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1.
The soilborne rhizosphere-competent fungal biocontrol agent Trichoderma harzianum isolate Th008 secreted trichodermin (MW = 292) and a small peptide (MW = 876) in culture. These compounds were antagonistic in culture to the mycelial growth of the soilborne fungal pathogen Rhizoctonia solani isolate 2B-12, which is highly virulent to soybean ( Glycine max )seedlings. When 100mg of dried autoclaved mycelial mat of R. solani was added to 200 ml liquid cultures of T. harzianum , the quantity of antimycotic compounds secreted by the latter was 3.5 times greater than that of the antagonist alone. R. solani secreted a coumarin derivative (MW = 313) in liquid culture, which inhibited the mycelial growth of T. harzianum ; however, inhibition of the growth of the antagonist required a greater concentration than that for the antimycotic compounds produced by the antagonist against the pathogen. The inclusion of 100 mg of dried autoclaved mycelial mat of T. harzianum in a 200 ml liquid culture of R. solani did not affect the quantity of the antimycotic compound produced by the pathogen.  相似文献   
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One hundred and ninety eight men seropositive for human immunodeficiency virus (HIV) antibody and 58 HIV antibody seroconverters were studied for an average of 19.3 (SEM 0.5) months to assess the relation between HIV antigenaemia and the risk of developing the acquired immune deficiency syndrome (AIDS) and AIDS related complex. Forty (20.2%) of the 198 HIV antibody seropositive men were antigen positive at entry and remained so during follow up. Eight (13.8%) of the 58 HIV antibody seroconverters and 20 (12.7%) of the remaining 158 HIV antibody seropositive men became antigen positive during follow up, resulting in an end point attack rate for HIV antigenaemia of 14.3%. AIDS related complex was diagnosed in 25 (15.8%) of the HIV antigen negative men and in 14 (20.7%) of the HIV antigen positive men. AIDS was diagnosed in 15 men, resulting in an end point attack rate for AIDS of 23.9% in the HIV antigen positive group and 1.3% in the antigen negative group. HIV antibody seropositive men without symptoms but with persistent HIV antigenaemia are at increased risk of developing AIDS and AIDS related complex.  相似文献   
4.
Hemorrhage in mice produces alterations in B cell repertoires   总被引:1,自引:0,他引:1  
Multiple organ system failure secondary to infection is the major cause of late deaths after trauma and hemorrhage. The production by B cells of antibodies directed against bacterial antigens is an important component of host defenses. In order to determine the effects of hemorrhage on B cell function, we examined hemorrhage-induced alterations in available (clonal precursors) and actual (plasma cells) B cell repertoires in the course of an immune response toward bacterial antigens. Hemorrhage produced greater than twofold decreases in the absolute frequency and number of clonal precursors specific for the bacterial antigens dextran, levan, and pneumococcal polysaccharide type II. After blood loss, there were decreases in absolute frequency, but not in numbers, of clonal precursors capable of producing antibodies against the nonbacterial antigens ovalbumin and mouse transferrin. Immunization with the bacterial antigen levan within 24 hr of hemorrhage resulted in approximately 50% fewer levan-specific plasma cells than that seen in normal, unhemorrhaged mice. These results demonstrate that hemorrhage produces marked alterations in B cell repertoires, which may contribute to postinjury abnormalities in host defenses.  相似文献   
5.
β-thalassemia mutations in the Portuguese population   总被引:2,自引:0,他引:2  
Summary In this study we have carried out haplotype analysis on the -globin gene cluster and characterized the -thalassemia mutation by oligonucleotide hybridization in 14 patients with thalassemia major and 5 with sickle cell/-thalassemia originating from southern Portugal. We found that three mutations, namely the °-39, ° IVS-1 nt 1 and + IVS-1 nt 110 are prevalent accounting for 53%, 32% and 10% of the -thalassemia chromosomes respectively. In general each mutation was associated with a specific chromosomal haplotype; the ° mutation, however, was linked to three different haplotypes. These results indicate that three oligo-probes complementary to the most common mutations allow prenatal diagnosis by oligonucleotide analysis in 96% of the couples at risk of having offspring with thalassemia major in southern Portugal.  相似文献   
6.
The lymphocyte composition of spleen, lymph nodes, bone marrow, and thymus of mice submitted to hydroxyurea treatments for four consecutive days was studied. The treatment selects for small lymphocyte populations that represent between 4 and 20% of control numbers in the various organs. Spleen and bone marrow contain the same B cell population with a low IgM, high IgD, low I-E phenotype, which respond to LPS at control clonal frequencies. The T cell compartment is equally depleted, and the lymphocytes remaining contain frequencies of clonable cells in response to mitogens and IL-2 that are comparable to those detected in normal spleen cells. Overall, the results suggest that only a minor fraction of all lymphocytes in a normal young adult mouse have life spans longer than 4 days.  相似文献   
7.
Pyrophosphate-dependent phosphofructokinase (PPi-PFK) was purified from the mung bean Phaseolus aureus. The enzyme is activated by fructose 2,6-bisphosphate at nanomolar concentrations. The enzyme exhibits Michaelis-Menten kinetics, and the reaction mechanism, deduced from initial velocity studies in the absence of inhibitors as well as product and dead-end inhibition studies, is rapid equilibrium random in the presence and absence of fructose 2,6-bisphosphate. In the direction of fructose 6-phosphate phosphorylation, saturating fructose 2,6-bisphosphate (1 microM) increases V congruent to 9-fold and increases V/KMgPPi and V/KF6P about 30-fold. In the reverse direction (phosphate phosphorylation), the same concentration of activator has little if any effect on V or the Km for inorganic phosphate (Pi) and Mg2+ but does increase V/KFBP about 42-fold. No changes were observed in any of the other rate constants. The binding affinity of fructose 2,6-bisphosphate to all enzyme forms is identical. The activator site of the mung bean PPi-PFK binds fructose 2,6-bisphosphate with a Kact of 30 nM with the 2,5-anhydro-D-glucitol 1,6-bisphosphate (the most effective analogue) 33-fold less tightly. Of the alkanediol bisphosphate series, 1,4-butanediol bisphosphate exhibited the tightest binding (Kact congruent to 3 microM). These and a series of other activating analogues are discussed in relation to the activator site.  相似文献   
8.
Pyrophosphate-dependent phosphofructokinase from the facultative anaerobic bacterium Propionibacterium freudenreichii and from the mung bean Phaseolus aureus has been purified to homogeneity. Potential utilization of carbohydrate substrate analogues for each enzyme was initially screened by using Fourier transform 31P NMR at pH 8 and 25 degrees C and monitoring the appearance of the phosphate resonance in the direction of D-fructose 6-phosphate phosphorylation (forward reaction direction) and, with the bisphosphate analogues, the appearance of the pyrophosphate resonance in the direction of phosphate phosphorylation (reverse reaction direction). Both enzymes are strict in their requirements for the sugar phosphate substrate, with only D-fructose 6-phosphate, D-sedoheptulose 7-phosphate, and 2,5-anhydro-D-mannitol 6-phosphate, or their respective bisphosphates in the reverse reaction direction, utilized as substrates at detectable levels. The dissociation constants for D-psicose 6-phosphate, D-tagatose 6-phosphate, and L-sorbose 6-phosphate are an order of magnitude larger than that for D-fructose 6-phosphate, indicating a stringent steric requirement for the D-threo (trans) configuration at the two nonanomeric furan ring hydroxyl groups. These results strongly suggest that the anomeric, epimeric, and tautomeric form of the sugar phosphate substrates favored by both enzymes is the beta-D-fructofuranose form. Dissociation constants for nonsubstrate analogues were used to provide information on the nature of the active site. Competitive inhibition patterns vs. fructose 1,6-bisphosphate were obtained for a series of 1,n-alkanediol bisphosphates (where n = 2-9).(ABSTRACT TRUNCATED AT 250 WORDS)  相似文献   
9.
Two major classes of mitogen-reactive B lymphocytes defined by life span   总被引:3,自引:0,他引:3  
The relative numbers of short- and long-lived mitogen-reactive B cells in the peripheral pool were evaluated by studying the decay of lipopolysaccharide (LPS)-reactive B lymphocytes in LPS nonresponder, histocompatible hosts for periods of up to 3 wk after cell transfer. The results obtained demonstrate the existence of two major classes of mitogen-reactive B cells defined by life span. The "short-lived" cell component comprises about 80 to 90% of the reactive cells and decays with a life expectancy of 18 to 24 hr. The long-lived cell component, with life expectancies of 10 to 20 days, comprises about 10 to 20% of the reactive cells and is preferentially enriched in circulating B cells. The present ratio for short- and long-lived B cells implies a highly dynamic state for the immune system which must be advantageous in the selection of available repertoires.  相似文献   
10.
Life span of B lymphocytes: the experimental basis for conflicting results   总被引:6,自引:0,他引:6  
Recent claims have challenged the view that most peripheral, mature B cells are long-lived, and propose rates of peripheral decay that are compatible with bone marrow production. This disagreement can only reflect differences in the protocols and methods used to measure peripheral lymphocyte life spans. We have now assessed toxic or other nonselective effects of hydroxyurea treatment on the survival and migration of peripheral, noncycling cells, as well as possible reasons for exaggerated decays of LPS-reactive B cells transferred to LPS nonresponder hosts, the two methods leading to conclusions of short life spans. We also studied general effects on cell survival introduced by either repeated [3H]thymidine injections or the stress associated with surgery, thoracic duct cannulation in particular--methods with which the notion of long life spans had been established. The results failed to show toxic or nonselective effects of hydroxyurea treatments and artificial decays of LPS-reactive cells in adoptive hosts. In contrast, the present experiments demonstrate that both the stress associated with surgery and repeated [3H] thymidine administration profoundly deplete a pool of short-lived B cells, consequently selecting for an apparent higher proportion of long-lived cells.  相似文献   
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