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41.
Five different clones, homologous to the structural gene for the sweet-tasting plant protein thaumatin, have been isolated from leaf DNA of Thaumatococcus daniellii Benth. Restriction maps, hybridization studies, S1-nuclease mapping and R-loop formation revealed that the thaumatin genes isolated belong to one multigene family, and have two very small introns situated at different positions in the various structural genes. A similar situation prevails in a number of seed storage genes. This suggests a similarity between the sweet-tasting protein thaumatin and seed storage proteins. 相似文献
42.
Alastair A. Macdonald Ben Colenbrander Dirk H. G. Versteeg Alfred Heilhecker Cees J. G. Wensing 《Development genes and evolution》1984,193(1):19-23
Summary Dopamine, norepinephrine and epinephrine were measured by radioenzymatic assay in blood plasma samples drawn from the umbilical arteries of 30 anaesthetised Landrace pig fetuses. Just prior to term, the concentrations of dopamine (0.46±0.14 ng·ml–1) and norepinephrine (1.74±0.60 ng·mg–1) were lower than earlier in gestation, whereas epinephrine concentrations at term (0.80±0.31 ng·ml–1) were similar to those at mid-gestation, intervening stages of gestation having higher levels of plasma epinephrine. Fetal hypoxia was induced by clamping the umbilical cord for 2 min and the catecholamines determined in arterial blood samples immediately thereafter, then again 3 min after removal of the clamp. Inconsistent effects of cord clamping on catecholamine levels were seen at 55 days, but thereafter, in all but one instance, the hormone levels were increased. Fetuses near term tended to respond less than fetuses at 75 and 96 days gestation (term=114±1 day). Catecholamines were also present in the circulation of fetuses decapitated at 42 days gestation and studied at 109±1 days. The average concentrations of dopamine (1.12±0.27 ng·ml–1) and norepinephrine (8.23±3.04 ng·ml–1) were greater than in intact fetuses, the plasma epinephrine levels being comparable to, or slightly higher than, those in intact fetuses. The results demonstrate that catecholamines are present in the circulation of the intact and decapitated pig fetus and that the actual concentrations and the type of response to umbilical cord clamping are dependent on gestation age. 相似文献
43.
Freeze fracturing electron microscopy of Escherichia coli K12 cells showed that the outer fracture face of the outer membrane is densily occupied with particles. On the inner fracture face of the outer membrane, pits are visible, which are probably complementary to the particles at opposite fracture face. This observation suggests that the particles are micelle-like. In some mutants which lack one or more major outer membrane proteins the density of particles is reduced. The loss of protein d appeared to a prerequisite for this phenomenon. However, mutants which lack all glucose and heptose-bound phosphate in their lipopolysaccharide also have a reduction in particle density whereas, the amount of protein d is normal. Moreover, loss of lipopolysaccharide by EDTA treatment also caused a reduction in the density of particles. From these results it is hypothesized that the particles consist of lipopolysaccharide aggregates stabilized by divalent cations and probably complexed with protein and/or phospholipid. 相似文献
44.
Retinoic acid induces transglutaminase activity but inhibits cornification of cultured epidermal cells 总被引:4,自引:0,他引:4
In cultured mouse epidermal basal cells, retinoic acid is a potent inducer of transglutaminase, the enzyme responsible for isodipeptide bond formation in protein cross-linking in the production of the cornified membrane during terminal differentiation. Paradoxically retinoic acid also inhibits the formation of the cross-linked envelope and greatly reduces the level of dipeptide bond formation in epidermal cells induced to differentiate by calcium. These results suggest a novel mechanism by which retinoids can modify transglutaminase activity and epidermal differentiation. 相似文献
45.
46.
M C Apella S N González M E Nader de Macías N Romero G Oliver 《The Journal of applied bacteriology》1992,73(6):480-483
The inhibitory effect of lactobacilli on growth of Shigella sonnei was studied. The effect was not due to pH alone, as addition of hydrochloric, lactic or acetic acids to culture media did not inhibit the normal growth of the shigellas. The degree of inhibition was measured by disc assay and showed that the inhibitory substance(s) can be extracellular and diffusible, varying the degrees of inhibition depending on the media tested. When broth was inoculated with mixed cultures of Lactobacillus and Shigella strains, the inhibition began at 6 h and the death phase at 9 h. The higher inhibition was produced by the mixture of lactobacilli (35.5 +/- 2.5% at 6 h culture, 57.4 +/- 1.9% at 9 h and 91.2 +/- 1.2% at 14 h). The degree of inhibition was higher when the relationship pathogen : lactobacilli was 1:10(3). The specific growth rate of lactobacilli and shigella was different in pure or mixed cultures. When the lactobacillus alone was grown for 12 h and the shigellas then added, the numbers of shigellas began to decrease immediately at 37 degrees C. This work shows that the Lactobacillus strains employed in fermented milk can be used to inhibit the growth of Sh. sonnei. 相似文献
47.
Use of Bioluminescence Markers To Detect Pseudomonas spp. in the Rhizosphere 总被引:12,自引:7,他引:5 下载免费PDF全文
Letty A. de Weger Paul Dunbar Walter F. Mahafee Ben J. J. Lugtenberg Gary S. Sayler 《Applied microbiology》1991,57(12):3641-3644
The use of bioluminescence as a sensitive marker for detection of Pseudomonas spp. in the rhizosphere was investigated. Continuous expression of the luxCDABE genes, required for bioluminescence, was not detectable in the rhizosphere. However, when either a naphthalene-inducible luxCDABE construct or a constitutive luxAB construct (coding only for the luciferase) was introduced into the Pseudomonas cells, light emission could be initiated just prior to measurement by the addition of naphthalene or the substrate for luciferase, n-decyl aldehyde, respectively. These Pseudomonas cells could successfully be detected in the rhizosphere by using autophotography or optical fiber light measurement techniques. Detection required the presence of 103 to 104 CFU/cm of root, showing that the bioluminescence technique is at least 1,000-fold more sensitive than β-galactosidase-based systems. 相似文献
48.
H B Nader M A Porcionatto I L Tersariol M A Pinhal F W Oliveira C T Moraes C P Dietrich 《The Journal of biological chemistry》1990,265(28):16807-16813
The purification of two heparitinases and a heparinase, in high yields from Flavobacterium heparinum was achieved by a combination of molecular sieving and cation-exchange chromatography. Heparinase acts upon N-sulfated glucosaminido-L-iduronic acid linkages of heparin. Substitution of N-sulfate by N-acetyl groups renders the heparin molecule resistant to degradation by the enzyme. Heparitinase I acts on N-acetylated or N-sulfated glucosaminido-glucuronic acid linkages of the heparan sulfate. Sulfate groups at the 6-position of the glucosamine moiety of the heparan sulfate chains seem to be impeditive for heparitinase I action. Heparitinase II acts upon heparan sulfate producing disulfated, N-sulfated and N-acetylated-6-sulfated disaccharides, and small amounts of N-acetylated disaccharide. These and other results suggest that heparitinase II acts preferentially upon N,6-sulfated glucosaminido-glucuronic acid linkages. The total degradation of heparan sulfate is only achieved by the combined action of both heparitinases. The 13C NMR spectra of the disaccharides formed from heparan sulfate and a heparin oligosaccharide formed by the action of the heparitinases are in accordance to the proposed mode of action of the enzymes. Comparative studies of the enzymes with the commercially available heparinase and heparitinase are described. 相似文献
49.
Release of Rhizobium spp. from Tropical Soils and Recovery for Immunofluorescence Enumeration 总被引:13,自引:13,他引:0 下载免费PDF全文
Limitations associated with immunofluorescence enumeration of bacteria in soil derive largely from the efficiency with which cells can be separated from soil particles and collected on membrane filters for staining. Many tropical soils fix added bacteria tightly, resulting in low recoveries. Eight soils, representative of three of the major soil orders found in the tropics (oxisols, vertisols, and inceptisols), were tested for recovery of added Rhizobium strains. All except one Hawaiian andept (Typic Eutrandept) yielded recoveries ranging from <1 to 13%. Recovery from the andept was 100%. In soil-sand mixtures, addition of only a small amount of soil caused a dramatic decrease in recovery of added rhizobia. Increasing the soil content of the mixture from 0% (10 g of sand) to 50% (5 g of soil-5 g of sand) reduced recoveries from >90 to <1%. Varying the ionic strength and pH of the extracting solution did not cause marked increases in recovery. Protein solutions, ethylenediaminetetraacetate, and NaHCO3, on the other hand, improved release of bacteria. We report a modification to the usual membrane filter immunofluorescence procedure which yielded consistently high and reproducible recovery (coefficient of variation, 30%) of rhizobia from several tropical soils. In the modified procedure, partially hydrolyzed gelatin, diluted in ammonium phosphate, was used to suspend the soil. This caused dispersion of the soil and release of the bacteria from soil flocs. The efficiency of recovery of Rhizobium spp. from several tropical and two temperate soils remained high as the content of these soils in soil-sand mixtures was increased from 0 to 100%. The modified membrane filter immunofluorescence procedure was used to follow the growth of a strain of chickpea (Cicer arietinum) Rhizobium in a sterilized oxisol. The results showed a close agreement with viable counts at different stages during the growth cycle. Diluent for the hydrolyzed gelatin also had a marked effect on recovery. The efficiency of release of Rhizobium spp. from an oxisol was in the following order for the diluents used: 0.1 M (NH4)2HPO4 > 0.1 M Na2HPO4 = 0.1 M sodium-phosphate-buffered saline (pH 7.2) > 0.2 M NH4Cl > 0.2 KCl > NaCl = LiCl > water. 相似文献
50.
Rat bone marrow microsomal heme oxygenase activity has been studied and optimal condition for the measurement of this activity are described. The activity of bone marrow heme oxygenase was linear with time and protein concentration as measured under these assay conditions. Bilirubin formation by the heme oxygenase complex system was observed with either a NADPH generating system or with NADH as electron donor. The enzyme activity for heme degradation supported by NADH proceeds at a comparable rate to that observed with NADPH as reducing equivalent. It thus appears that this oxidation reaction must be more complex than simply involving NADPH as the sole election donor as has been previously proposed. 相似文献