SEARCH · PubMed Health

Results for “PAM”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 829 records · Page 46Linked to original sources

PubMed1986

Kinetic investigations into the interactions of aprophen with cholinesterases and a carboxylesterase.

Acetylcholinesterases, butyrylcholinesterases, and carboxylesterases appear to form kinetically a homologous enzyme series with respect to many substrates and inhibitors. The present paper evaluates the interaction of aprophen with acetylcholinesterases, butyrylcholinesterases, and carboxylesterases with respect to protecting the enzyme from organophosphate and carbamate inhibition, accelerating pralidoxime iodide (2-PAM) regeneration of the diisopropylphospho-enzyme, and comparing the inhibition and regeneration kinetics of a soluble mammalian acetylcholinesterase with that of bovine erythrocyte acetylcholinesterase. The irreversible inhibition kinetics of diisopropyl fluorophosphate (DFP) and eserine inhibition of fetal bovine serum acetylcholinesterase were typical of other acetylcholinesterases as indicated by the bimolecular inhibition rate constants, ki, of 7.7 +/- 1.3 X 10(4) M-1 min-1 and 2.9 +/- 1.7 X 10(6) M-1 min-1, respectively. Similarly, the bimolecular regeneration rate constant, kr, for 2-PAM regeneration of the diisopropylphospho-acetylcholinesterase was 14.7 M-1 min-1. The bimolecular rate constants, ki and kr, were not statistically perturbed when the reaction was monitored in the presence of aprophen with the fetal bovine serum acetylcholinesterase. Human serum butyrylcholinesterase was partially protected from DFP inhibition by aprophen with no detectable change in the bimolecular inhibition rate constant, ki. The regeneration of the diisopropylphospho-butyrylcholinesterase by 2-PAM was accelerated in the presence of aprophen by a factor of 2.7 over that of 2-PAM alone (8.4 +/- 2.2 M-1 min-1 to 23.1 +/- 2.6 M-1 min-1 respectively). Neither the inhibition (DFP) nor the regeneration (2-PAM) kinetics observed for the carboxylesterase was perturbed by the presence of aprophen.

Acetylcholinesterase↗

PubMed1990

Mechanisms of in vitro immunosuppression by hepatocyte-generated cyclophosphamide metabolites and 4-hydroperoxycyclophosphamide.

Cyclophosphamide (CY) is metabolized to 4-hydroxy-CY which spontaneously breaks down to the reactive intermediates, phosphoramide mustard (PAM) and acrolein. The alkylating property of PAM is thought to mediate the anti-proliferative and cytotoxic actions of CY. Acrolein is known to bind sulfhydryl groups of cellular molecules and may contribute to the action of CY. However, the role of acrolein in the CY-induced immunosuppression remains unclear. The results of studies in which a hepatocyte co-culture system was used suggest that acrolein may play an important role in the cytotoxic action of CY, whereas those investigations using activated derivatives of CY indicate that acrolein is not an important factor. Thus, both approaches of CY exposure were utilized in the present study. Splenocytes of B6C3F1 mice were incubated with syngeneic isolated hepatocytes and CY or with 4-hydroperoxycyclophosphamide (4-HC) (which spontaneously decomposes to 4-hydroxy-CY). The in vitro antibody forming cell (AFC) response was found to be suppressed with both methods of exposure to CY metabolites. The addition of DNA to bind extracellular PAM was ineffective in preventing the suppression produced by hepatocyte-activated CY. However, it was also observed that DNA was able to attenuate the PAM-induced suppression. The sulfhydryl compounds 2-mercaptoethanesulfonate (MESNA) (15 microM) or reduced glutathione (GSH) (1 mM) inhibited the suppression of the AFC response of splenocytes incubated with CY and mouse hepatocytes. The suppression produced by 4-HC, however, was not affected by MESNA and only slightly inhibited by GSH. Similarly, the PAM-induced suppression was not affected by MESNA and slightly attenuated with GSH. In contrast, both MESNA and GSH were very effective in abrogating the acrolein-induced suppression, whereas DNA was ineffective. The findings of this study suggest that in the hepatocyte co-culture system, the immunosuppressive actions of CY are mediated by acrolein generated outside of the splenocyte, whereas the 4-HC induced suppression is not mediated by extracellular acrolein. Thus, this difference may explain the contradictory findings of previous studies that used different means of exposing cells to activated CY.

Acrolein↗

PubMed1985

Lysosomal enzyme activity in pulmonary alveolar macrophages, peritoneal macrophages, and blood mononuclear leukocytes in the hypothyroid rat.

Chronic hypothyroidism can result in an increased susceptibility to severe pulmonary or genitourinary tract infections. We postulate that decreased lysosomal activity in the pulmonary alveolar macrophage (PAM), peritoneal macrophage, and mononuclear leukocyte may be a factor which results in the impaired response to infections in hypothyrosis. In this study rats underwent total thyroidectomy and had their PAMs, peritoneal macrophages, and mononuclear leukocytes analyzed after 4, 8, and 12 weeks. The total lysosomal activity (postnuclear homogenate + lysosomal-rich cell fraction) of PAMs was 50% of age-matched controls. Peritoneal macrophage lysosomal enzyme activity was 25-30% of control activity. In separate experiments, rats were administered physiologic replacement of triiodothyronine (T3) 8 weeks after thyroidectomy. This resulted in PAM and peritoneal macrophage lysosomal enzyme activity similar to control activity. Mononuclear leukocyte lysosomal enzyme activity from hypothyroid rats showed decreases in only one of the three enzymes monitored (beta-glucuronidase). Hypothyroidism did result in a decrease in total number of mononuclear leukocytes harvested per animal. Administration of T3 resulted in mononuclear leukocyte beta-glucuronidase activity similar to euthyroid rats (44 +/- 8 U/mg protein vs 42 +/- 3 U/mg protein). In summary, hypothyroidism in the rat results in decreases in subcellular lysosomal enzyme activity in PAMs, peritoneal macrophages, and mononuclear leukocytes.

Animals↗

PubMed1986

Modulation of natural killer cell function by human alveolar macrophages.

Lymphocyte natural killer (NK) activity appears to be important in resistance against viral infection and malignancy. Since pulmonary alveolar macrophages (PAM) derived from nonsmokers suppress NK activity in vitro, we asked if PAM derived from smokers modulated NK activity in a similar fashion. Bronchoalveolar lavage cells (BLC) were obtained from healthy nonsmokers and healthy smokers by bronchoalveolar lavage. Increasing numbers of BLC were cocultured with a fixed ratio of monocyte-depleted peripheral blood lymphocytes (PBL) and Cr51-labeled K562 tumor target cells (PBL:K562, ratio 25:1; BLC:PBL ratios ranging from 0.02:1 to 1:1). Increasing numbers of BLC progressively suppressed the ability of either autologous or homologous PBL to lyse tumor targets. Smoker and nonsmoker BLC inhibited NK activity of homologous lymphocytes with similar potency. Suppression of NK activity by BLC was not reversed by the addition of indomethacin or catalase to cell cultures. Furthermore, suppression could not be reproduced by performing cytotoxicity assays in the presence of BLC culture supernatants. Lymphocytes boosted to high levels of NK activity by preincubation with alpha-interferon or interleukin-2 were still susceptible to suppression by BLC. Thus, PAM derived from smokers efficiently suppress lymphocyte NK activity, and the degree of suppression increases as the ratio of PAM to lymphocytes increases. Since smoking causes a bronchoalveolar accumulation of PAM, these inhibitory cells may result in profound local suppression of NK activity in smoker's lungs.

Adult↗

PubMed1982

Macrophage fibrinolytic activity: identification of two pathways of plasmin formation by intact cells and of a plasminogen activator inhibitor.

Endotoxin-stimulated macrophages hydrolyze fibrin by a plasmin-mediated process in the absence of detectable soluble plasminogen activator (PAs). The data show that macrophages also activate plasmin by a membrane-associated plasminogen activator (PAm). In the presence of endotoxin, PAm activity increases, and plasmin is formed only by PAm. In addition, endotoxin stimulates macrophages to secrete a proteinase inhibitor that blocks PAs activity but not PAm or plasmin activity. The increased PAm activity and the PA inhibitor secretion in response to endotoxin explains the ability of intact macrophages to hydrolyze fibrin in the absence of detectable PAs. Endotoxin, 100 ng/ml, induced an intracellular PA inhibitor in cultured macrophages, and this correlated with accumulation of inhibitor in medium over the cells. The intracellular PA inhibitor was found to be 50--60 kilodaltons by gel chromatography, to be of anionic charge at pH 7.4 and to inhibit urokinase esterolytic and proteolytic activity but not preformed plasmin. These results define two pathways of plasmin formation by intact macrophages and identify the macrophage cell surface as a site of PA activity relatively protected from soluble proteinase inhibitors.

Animals↗

PubMed1986

Phagocytosis and intracellular killing of Pasteurella multocida by porcine alveolar macrophages after infection with pseudorabies virus.

The purpose of this study was to determine if pseudorabies virus (PrV) interfered with normal alveolar macrophage phagocytic functions. Porcine alveolar macrophages (PAM) obtained by pulmonary lavage were exposed to PrV. At 1 hour postinfection, cells were challenged with Pasteurella multocida labeled with 3[H] thymidine. The phagocytosis assay was performed by measuring total radioactivity 1 hour after Pm challenge in a soft-beta spectrophotometer. Intracellular killing was measured by counting viable bacteria 3 hours after P. multocida challenge. Phagocytic values of PrV-infected and control PAM ranged from 11% to 20%, a non-significant difference. Values for intracellular killing for PrV-infected PAM ranged from 7.1 X 10(5) to 1 X 10(6) in contrast to 5.1 X 10(1) to 1.8 X 10(2) for the control PAM. This difference in killing function was significantly lower in PrV-infected PAM than in control cells (P less than 0.01). This alteration of macrophage function may be a factor in the pathogenesis of PrV-Pm mediated pneumonia in pigs.

Animals↗

PubMed1985

Effect of melphalan administration on the activity of natural killer and natural cytotoxic spleen cells of normal and tumor-bearing mice.

The effect of melphalan (L-PAM; L-phenylalanine mustard) administration on natural killer (NK) and natural cytotoxic (NC) activities of spleen cells from normal noninoculated BALB/c mice and mice bearing large MOPC-315 plasmacytoma tumors was investigated. Injection of L-PAM (7.5 or 15.0 mg/kg) had no effect on NK and NC activities of spleen cells from normal mice whereas stimulation by PHA was markedly suppressed. NK activity was markedly suppressed in spleens of tumor-bearing mice whereas NC activity was not affected. Therapy with L-PAM of tumor-bearing mice led to transient recovery of NK activity which was possibly related to the effect of L-PAM on macrophage suppressive activity on NK cells. It is concluded that NK and NC cell activities and the response to PHA stimulation are selectively affected by L-PAM administration.

Animals↗

PubMed1996

Peptide amidating activity in human bronchoalveolar lavage fluid.

Monitoring respiratory epithelial biology may reveal individuals with incipient lung cancer. The expression of neuroendocrine (NE) markers in pulmonary epithelium is thought to be central to lung development, repair of injury and may contribute to carcinogenesis. In this study, we evaluate several candidate NE markers to determine the feasibility of prospective analysis of clinical specimens. The potential NE markers include the enzyme L-DOPA decarboxylase (DDC), the neuropeptide gastrin releasing peptide (GRP), and peptidyl-glycine alpha-amidating monooxygenase (PAM), the bifunctional enzyme responsible for the final bioactivation step of many neuropeptides. A comparison of PAM activity and DDC levels in 30 lung cancer cell lines indicated that peptide amidating activity may be an indicator of NE status. Bronchoalveolar lavage (BAL) fluid from subjects at risk of developing second primary lung cancer and from volunteers was obtained. The activity of the first PAM enzyme, peptidylglycine alpha-hydroxylating monooxygenase (PHM), ranged from not detectable to 507 pmol/h/mg protein in 57 specimens. The second PAM enzyme, peptidylamidoglycolate lyase (PAL), ranged from not detectable to 414 pmol/h/mg protein in 56 specimens. Using cluster analysis by the average linkage method, a group of enzyme values with PHM greater than 230 pmol/h/mg protein was determined. Long-term follow-up of these patients for new second primary lung cancers may help to determine the potential predictive value of PAM detected in the BAL fluid.

Biomarkers, Tumor↗

PubMed1988

Tumoricidal and immunomodulatory activities of drugs and implications for therapy of mice bearing a late stage MOPC-315 plasmacytoma.

The effectiveness of a relatively low dose of cyclophosphamide (15 mg/kg CY), melphalan (2.5 mg/kg L-PAM) or the monofunctional form of CY (150 mg/kg MoCY) for the cure of mice bearing a large primary s.c. MOPC-315 tumor and extensive metastases has been shown to be dependent on the cooperation of the drugs' tumoricidal activity with T-cell-dependent antitumor immunity, the latter facilitated by the drug's immunomodulatory activity. Here, we have compared the curative effectiveness of three additional drugs: methyl nitrosourea (MNU), hydroxyurea (OH-urea) and bis-chloroethyl nitrosourea (BCNU). Among these drugs, only a relatively low dose of BCNU (15-20 mg/kg) was effective in curing most mice (85%) bearing a large, late stage tumor. A higher dose of BCNU (40 mg/kg, LD10) was much less effective. After an optimal dose of BCNU, the proliferative capacity of the tumor cells 24 h after therapy was reduced by greater than 97%. However, viable tumorigenic cells were still present in the primary tumor and enhanced T-cell-dependent antitumor immunity was necessary for their eradication. The cured mice were resistant to tumor rechallenge. When a low curative dose of L-PAM was followed by OH-urea, the therapeutic effectiveness was not affected, but when this dose of L-PAM was followed by a high nontoxic dose of MNU (100-150 mg/kg), the therapeutic effectiveness was diminished even though MNU was highly tumoricidal (i.e. greater than 99% inhibition of proliferative activity). Thus, BCNU appears to be similar to CY, L-PAM and MoCY in its mechanism of MOPC-315 tumor eradication. The alkylating activity of CY, L-PAM, MoCY and BCNU appears to be critical for their combined tumoricidal and immunomodulatory effects. Since BCNU is the simplest of these four drugs with respect to metabolic pathway, a further study with BCNU and related constructs may shed some light on the biochemical mechanisms of their mode of action. At least one reason for the ineffectiveness of OH-urea or MNU at either low or nontoxic high doses was poor tumoricidal or immunomodulatory activity, respectively. Thus, it seems important to consider both the tumoricidal and immunomodulatory activities of drugs when developing regimens for effective chemotherapy.

Adjuvants, Immunologic↗

PubMed1994

Prediction of failure to survive following in-hospital cardiopulmonary resuscitation: comparison of two predictive instruments.

The purpose of this study is to compare two clinical predictive rules, the pre-arrest-morbidity (PAM) index and the prognosis-after-resuscitation (PAR) score, which predict failure to survive following in-hospital cardiopulmonary resuscitation (CPR). The study population consisted of 274 consecutive adult patients who underwent CPR at University College Hospital in Galway, Ireland over a 2-year period. The PAM and PAR scores were calculated from the most recent data available for each variable prior to cardiac arrest. Performance of the predictive scores was compared using Student's t-test, Pearson chi-square, Fisher's exact test, and receiver-operating characteristic (ROC) curves where appropriate. The PAM index identified 23 patients with a score > 4, while the PAR score identified 59 patients with a score > 5, none of whom survived. The sensitivity of the PAR score for the prediction of failure to survive was 23.7%, while that of the PAM index was 9.2%; neither index incorrectly identified a patient as a non-survivor who eventually survived. The PAR score also had a greater area under the ROC curve, although this difference was not statistically significant (P = 0.07). In summary, the PAR score performed better than the PAM index in the identification of patients who are unlikely to survive following CPR. Although further confirmation is necessary, it may provide useful prognostic information to physicians and patients involved with decisions about do-not-resuscitate orders.

Adolescent↗

PubMed1993

Coclastogenicity of ethanol with cigarette smoke in rat erythroblasts and anticlastogenicity in alveolar macrophages.

A series of experiments was carried out to assess cytotoxic and cytogenetic effects in bone marrow polychromatic erythrocytes (PCE) and pulmonary alveolar macrophages (PAM) resulting from individual or combined exposure of male BD6 rats to ethanol, cigarette smoke and Aroclor 1254. Addition of 5% ethanol to drinking water did not affect the micronucleus frequency but consistently enhanced the proportion of polynucleated PAM. Moreover, the higher concentration used (10%) was cytotoxic in the bone marrow. Whole-body exposure to cigarette smoke elevated the micronucleus frequency in both PCE (4.0-4.4-fold) and PAM (2.0-3.6-fold) and enhanced the frequency of polynucleated PAM. After 3 weeks of combined exposure, ethanol produced contrasting effects in smoke-exposed rats, i.e. an increase of micronuclei in PCE and a decrease in PAM. An i.p. injection of Aroclor 1254 was per se devoid of any influence on the monitored parameters but tended to attenuate the cytotoxic and cytogenetic changes produced by cigarette smoke or ethanol in both types of cell.

Animals↗

PubMed1984

Enhancement of melphalan cytotoxicity in vivo and in vitro by inhibitors of poly (ADP-ribose) polymerase.

In these preliminary experiments, we have found enhanced cell killing by the bifunctional alkylating agent L-phenylalanine mustard (L-PAM) in the presence of inhibitors of poly (ADP-ribose) polymerase (ADPRP) in vitro. In vivo enhancement of the tumoricidal effects of L-PAM was observed with the ADPRP inhibitor nicotinamide (1000 mg/kg), although enhanced myelosuppression was also demonstrated. Nicotinamide also increased the plasma elimination half-life of L-PAM by a factor of at least 2. This alteration of L-PAm pharmacokinetics makes it difficult to assess the role that ADPRP inhibition plays in the enhancement of L-PAM tumor cell killing in vivo.

Animals↗

PubMed1992

Studies of the amplification of carbaryl toxicity by various oximes.

The administration of 2-pyridine aldoxime methyl chloride (2-PAM Cl) is a standard part of the regimen for treatment of human overexposure to many organophosphorus pesticides and nerve agents. However, some literature references indicate that poisoning by carbaryl (1-naphthyl N-methyl carbamate), an insecticide in everyday use, is aggravated by the administration of 2-PAM Cl. This effect has been reported in the mouse, rat, dog and man. We have found that the inhibition of both eel acetylcholinesterase (eel AChE, EC 3.1.1.7) and human serum cholinesterase (human BuChE, EC 3.1.1.8) by carbaryl was enhanced by several oximes. Based on 95% confidence limits the rank order of potentiation with eel AChE was TMB-4 = Toxogonin > HS-6 = HI-6 > 2-PAM Cl. By the same criterion, the rank order of potentiation with human BuChE was TMB-4 > Toxogonin > HS-6 = 2-PAM Cl. Carbaryl-challenged mice also reflected a potentiation since TMB-4 exacerbated the toxicity more than 2-PAM Cl. Our hypothesis is that certain oximes act as allosteric effectors of cholinesterases in carbaryl poisoning, resulting in enhanced inhibition rates and potentiation of carbaryl toxicity.

Animals↗

PubMed2005

Muscle atrophy and bone loss after 90 days' bed rest and the effects of flywheel resistive exercise and pamidronate: results from the LTBR study.

Muscle atrophy and bone loss pose substantial problems for long-term space flight and in clinical immobilization. We therefore tested the efficacy of flywheel resistive exercise and pamidronate to counteract such losses. Twenty five young healthy males underwent strict bed rest with -6 degrees head-down tilt for 90 days. Subjects were randomized into an exercise group that practiced resistive exercise with a 'flywheel' (FW) device every 2-3 days, a pamidronate group (Pam) that received 60 mg pamidronate i.v. 14 days prior to bed rest and a control group (Ctrl) that received none of these countermeasures. During the study, Ca(++) and protein intake were controlled. Peripheral quantitative computed tomography (pQCT) was used to assess bone mineral content (BMC) and muscle cross sectional area (mCSA) of calf and forearm. Measurements were taken twice during baseline data collection, after 28 and after 89 days bed rest, and after 14 days recovery. On the same days, urinary Pyridinoline excretion and serum levels of alkaline phosphatase, Ca(++) and PTH were measured. Pre-study exercise habits were assessed through the Freiburg questionnaire. Losses in calf mCSA were significantly reduced in FW (Ctrl: -25.6% +/- 2.5% Pam: -25.6% +/- 3.7%, FW: -17.3% +/- 2.7%), but not in the forearm mCSA (Ctrl: -6.4% +/- 4.33%, Pam: -7.7% +/- 4.1%, FW: -7.6% +/- 3.3%). Both diaphyseal and epiphyseal BMC losses of the tibia were mitigated in Pam and FW as compared to Ctrl, although this was significant only at the diaphysis. Inter-individual variability was significantly greater for changes in BMC than in mCSA, and correlation of BMC losses was poor among different locations of the tibia. A significant positive correlation was found between change in tibia epiphyseal BMC and serum cortisol levels. These findings suggest that both countermeasures are only partly effective to preserve BMC (FW and Pam) and mCSA (FW) of the lower leg during bed rest. The partial efficacy of flywheel exercise as well as the bones' response to unloading per se underlines the importance of mechanical stimuli. The huge variability of BMC changes, however, suggests that other factors affect changes in whole-bone strength following acute mechanical disuse.

Adult↗

PubMed2005

Polyacrylamide sorption opportunity on interlayer and external pore surfaces of contaminant barrier clays.

Physico-chemical interactions among polymer molecules in aqueous solution and clay mineralogical/textural characteristics influence the sorption of polymer molecules on clay barrier minerals. Amendment of potentially unstable barrier clays with aqueous polymers can improve barrier material resistance to environmental stresses during service. In this research, the ability of molecular coils of polyacrylamide (PAM) to overlap in solution and to enter interlayer space in Na-montmorillonite (specific surface=31.82+/-0.22 m2 g(-1)) and kaolinite (specific surface=18+/-2 m2 g(-1)) were analyzed theoretically and experimentally, using solution viscosity measurements, and X-ray diffractometry. Experimental data on two theoretical indices: relative size ratio (RSR); and molecular availability (Ma) that are formulated to scale polymer molecular sorption on clay interlayer, indicate that the sorption of PAM A (Mw=4000000) and PAM B (Mw=7000000) does not produce any significant change in the d-spacing of both clay minerals. Although the negative Ma values of -3.51 g l(-1) for PAM A and -3.88 g l(-1) for PAM B indicate high levels of entanglement of polymer molecular coils in solution, sorption data confirm that the entangled coils are still able to sorb onto Na-montmorillonite highly and kaolinite to a lesser extent.

Acrylic Resins↗

PubMed2004

Curing depth of (polyacid-modified) composite resins determined by scraping and a penetrometer.

OBJECTIVES: The present study aimed to compare the curing depth of polyacid-modified composite resins (PAM-C) and some representative composite resins as a function of shade and post-cure using a scraping method and a penetrometer. METHODS: The curing depth of the PAM-C Hytac, F2000, Glasiosite, Dyract, Dyract AP, and Compoglass F and of the composite resins Durafill VS and Z100 were determined for shade A2 and A4 using a scraping method based on ISO 4049:2000 and a digital penetrometer. Samples were light-cured (800 mW/cm2 at 40 s) in bulk in split stainless steel molds. Immediately after light-curing or after a 24 h post-cure, the height of the cylinder of cured material was measured and taken as the curing depth. RESULTS: For both test methods, the curing depth was independent of post-cure (P > or = 0.05) but differed significantly among materials and shade (P<0.001). Moreover, there was a significant interaction between the latter (P<0.001). Regression analysis generally demonstrated that there was no significant systematic or proportional difference between the test methods. The curing depths of the PAM-C F2000 and Glasiosite were comparable to that of the hybrid composite Z100, but greater than the curing depth of the microfilled composite Durafill VS. The PAM-C Dyract AP, Dyract, Compoglass F and Hytac had a curing depth smaller than that of the microfilled composite. SIGNIFICANCE: The scraping method based on ISO 4049:2000 and a digital penetrometer give comparable curing depths for PAM-C. The curing depth greatly varies among the materials and can be considerably smaller than that of a microfilled composite resin. Shade A2 results in significantly greater values for the curing depth compared to shade A4, the effect depending quantitatively on the formulation of the material.

Color↗

PubMed2006

Genetic characterization of the natural hybrid species Phytophthora alni as inferred from nuclear and mitochondrial DNA analyses.

The different subspecies of Phytophthora alni, P. alni subsp. alni (Paa), P. alni subsp. uniformis (Pau), and P. alni subsp. multiformis (Pam), are recent and widespread pathogens of alder in Europe. They are believed to be a group of emergent heteroploid hybrids between two phylogenetically close Phytophthora species. Nuclear and mitochondrial DNA analyses were performed, using a broad collection of P. alni and two closely related species, P. cambivora and P. fragariae. Paa possesses three different alleles for each of the nuclear genes we studied, two of which are present in Pam as well, whereas the third matches the single allele present in Pau. Moreover, Paa displays common mtDNA patterns with both Pam and Pau. A combination of the data suggests that Paa may have been generated on several occasions by hybridization between Pam and Pau, or their respective ancestors. Pau might have P. cambivora as a species ancestor, whereas Pam seems to have either been generated itself by an ancient reticulation or by autopolyploidization.

Alleles↗

PubMed2005

Improved dewatering behavior of clay minerals dispersions via interfacial chemistry and particle interactions optimization.

Orthokinetic flocculation of clay dispersions at pH 7.5 and 22 degrees C has been investigated to determine the influence of interfacial chemistry and shear on dewatering and particle interactions behavior. Modification of pulp chemistry and behavior was achieved by using kaolinite and Na-exchanged (swelling) smectite clay minerals, divalent metal ions (Ca(II), Mn(II)) as coagulants and anionic polyacrylamide copolymer (PAM A) and non-ionic polyacrylamide homopolymer (PAM N) as flocculants. The pivotal role of shear, provided by a two-blade paddle impeller, was probed as a function of agitation rate (100-500 rpm) and time (15/60 s). Particle zeta potential and adsorption isotherms were measured to quantify the interfacial chemistry, whilst rheology and cryogenic SEM were used to investigate particle interactions and floc structure and aggregate network, respectively. Osmotic swelling, accompanied by the formation of "honeycomb" particle network structure and high yield stress, was produced by the Na-exchanged smectite, but not kaolinite, dispersions. Dispersion of the clay particles in 0.05 M Ca(II) or Mn(II) solution led to a marked reduction in particle zeta potential, complete suppression of swelling, honeycomb network structure collapse and a concomitant reduction in shear yield stress of smectite pulps. Optimum conditions for improved, orthokinetic flocculation performance of negatively charged clay particles, reflecting faster settling flocs comprised (i) coagulation, (ii) moderate agitation rate, (iii) shorter agitation time, and (iv) anionic rather than non-ionic PAM. The optimum dewatering rates were significantly higher than those produced by standard, manual-mixing flocculation techniques (plunging and cylinder inversion) commonly used in industry for flocculant trials. The optimum flocculation conditions did not, however, have a significant impact on the final sediment solid content of 20-22 wt%. Further application of shear to pre-sedimented pulps improved consolidation by 5-7 wt% solid. Higher shear yield stresses and greater settling rates were displayed by PAM A based than PAM N based pulps and this is attributed to the former's more expanded interfacial conformation and greater clay particles bridging ability. It appears that the intrinsic clay particles' physico-chemical properties and interactions limit compact pulp consolidation.

Journal Article↗