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751.
752.
Two synthetic approaches leading toN-4-carboxymethyl-2-nitrobenzyloxycarbonyl derivatives of model compounds and of glycosylsphingosines are described. The carboxymethyl group can be converted into a hydrazido derivative and the resulting products react with an active ester polymer yielding light-sensitive polymeric products that may subsequently serve as acceptors in glycosyltransferase reactions.Author for correspondence. Address until September 1990; Graduate Department of Biochemistry, Brandeis University, 415 South Street, Waltham, MA 02254, USA 相似文献
753.
Uri Liberman 《Theoretical population biology》1976,10(2):127-132
The evolutionary fate of rare modifiers, based on the modifier theory of meiotic drive, is studied in this paper. It is shown that a polymorphism based on Mendelian segregation is never stable for any recombination frequencies between 0 and , and that, for tight linkage between the main locus and the modifier locus, the modifier locus tends towards heterozygosity. 相似文献
754.
Elevated CO2 stimulates plant growth and affects quantity and composition of root exudates, followed by response of its microbiome. Three scenarios representing nitrate fertilization regimes: limited (30 ppm), moderate (70 ppm) and excess nitrate (100 ppm) were compared under ambient and elevated CO2 (eCO2, 850 ppm) to elucidate their combined effects on root-surface-associated bacterial community abundance, structure and function. Wheat root-surface-associated microbiome structure and function, as well as soil and plant properties, were highly influenced by interactions between CO2 and nitrate levels. Relative abundance of total bacteria per plant increased at eCO2 under excess nitrate. Elevated CO2 significantly influenced the abundance of genes encoding enzymes, transporters and secretion systems. Proteobacteria, the largest taxonomic group in wheat roots (~ 75%), is the most influenced group by eCO2 under all nitrate levels. Rhizobiales, Burkholderiales and Pseudomonadales are responsible for most of these functional changes. A correlation was observed among the five gene-groups whose abundance was significantly changed (secretion systems, particularly type VI secretion system, biofilm formation, pyruvate, fructose and mannose metabolism). These changes in bacterial abundance and gene functions may be the result of alteration in root exudation at eCO2, leading to changes in bacteria colonization patterns and influencing their fitness and proliferation.Subject terms: Microbiome, Microbial ecology, Metagenomics, Microbial ecology 相似文献
755.
The watersweet aftertaste produced in humans in responseto tasting intensive sweeteners such as neohesperidin dihydrochalconeand thaumatin was studied. This watersweet aftertasteincreased with sweetener concentration and diminished with time.The decay in the sweet intensitytime relationships fitteda negative exponential function in a pattern similar to thatwhich occurs when other methods for determining persistenceare employed. Persistence time contants (T) were dependent uponthe maximal perceived sweet intensity (Ip-max) observed at theinitial time of tasting. The use of this procedure is proposedfor determining persistence of intensive sweeteners under circumstanceswhere controlled pH and temperature are desired. 相似文献
756.
Burkholderia cepacia is an opportunistic pathogen that causes serious pulmonary infections in cystic fibrosis patients. We have purified and partially
characterized one potential virulence factor for the organism—a nonhemolytic phospholipase C—and we studied the effect of
iron restriction and choline and phosphate concentrations on the expression of phospholipase C. Iron limitation did not affect
expression, the effect of choline was variable, and high phosphate concentrations repressed expression. Experiments with heat-treated
spent culture supernatants suggested that autoinducers affected the expression of the phospholipase and two other potential
virulence factors, a protease and a lipase. We screened 26 B. cepacia isolates for autoinducer activity: 11 induced violacein production in the autoinducer-deficient mutant Chromobacterium violaceum CV026. Spent supernatants from two strains, one that was positive in the C. violaceum assay and one that was negative, were tested for inducing early expression of phospholipase C, protease, and lipase in homologous
and heterologous cultures. Expression of all three enzymes was increased or induced at an earlier stage in the growth curve
in every case, suggesting not only that autoinducers were involved in the regulation of the expression of these enzymes, but
also that the autoinducers were of two different classes.
Received: 13 May 1999 / Accepted: 14 June 1999 相似文献
757.
Naim Michael; Dukan Emmanuel; Yaron Lyat; Levinson Martha; Zehavi Uri 《Chemical senses》1986,11(4):471-483
The maximal perceived sweet intensity (Ipmax) and the sweetpersistence constant (T) of neohesperidin dihydrochalcone (NHD),were significantly reduced in a mixture containing naringin(NAR), a bitter flavone analog of NHD Sucrose octa-acetate (SOA),another bitter stimulus, reduced the Ipmax of NHD in mixtures,but no appreciable decrease in T values was found. Linear regressionanalyses performed on the IPmax data of either NHD + NAR orNHD + SOA (logIpmax versus log concentration) produced slopevalues lower than those of NHD alone. Moreover, taste similarityexperiments revealed that the mixture of NHD + NAR was locatedfurther than NHD from the sugar area in the multi-dimensionalscaling (MDS) map. It is concluded that the reduction in Tvaluesof NHD by NAR was apparently related to the reduced Ipmax levelsand that such a mixture produces a sweet quality inferior tothat of NHD. 相似文献
758.
Eliahu Stoupel Eugeny Abramson Jaqueline Sulkes Joseph Martfel Nechama Stein Meir Handelman Michael Shimshoni Pnina Zadka Uri Gabbay 《International journal of biometeorology》1995,38(4):199-203
In recent years, the possible association of changes in mortality from cardiovascular disease and myocardial infarction (MI) and deaths related to violence and the suicide rate has been repeatedly discussed. This study examined the relationship between cosmic physical changes (solar, geomagnetic and other space activity parameters) and changes in the total number of in-hospital and MI-related deaths and deaths from suicide to determine if a relationship exists between the distribution of total and MI-related deaths with suicide over time; some differences in the serotonergic mechanisms involved in the pathogenesis of MI and suicide were also taken into account. All suicides (n=2359) registered in the State of Israel from 1981 to 1989 (108 months) were analysed and compared with the total number of deaths (n=15601) and deaths from MI (n=1573) in a large university hospital over 180 months (1974–1989). The following were the main features of the Results. (1) Monthly suicide rate was correlated with space proton flux (r=0.42,P=0.0001) and with geomagnetic activity (r=–0.22,P=0.03). (2) Total hospital and MI-related deaths were correlated with solar activity parameters (r=0.35,P<0.001) and radiowave propagation (r=0.52-0.44,P<0.001), an with proton flux (r=–0.3 to –0.26,P<0.01). (3) Monthly suicide distribution over 108 months was correlated with MI (r=–0.33,P=0.0005) and total hospital mortality (r=–0.22,P=0.024). (4) Gender differences were prominent. We conclude that the monthly distributions of suicides and deaths from MI are adversely related to many environmental physical parameters and negatively correlated with each other. 相似文献
759.
Uri Gerson 《BioControl》1968,13(2):163-173
Résumé La biologie des aphelinidesAphytis hispanicus (Mercet) etProspaltella inquirenda
Silvestri, respectivement ecto et endoparasite deParlatoria pergandii
Comstock, a été étudiée comparativement en laboratoire.A. hispanicus accomplit son cycle en 34 jours environ à 20 °C et en 16 jours à 28 °C; il produit en moyenne 23,8 descendants, tandis que
pourP. inquirenda ces durées sont de 62 et 26 jours et le nombre moyen de descendants 20,6. Le comportement pendant l'oviposition et les interactions
diverses entre l'h?te et le parasite ont été notés. Le nectar d'agrumes a prolongé la vie des deux parasites autant que le
miel.A. hispanicus a généralement une vie plus prolongée queP. inquirenda. Le premier parasite a mieux survécu dans des conditions de forte humidité relative (61%, 80%), maisP. inquirenda s'est trouvé favorisé dans des conditions de faible humidité relative, ainsi qu'après une exposition à des températures extrêmes.
En conclusion,A. hispanicus a un taux plus rapide de croissance, tandis queP. inquirenda est mieux adapté aux conditions naturelles.
This research has been finaneed in part by Grant No. FG-Is-227 made by the United States Department of Agriculture under P.L. 480. 相似文献
This research has been finaneed in part by Grant No. FG-Is-227 made by the United States Department of Agriculture under P.L. 480. 相似文献
760.
The isoelectrofocusing patterns of
-amino acid oxidase (LAO) from venom gland homogenates and of the secreted venom of Vipera palaestinae have been compared. The LAO isozyme profile of actively synthesizing gland spans over a wider range of pIs (4.8–6.0) and includes more variants as compared with the profile of the secreted venom. A basic shift of the isoelectrofocusing pattern of LAO obtained by treatment of the gland homogenate or the venom with neuraminidase indicates that sialic acid residues are responsible for the changes in the electronegativity of the isozymes. Analyses of subcellular fractions show that the microsomal fraction of the venom gland homogenate exhibits the highest multiplicity of molecular forms of LAO, whereas the fraction including the secretory granules has an isozyme profile similar to the venom. Double labelling experiments show that the newly synthesized LAO include isozymes which span over a wide range of pIs, whereas later on labelling of the more acidic isozymes is prominent. The results obtained may suggest that the sialic acid residues which are attached to LAO during its transport serve as “markers” for secretion. 相似文献