and FdUrd-resistant mouse leukemia L1210 cells, human and rat colon adenocarcinomas, regenerating rat liver and the tapeworm, Hymenolepis diminuta, differing in sensitivity to time- and N5,10-methylenetetrahydrofolate-dependent inactivation by 5-fluoro-dUMP (Ki values ranging from 10(-9) to 10(-7) M). Inactivation by 2-thio-5-fluoro-dUMP, relative to 5-fluoro-dUMP, was 5-20-fold weaker, with specificity for inactivation of different thymidylate synthases paralleling that of 5-fluoro-dUMP. By contrast, 4-thio-5-fluoro-dUMP showed very different specificity, being as potent an inactivator for some enzymes as 5-fluoro-dUMP, but 45-85-fold weaker for others. The results suggest that an interplay between substituents at C(4) and C(5) of the pyrimidine ring may affect the specificity of thymidylate synthase inactivation.

Mechanism of inhibition of mammalian tumor and other thymidylate synthases by N4-hydroxy-dCMP, N4-hydroxy-5-fluoro-dCMP, and related analogues

N4-Hydroxy-dCMP (N4-OH-dCMP), N4-methoxy-dCMP (N4-OMe-dCMP), and their 5-fluoro congeners (syntheses of which are described) were all slow-binding inhibitors of Ehrlich carcinoma thymidylate synthase (TS), competitive with respect to dUMP, and had differing kinetic constants describing interactions with the two TS binding sites. N4-OH-dCMP was not a substrate (no dihydrofolate produced; no tritium released with 5-3H-labeled molecule), and its inactivation of TS was methylenetetrahydrofolate-dependent, hence mechanism-based, with arrest of a step posterior to addition of cofactor and blocking abstraction of the C(5) hydrogen. Ki values for N4-OH-dCMP and its 5-fluoro analogue were in the range 10(-7) - 10(-8) M, 2-3 orders of magnitude higher for the corresponding N4-OMe analogues. The 5-methyl analogue of N4-OH-dCMP was 10(4)-fold less potent, pointing to the anti rotamer of the imino form of exocyclic N4-OH, relative to the ring N(3), as the active species. This is consistent with weaker slow-binding inhibition of the altered enzyme from 5-FdUrd-resistant, relative to parent, L1210 cells by both FdUMP and N4-OH-dCMP, suggesting interaction of both N4-OH and C(5)-F groups with the same region of the active center. Kinetic studies with purified enzyme from five sources, viz., Ehrlich carcinoma, L1210 parental, and 5-FdUrd-resistant cells, regenerating rat liver, and the tapeworm Hymenolepis diminuta, demonstrated that addition of a 5-fluoro substituent to N4-OH-dCMP increased its affinity from 2- to 20-fold for the enzyme from different sources.(ABSTRACT TRUNCATED AT 250 WORDS)

[Results of combined therapy in patients with nonseminomatous testicular tumors]

The results of multidrug therapy of 44 male patients with non-seminomatous testicular tumours are discussed. The diagnosed tumours were of all stages of the clinical advances and were treated with combined chemotherapy (surgery and PVP regimen). Thirty two patients (73%) are followed up between 7 and 103 months and survived, complete remission is noted in 29 patients (66%) including 6 patients who survived over 5 years. Symptoms of the tumour are found in 3 patients. Twelve patients (27%) died. The treatment did not produce life-threatening complications. The obtained results have been compared with those reported by other authors.

Regulation of oxidative decarboxylation of branched-chain 2-oxo acids in rat liver mitochondria

At 0.1 mM 2-oxo[1-14C]isocaproate or 2-oxo[1-14C]isovalerate plots of the reciprocal of the rate of 14CO2 formation by branched-chain 2-oxo acid dehydrogenase complex in mitochondria vs alpha-cyanocinamate concentration were linear up to high inhibitor concentrations, indicating that the monocarboxylate carrier-mediated transport was the rate-limiting step. At low (0.025 mM) concentration of 2-oxo[1-14C]isocaproate or 2-oxo[1-14C]isovalerate the 1/v vs I plots became nonlinear indicating that the branched-chain 2-oxo acid dehydrogenase activity determined the rate of 14CO2 formation. Inhibition of branched-chain 2-oxo acid dehydrogenase complex by clofibric acid or arsenite showed that at 0.1 mM 2-oxoisovalerate the activity of the complex became the rate-limiting step of the pathway. The availability of the 2-oxoisocaproate or 2-oxoisovalerate seems to affect the phosphorylation and the activity of the branched-chain 2-oxo acid dehydrogenase complex only at low, physiological concentrations of these substrates (less than 0.025 mM).

Purification and properties of mouse thymus thymidylate synthase. Comparison of the enzyme from mammalian normal and tumour tissues

Mouse thymus thymidylate synthase has been purified to apparent electrophoretic homogeneity and compared with the enzyme from mouse tumour L1210 and Ehrlich ascites carcinoma cells. The enzyme is a dimer composed of 35,000 mol. wt monomers. Mouse thymus and tumour enzymes exhibit allosteric properties reflected by cooperative binding of both dUMP and 5-fluoro-dUMP. Activation energy for the reaction, catalyzed by thymidylate synthase from mouse tumour but not from mouse thymus, lowers at temperatures above 34 degrees C, reflecting a change of rate-limiting step in dTMP formation. MgATP at millimolar concentrations inhibits mouse thymus enzyme.