RESUMO
PURPOSES: To evaluate the impact of percutaneous cholecystostomy (PC) on severe acute cholecystitis (AC). METHODS: According to the ICD-9 classification, we retrospectively retrieved medical records of patients discharged with a diagnosis of AC from January 2007 to December 2016 at our hospital. Patients were then stratified according to the Tokyo 2013 (TG 13) AC severity criteria. Grade III AC was diagnosed according to the TG 13 criteria. Indications for PC were failure of optimal medical treatment within 48 h, worsening of clinical condition within early medical treatment, patients unfit for upfront surgery and patient's preference. Ascites was considered a contraindication to PC while coagulopathy was considered a minor contraindication. Primary end points were: clinical improvement, morbidity and related mortality. Secondary endpoints were AC recurrences and elective laparoscopic cholecystectomies (LS). Response was evaluated by clinical and blood test improvement. Morbidity was evaluated according to the Dindo-Clavien scale. RESULTS: A total of 117 eligible patients were diagnosed as grade III AC. Of these, 29 (24.7%) underwent PC. The procedure was completed in all cases. Overall morbidity rate was 20.6%. Main complication was the drainage dislodgement due to involuntary patient's movement. Overall mortality was 17.2% but no causes of death were dependent upon the procedure. Clinical improvement was reported in 95.5% of surviving patients. CONCLUSION: This study confirms that PC is a valuable tool in the treatment of severe AC. Randomized trials are needed to clarify the criteria for patient selection and to optimize the timing for both cholecystostomy and cholecystectomy.
Assuntos
Colecistite Aguda/cirurgia , Colecistostomia/métodos , Drenagem/métodos , Idoso , Idoso de 80 Anos ou mais , Colecistite Aguda/fisiopatologia , Tomada de Decisão Clínica , Feminino , Seguimentos , Humanos , Tempo de Internação/estatística & dados numéricos , Masculino , Pessoa de Meia-Idade , Guias de Prática Clínica como Assunto , Estudos Retrospectivos , Fatores de Tempo , Resultado do TratamentoRESUMO
This study investigated the involvement of estrogen receptors alpha and beta in estradiol-induced enhancement of hippocampal neurogenesis in the adult female rat. Subtype selective estrogen receptor agonists, propyl-pyrazole triol (estrogen receptor alpha agonist) and diarylpropionitrile (estrogen receptor beta agonist) were examined for each receptor's contribution, individual and cooperative, for estradiol-enhanced hippocampal cell proliferation. Estradiol increases hippocampal cell proliferation within 4 h [Ormerod BK, Lee TT, Galea LA (2003) Estradiol initially enhances but subsequently suppresses (via adrenal steroids) granule cell proliferation in the dentate gyrus of adult female rats. J Neurobiol 55:247-260]. Therefore, animals received s.c. injections of estradiol (10 microg), propyl-pyrazole triol and diarylpropionitrile alone (1.25, 2.5, 5.0 mg/0.1 ml dimethylsulfoxide) or in combination (2.5 mg propyl-pyrazole triol+2.5 mg diarylpropionitrile/0.1 ml dimethylsulfoxide) and 4 h later received an i.p. injection of the cell synthesis marker, bromodeoxyuridine (200 mg/kg). Diarylpropionitrile enhanced cell proliferation at all three administered doses (1.25 mg, P<0.008; 2.5 mg, P<0.003; 5 mg, P<0.005), whereas propyl-pyrazole triol significantly increased cell proliferation (P<0.0002) only at the dose of 2.5 mg. Our results demonstrate both estrogen receptor alpha and estrogen receptor beta are individually involved in estradiol-enhanced cell proliferation. Furthermore both estrogen receptor alpha and estrogen receptor beta mRNA was found co-localized with Ki-67 expression in the hippocampus albeit at low levels, indicating a potential direct influence of each receptor subtype on progenitor cells and their progeny. Dual receptor activation resulted in reduced levels of cell proliferation, supporting previous studies suggesting that estrogen receptor alpha and estrogen receptor beta may modulate each other's activity. Our results also suggest that a component of estrogen receptor-regulated cell proliferation may take place through alternative ligand and/or cell-signaling mechanisms.
Assuntos
Proliferação de Células/efeitos dos fármacos , Giro Denteado/citologia , Receptor alfa de Estrogênio/agonistas , Receptor beta de Estrogênio/agonistas , Nitrilas/farmacologia , Propionatos/farmacologia , Pirazóis/farmacologia , Análise de Variância , Animais , Bromodesoxiuridina/metabolismo , Contagem de Células/métodos , Relação Dose-Resposta a Droga , Proteínas do Domínio Duplacortina , Receptor alfa de Estrogênio/genética , Receptor beta de Estrogênio/genética , Feminino , Proteína Glial Fibrilar Ácida/metabolismo , Imuno-Histoquímica/métodos , Hibridização In Situ/métodos , Antígeno Ki-67/metabolismo , Proteínas Associadas aos Microtúbulos/metabolismo , Neuropeptídeos/metabolismo , Fenóis , RatosRESUMO
The bactericidal activities and post-antibiotic effects of BMS-284756 (T-3811ME), levofloxacin, and ciprofloxacin were evaluated against a methicillin-susceptible and a methicillin-resistant Staphylococcus aureus strain. Minimum inhibitory concentrations (MICs), minimum bactericidal concentrations, post-antibiotic effects, and post-antibiotic sub-MIC effects were determined and time-kill studies were performed for BMS-284756, levofloxacin, and ciprofloxacin. At 4-times and 10-times the MIC, time-kill kinetics over 3 h and over 24 h were similar for all three quinolones when effects were considered as multiples of the MIC. All three quinolones achieved a 3 log10 reduction in cfu/ml within 2 h. At 10-times the MIC, the post-antibiotic effects of BMS-284756, levofloxacin, and ciprofloxacin were 1.6-2.6 h for the methicillin-susceptible Staphylococcus aureus strain and 1.5-1.9 h for the methicillin-resistant Staphylococcus aureus strain. When actual concentrations were considered, BMS-284756 achieved results comparable to levofloxacin and ciprofloxacin at concentrations nearly 10-fold less. When relating the pharmacokinetic properties of the three quinolones to their in vitro activities, the resulting Cmax/MIC and AUC/MIC ratios were. respectively, 120-240.7 and 1,321.7-2,643 for BMS-284756, 22.8 and 190 for levofloxacin, and 5.9-11.9 and 54.8-109.6 for ciprofloxacin. The greater in vitro activity and favorable human pharmacokinetics of BMS-284756 may translate to improved clinical effectiveness of this agent compared to currently marketed quinolones.
Assuntos
Anti-Infecciosos/farmacologia , Ciprofloxacina/farmacologia , Fluoroquinolonas , Indóis , Levofloxacino , Resistência a Meticilina , Ofloxacino/farmacologia , Quinolonas , Staphylococcus aureus/efeitos dos fármacos , Atividade Bactericida do Sangue , Resistência Microbiana a Medicamentos , Humanos , Meticilina/farmacologia , Testes de Sensibilidade Microbiana , Sensibilidade e EspecificidadeRESUMO
A paralog (intraspecies homolog) of the Saccharomyces cerevisiae YEF3 gene, encoding elongation factor-3, has been sequenced in the course of the yeast genome project, and identified by database searching; this gene has been designated HEF3. Bioinformatic and Northern blot analysis indicate that the HEF3 gene is not expressed during vegetative growth. Deletion of the HEF3 gene reveals no growth defects, nor any defects in mating or sporulation. A high copy 2 mu clone of HEF3 was constructed, and was shown to be unable to complement a null allele of yef3. Finally, an in vitro assay for ribosome-stimulated ATPase activity was performed with isogenic HEF3 and delta hef3 strains; no difference in biochemical activity could be detected in these strains. From these results, we conclude that the HEF3 gene does not encode a functional homolog of YEF3.
Assuntos
Sequência Conservada/genética , Proteínas Fúngicas , Genes Fúngicos/genética , Fatores de Alongamento de Peptídeos/genética , Proteínas de Saccharomyces cerevisiae , Saccharomyces cerevisiae/genética , Adenosina Trifosfatases/metabolismo , Sequência de Aminoácidos , Northern Blotting , Clonagem Molecular , Biologia Computacional , Bases de Dados Factuais , Expressão Gênica , Genes Essenciais/genética , Teste de Complementação Genética , Vetores Genéticos/genética , Fenótipo , Plasmídeos/genética , RNA Mensageiro/análise , RNA Mensageiro/genética , Proteínas Recombinantes de Fusão/genética , Ribossomos/metabolismo , Saccharomyces cerevisiae/enzimologia , Alinhamento de Sequência , Deleção de Sequência , Homologia de Sequência de AminoácidosRESUMO
The fungal metabolite trichodimerol (BMS-182123) has demonstrated inhibition of lipopolysaccharide (LPS)-stimulated tumor necrosis factor-alpha (TNF-alpha) secretion in various in vitro macrophage models (human and murine) including primary and tumor cell lines. When challenged with LPS, differentiated THP-1 monocytic cells secrete elevated levels of the cyclooxygenase products prostaglandin E2 (PGE2), thromboxane B2, and prostaglandin F2alpha (PGF2alpha). Studies directed at elucidating the mechanism of action of BMS-182123 as a TNF-alpha inhibitor revealed that the compound has a profound inhibitory effect on prostanoid secretion in response to LPS challenge. The key enzymes in prostaglandin synthesis are the constitutive cyclooxygenase, prostaglandin H synthase-1 (PGHS-1), and the mitogen-induced cyclooxygenase (PGHS-2), which is induced upon LPS stimulation in THP-1 cells. BMS-182123 did not inhibit the cyclooxygenase activity of PGHS-1 in an in vitro assay, suggesting that inhibition is due to a blockade in synthesis of cyclooxygenase enzyme. Western blot analysis of microsomal pellets from THP-1 cells stimulated with LPS (with or without BMS-182123 pretreatment) provided convincing evidence that the inhibition of prostaglandin synthesis is a result of suppressed synthesis of PGHS-2 enzyme. Northern blot analysis of THP-1 RNA demonstrated that BMS-182123 inhibits the induction of PGHS-2 at the level of transcription.
Assuntos
Hidrocarbonetos Aromáticos com Pontes/farmacologia , Eicosanoides/metabolismo , Lipopolissacarídeos/antagonistas & inibidores , Monócitos/efeitos dos fármacos , Monócitos/metabolismo , Northern Blotting , Western Blotting , Cromatografia Líquida de Alta Pressão , Inibidores de Ciclo-Oxigenase/farmacologia , Dinoprostona/metabolismo , Humanos , Lipopolissacarídeos/farmacologia , Prostaglandina-Endoperóxido Sintases/biossíntese , Prostaglandina-Endoperóxido Sintases/metabolismo , RNA/análiseRESUMO
A rare case of double Pancoast tumor in a patient with metachronous primary cancer of the lung was treated with irradiation and operation. Both tumors were managed with pulmonary wedge resection and excision of involved chest wall. Six years after the first operation the patient is doing well without pain and respiratory failure.
Assuntos
Adenocarcinoma/complicações , Neoplasias Pulmonares/complicações , Segunda Neoplasia Primária/complicações , Síndrome de Pancoast/etiologia , Adenocarcinoma/diagnóstico por imagem , Adenocarcinoma/cirurgia , Humanos , Neoplasias Pulmonares/diagnóstico por imagem , Neoplasias Pulmonares/cirurgia , Masculino , Pessoa de Meia-Idade , Segunda Neoplasia Primária/diagnóstico por imagem , Segunda Neoplasia Primária/cirurgia , RadiografiaAssuntos
Guanidinas/farmacologia , Imunossupressores/farmacologia , Animais , Ciclosporina/farmacologia , Feminino , Humanos , Interleucina-2/metabolismo , Ativação Linfocitária/efeitos dos fármacos , Teste de Cultura Mista de Linfócitos , Camundongos , Camundongos Endogâmicos C57BL , Camundongos Endogâmicos DBA , Receptores de Interleucina-2/análise , Subpopulações de Linfócitos T/efeitos dos fármacos , Subpopulações de Linfócitos T/imunologia , Linfócitos T Citotóxicos/efeitos dos fármacosRESUMO
We determined the effects of two prostacyclin agonists (octimibate and BMY 42393) on the progression of the fatty streak in vivo and on macrophage function in vitro. Hamsters were fed chow plus 0.05% cholesterol and 10% coconut oil. Control hamsters were compared with animals receiving either octimibate (10 or 30 mg/kg per day) or BMY 42393 (30 mg/kg per day). After 10 weeks of treatment, octimibate decreased plasma total cholesterol and triglycerides by 43% and 32%, respectively. Neither agonist affected blood pressure or heart rate. Lesion-prone aortic arches were stained with hematoxylin and oil red O and examined en face. Compared with controls, octimibate and BMY 42393 on average decreased mononuclear cells attached to the luminal surface by 44% and reduced subendothelial macrophage-foam cell number by 56%, foam cell size by 38%, and fatty streak area by 63%. Since octimibate is a putative inhibitor of acyl coenzyme A cholesterol acyltransferase, we studied the effect of both agents on cholesteryl ester metabolism in murine macrophages. At 10 microM, octimibate and BMY 42393 decreased cholesteryl ester accumulation in macrophages by 90% and 41%, respectively. Octimibate inhibited cholesteryl ester synthesis by 96% and increased the rate of cholesteryl ester degradation by 52%. Both prostacyclin agonists reduced macrophage scavenger receptor-mediated uptake of acetylated low density lipoprotein by 24-66% and increased cyclic adenosine monophosphate levels. Octimibate and BMY 42393 inhibited the secretion of tumor necrosis factor by 80-88% when macrophages were activated with lipopolysaccharide. At 10 microM, both agents decreased human monocyte chemotaxis to N-formyl-methionyl-leucyl-phenylalanine by 64-79%. The in vitro results with octimibate and BMY 42393 are consistent with the low number of small foam cells quantified in vivo. We suggest that octimibate and BMY 42393 suppress monocyte-macrophage atherogenic activity and cytokine production and thus inhibit the development of early atherosclerosis.
Assuntos
Arteriosclerose/tratamento farmacológico , Epoprostenol/fisiologia , Hiperlipidemias/complicações , Imidazóis/uso terapêutico , Proteínas de Membrana , Oxazóis/uso terapêutico , Fenoxiacetatos/uso terapêutico , Receptores de Lipoproteínas , Animais , Aorta Torácica/patologia , Arteriosclerose/etiologia , Arteriosclerose/patologia , Quimiotaxia/efeitos dos fármacos , Ésteres do Colesterol/metabolismo , Cricetinae , Macrófagos/metabolismo , Masculino , Monócitos/efeitos dos fármacos , Monócitos/fisiologia , Receptores Imunológicos/metabolismo , Receptores Depuradores , Receptores Depuradores Classe B , Fator de Necrose Tumoral alfa/biossínteseRESUMO
The growth regulatory protein oncostatin M was initially discovered in macrophage-conditioned medium. We investigated the effects of oncostatin M on cultured rabbit aorta smooth muscle cells (SMCs) and found that the peptide stimulated an increase in the incorporation of [3H]thymidine into DNA. The magnitude of the stimulation was dependent on oncostatin M concentration and SMC confluency. In subconfluent cultures, 1-2 nM stimulated 4- to 5-fold increases in DNA synthesis after 20 hr. Other structurally related cytokines (granulocyte colony-stimulating factor, leukemia inhibitory factor, interleukin 6, ciliary neurotrophic factor) did not affect SMC DNA synthesis. After 5 or 8 days, oncostatin M caused a doubling in SMC number and also induced a transformed phenotype. The combination of oncostatin M and platelet-derived growth factor for 8 days resulted in a 4-fold increase in cell number, approximately the same increase in cell number as induced by the addition of 10% fetal calf serum. Further investigation suggested that the mitogenic effect of oncostatin M was in part due to tyrosine kinase activation. Within 1-2 min, the factor increased phosphotyrosine levels of several SMC proteins. In addition, detectable increases in diacylglycerol levels occurred within 2-5 min, reached 50% above control by 30 min, and remained elevated through 45 min of incubation with oncostatin M. SMC inositol phosphate levels were also elevated within 2 min and then returned to near control values by 20 min. Within 30 min, oncostatin M induced expression of the immediate-early gene EGR-1. These data indicate that oncostatin M may be an important, naturally occurring mitogen for vascular SMCs.
Assuntos
Citocinas/farmacologia , Mitógenos/farmacologia , Músculo Liso Vascular/efeitos dos fármacos , Peptídeos/farmacologia , Animais , Aorta/citologia , Divisão Celular/efeitos dos fármacos , Células Cultivadas , Desenvolvimento Muscular , Proteínas Musculares/metabolismo , Músculo Liso Vascular/crescimento & desenvolvimento , Oncostatina M , Fosforilação , Proteínas Tirosina Quinases/metabolismo , CoelhosRESUMO
Deoxyspergualin (DSG) is a potent immunosuppressant whose mechanism of action remains unknown. To elucidate its mechanism of action, an intracellular DSG binding protein was identified. DSG has now been shown to bind specifically to Hsc70, the constitutive or cognate member of the heat shock protein 70 (Hsp70) protein family. The members of the Hsp70 family of heat shock proteins are important for many cellular processes, including immune responses, and this finding suggests that heat shock proteins may represent a class of immunosuppressant binding proteins, or immunophilins, distinct from the previously identified cis-trans proline isomerases. DSG may provide a tool for understanding the function of heat shock proteins in immunological processes.
Assuntos
Guanidinas/metabolismo , Proteínas de Choque Térmico/metabolismo , Imunossupressores/metabolismo , Sequência de Aminoácidos , Humanos , Dados de Sequência Molecular , Ligação Proteica , Células Tumorais CultivadasRESUMO
Fifty-six patients with superior sulcus syndrome were evaluated at the First Surgical Department of the University of Padua between 1981 and 1990. Forty-two patients with the characteristic of Pancoast's tumor received preoperative irradiation and then en bloc resection of the tumor, chest wall, and adjacent structures. Seven lobectomies and 35 segmentectomies or wedge resections were performed. There was one early postoperative death. Median survival was 14 months, and actuarial survival was 25% at 5 years. Patients with pain relief had better 5-year survival (36.4%) than patients without pain relief (9%). We have no patients with vertebral invasion who survived more than 1 year. Of the five patients with subclavian artery invasion, only one survived more than 1 year. Of five patients with N2 disease, only one survived more than 1 year. Our results suggest that pain relief after irradiation is a good prognostic factor, whereas N2 involvement and vertebral body and great vessel invasion are ominous factors. Another ominous prognostic factor is the Claude Bernard-Horner syndrome even if it is not a contraindication to resection.
Assuntos
Adenocarcinoma/radioterapia , Adenocarcinoma/cirurgia , Carcinoma de Células Escamosas/radioterapia , Carcinoma de Células Escamosas/cirurgia , Carcinoma/radioterapia , Carcinoma/cirurgia , Síndrome de Pancoast/radioterapia , Síndrome de Pancoast/cirurgia , Adenocarcinoma/mortalidade , Adulto , Idoso , Carcinoma/mortalidade , Carcinoma de Células Escamosas/mortalidade , Terapia Combinada , Feminino , Humanos , Masculino , Pessoa de Meia-Idade , Manejo da Dor , Síndrome de Pancoast/mortalidade , Prognóstico , Dosagem Radioterapêutica , Fatores de TempoRESUMO
Recent evidence suggests the possibility that macrophages can influence lipoprotein metabolism. Therefore we investigated the ability of cultured macrophages to alter low density lipoprotein (LDL) uptake in a human liver cell line (HepG2). Conditioned media from phlogogenic-induced mouse peritoneal macrophages or from a human macrophage cell line stimulated with endotoxin increased HepG2 LDL uptake by as much as 60-70%. The increase was due, in part, to a significant macrophage-induced 40% increase in the number of LDL receptors per cell. Although macrophage conditioned media inhibited HepG2 cholesterol synthesis, the LDL receptor up-regulation did not appear to be due to the effects on cholesterol synthesis. The LDL receptor stimulatory activity was sensitive to proteolysis and heat. Its molecular mass was approximately 20 kDa based on gel filtration. Several macrophage secretory proteins were tested in HepG2 cultures for LDL uptake stimulation. Of these, oncostatin M (approximately 18 kDa by gel filtration) gave the strongest response. The rank order for LDL uptake stimulation was oncostatin M much greater than interleukin 6 = interleukin 1 = transforming growth factor-beta 1. A neutralizing antibody directed against oncostatin M inhibited the ability of conditioned media to up-regulate LDL receptors by 85%. Thus, our results indicate that macrophages can secrete several proteins that up-regulate LDL receptors in HepG2 cells and that most of the up-regulatory activity in macrophage conditioned media appears to be due to oncostatin M.
Assuntos
Interleucinas/farmacologia , Fígado/metabolismo , Macrófagos/metabolismo , Peptídeos/farmacologia , Receptores de LDL/efeitos dos fármacos , Fator de Crescimento Transformador beta/farmacologia , Animais , Western Blotting , Células Cultivadas , Colesterol/biossíntese , Citocinas/farmacologia , Eletroforese em Gel de Poliacrilamida , Humanos , Fígado/citologia , Neoplasias Hepáticas Experimentais/metabolismo , Camundongos , Oncostatina M , Receptores de LDL/metabolismo , Células Tumorais Cultivadas , Regulação para CimaRESUMO
Oncostatin M is a growth regulatory protein secreted by macrophages and activated T lymphocytes. In a hepatoma cell line (HepG2) the polypeptide very potently increased low density lipoprotein (LDL) uptake with an EC50 of 0.1-0.2 nM. The stimulation of LDL uptake was detectable by 2 h, was maximal by 8 h, and remained elevated through 20 h of oncostatin M incubation. In a similar fashion, oncostatin M also increased the number of cell surface LDL receptors by a mechanism that was inhibited by cycloheximide or the protein kinase C inhibitor H-7. Oncostatin M stimulation of LDL uptake and receptor protein occurred regardless of the state of cholesterol-dependent regulation of HepG2 LDL receptor (i.e. cells incubated in medium containing lipoproteins responded to the same extent as did cells incubated in the absence of lipoproteins). No significant effects were observed on sterol synthesis over 8 h or on DNA synthesis over 24 h. Oncostatin M induced rapid alterations in HepG2 phospholipid metabolism. Within 5-15 min there was a 20-50% increase in incorporation of 32P into several classes of phospholipids, including the phosphoinositides. Radiolabeled diacylglycerol levels were elevated 20% by 2 min and nearly 50% by 15 min. In addition, the polypeptide induced rapid increased (within 1 min) in phosphorylation of HepG proteins on tyrosine residues. Stimulation of both phosphotyrosine and LDL receptor up-regulation by oncostatin M was decreased by the tyrosine kinase inhibitor genistein. We propose that oncostatin M up-regulates HepG2 LDL receptor expression by a mechanism that includes stimulation of a tyrosine kinase followed by generation of phospholipid-related second messengers.
Assuntos
Carcinoma Hepatocelular/metabolismo , Neoplasias Hepáticas/metabolismo , Peptídeos/farmacologia , Receptores de Citocinas , Receptores de LDL/metabolismo , 1-(5-Isoquinolinasulfonil)-2-Metilpiperazina , Reagentes de Ligações Cruzadas , Cicloeximida/farmacologia , DNA de Neoplasias/biossíntese , Ensaio de Imunoadsorção Enzimática , Humanos , Isoquinolinas/farmacologia , Oncostatina M , Fosforilação , Piperazinas/farmacologia , Receptores de Superfície Celular/metabolismo , Receptores de Oncostatina M , Células Tumorais Cultivadas , Tirosina/metabolismo , Regulação para CimaRESUMO
Analogues of the human erythroid membrane skeletal component protein 4.1 have been identified in perfused rat tissues and human T and B lymphocyte cell lines. olyclonal antibodies were used which are specific for all domains of protein 4.1, the spectrin-actin-promoting 8-Kd peptide, the membrane-binding 30-Kd domain, and the 50-Kd domain. Antibody reactivity, by Western blotting of tissue homogenates, shows reactivity with proteins varying in molecular weight from 175 Kd to 30 Kd. Further, these protein 4.1 analogues appear to be expressed in a tissue-specific fashion. Of the analogues detected there appear to be at least three classes: analogues containing all erythroid protein 4.1 domains, analogues containing all domains but with modified antigenic epitopes, and analogues containing only some domains. Chemical cleavage at cysteine linkages indicates that in analogues containing the 30-Kd region the location of cysteine is highly conserved. This datum suggests that in nonerythroid 4.1 isoforms of higher molecular weight the additional protein mass is added to the amino terminal end (30 Kd end).
Assuntos
Proteínas do Citoesqueleto , Proteínas de Membrana/análise , Neuropeptídeos , Animais , Química Encefálica , Eletroforese em Gel de Poliacrilamida , Humanos , Imunoquímica , Peso Molecular , Especificidade de Órgãos , Glândula Parótida/análise , Ratos , Ratos EndogâmicosRESUMO
We describe an NH4+-specific transport system in the N2-fixing symbiotic actinomycete Frankia sp. strain CpI1. [14C]methylammonium was used as an NH4+ analog. No specific transport process was detected when cells were grown on high concentrations of NH4+. A transport system with a high affinity for CH3NH3+ was synthesized after 3 to 4 h of nitrogen starvation. Methylammonium transport was not significantly inhibited by a variety of amino acids, primary amines, and polyamines. Ammonium completely eliminated CH3NH3+ transport. The Km for CH3NH3+ transport was around 2 +/- 1.8 microM with a Vmax of 4 to 5 nmol/min per mg of protein. The electron transport inhibitors cyanide and azide eliminated uptake, as did the uncoupler carbonyl cyanide-m-chlorophenylhydrazone. The sulfydryl reagent p-chloromercuribenzoic acid and the heavy metal thallium also inhibited uptake, suggesting the presence of an NH4+-specific permease. Concentration of CH3NH3+ across the membrane was demonstrated by conducting uptakes at low temperature to slow the metabolism of CH3NH3+ by glutamine synthetase. At 7 degrees C most of the label was concentrated inside the cells in a form that could be chased from the cells by adding excess NH4+ to the medium. At 30 degrees C most of the label was present as an impermeant metabolite. Thin-layer chromatography of cell extracts confirmed that the radioactivity inside the cells was mainly in the form of CH3NH3+ at 7 degrees C but was present as an unidentified metabolite at 30 degrees C. These studies demonstrate that Frankia sp. strain CpI1 has a high-affinity NH4+ transport system that is synthesized in response to NH4+ starvation.