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1.
Arthur H. L. From Dwight S. Fullerton Khalil Ahmed 《Molecular and cellular biochemistry》1990,94(2):157-165
The structure-activity relationships of the genin moieties of digitalis glycosides are commonly elucidated by determining the inhibitory potency of a variety of genins toward the plasma membrane Na+, K+-ATPase; qualitatively these relationships appear to be fairly independent of the specific Na+, K+-ATPase preparation utilized for the analysis. To determine whether this is the case with regard to the sugar moieties of glycosides, the inhibitory effects of 12 monoglycosides of digitoxigenin toward four Na+, K+-ATPase preparations of different origin were measured. It was found that while recognition of the major structural determinants of sugar activity appeared to be independent of enzyme source, recognition of the minor structural determinants of activity showed some source dependence. It was also observed that the intrinsic sensitivity to sugar potentiation may be source dependent and unrelated to intrinsic sensitivity to inhibition by digitoxigenin. These observations are compatible with a model of the Na+, K+-ATPase sugar binding site(s) in which intrinsic sensitivity to sugar attachment as well as recognition characteristics (for sugar structural features) both determine the extent to which a sugar moiety may contribute to the activity of monoglycosides. Further, in these studies one of the Na+, K+-ATPase preparations employed was obtained from rat brain, a tissue known to contain a mixture of ouabain sensitive and insensitive isoforms. We have observed that the rigorous purification techniques employed appear to have selectively removed from or denatured the less ouabain sensitive al isoform found in this enzyme preparation. 相似文献
2.
Antigenic relatedness between human lecithin-cholesterol acyltransferase and phospholipases of the A2 family 总被引:1,自引:0,他引:1
A monoclonal antibody, B10, generated against pure human lecithin-cholesterol acyltransferase (EC 2.3.1.43) caused the inhibition of the esterolytic and cholesterol esterifying activities of the enzyme. This antibody also reacted with a number of pancreatic and snake venom phospholipases A2 species but not phospholipase A1. A concentration-dependent inhibition of phospholipase A2 was also seen in the presence of B10. Treatment of lecithin-cholesterol acyltransferase or B10-reacting phospholipases with phenacyl bromide, a reagent known to interact with the active site of phospholipase A2, inhibited both their esterolytic activity and their capacity to bind to B10. A dimeric phospholipase A2 species with a known occluded active site did not cross-react with B10. Thus, lecithin-cholesterol acyltransferase and some enzymes of the phospholipase A2 family share a common antigenic determinant which is probably located near or at their esterolytic active site. 相似文献
3.
2419 freshwater fishes from the Sudan were examined for helminth parasites and found to harbour one monogenean species, 15 species of adult digenetic trematodes, three species of larval trematodes, 16 species of adult cestodes, 13 species of adult nematodes, two species of larval nematodes and three species of acanthocephalans. Four species of adults and four species of larval worms are recorded for the first time in the Sudan and 30 new hosts are listed. The intensity of infestation of each species, the host-specificity and the variations in the infestation of fishes are discussed. The helminth fauna of the Sudan is compared with that of other African countries. 相似文献
4.
5.
El-Temtamy S. A. Khalil S. A. Nour-El-Din A. A. Gaber A. 《Applied microbiology and biotechnology》1984,19(6):376-381
Summary Liquid-phase volumetric oxygen transfer coefficients were evaluated in a bubble column containing yeast suspensions, using the instationary oxygen absorption method and a polarographic oxygen electrode. The electrode time lag was found to be independent of both the system studied and the operating conditions. The volumetric oxygen mass transfer coefficients k
L
a could be reasonably predicted by calculating k
L from the equation derived by Bhavaraju et al. or the empirical equation of Calderbank and Moo-Young and a from the experimental gas hold-up values.Nomenclature
a
Exponent in Eq.6 or specific gas-liquid interfacial area based on reactor volume m
-
b
Exponent in Eq. 6
-
C
Constant in Eq 6 or oxygen concentration in the liquid phase g/ml
-
C
*
Equilibrium oxygen concentration g/ml
-
C
0
Oxygen concentration in the liquid phase at t=0 g/ml
-
C
E
Oxygen concentration as determined by the polarographic electrode g/ml
-
D
B
Bubble equivalent diameter mm
-
D
l
Oxygen diffusivity in the liquid phase m2/s
-
g
Acceleration of gravity m/s2
-
K
Consistency index Pasn
-
K
L
Liquid-phase mass transfer coefficient m/s
-
n
Power law exponent
-
Pe
sw
Peclet number based on bubble swarm velocity
-
S
C
Schmidt number
-
Sh
Sherwood number
-
i
Time s
-
U
B
Bubble rise velocity in infinite medium m/s
-
U
g
Superficial air velocity based on column cross-sectional area m/s
-
U
sw
Bubble swarm velocity defined by Eq.15 m/s
-
Y
MSW
Mass transfer coeficient correction factor for mobile interfaces in pseudo-plastic fluids Eq. 7
-
Y
MSW
Mass transfer coefficient correction factor for immobile interface in pseudo-plastic fluids Eq. 8
Greek letters
l
Density of liquid g/ml
- sus
Density of unaerated suspension g/ml
- wet cell
Density of yeast wet cells g/ml
-
l
Viscosity of the liquid Pas
- app
Apparent viscosity of power law fluid Pas
-
E
Electrode time lag s
-
l
Time lag due to resistance of the gas-liquid interface
s
-
g
Gas hold-up, volume fraction occupied by the gas phase
-
l
Liquid hold-up
-
c
Wet cell volume fraction 相似文献
6.
The Nile catfish, Clarias lazera was found to concentrate radioactive cesium-134 and cobalt-6o from the aquatic environment. For cesium-134 the rate of uptake increased by increase of exposure time, while for cobalt-6o maximum uptake occurred after one day of exposure. The corresponding concentration factors at maximum uptake levels were 0.37 and 0.36 for cesium and cobalt respectively.The internal distribution of these radionuclides in the different tissues and organs of the fish due to uptake from the aquatic environment followed the decreasing order:For 134Cs: muscle, bone, gills, stomach, kidneys, intestine and liver.For 60Co: bone, muscle, gills, intestine, kidneys, stomach and liver.The internal distribution due to ingestion of these radionuclides followed nearly the same order as was found in case of uptake from the aquatic environment. 相似文献
7.
In the infested skin of tick-resistant guinea pigs, indirect immunofluorescence techniques have revealed that antigens from the ticks' salivary glands are associated with discrete dendritic cells in the epidermis. Evidence is presented to support the suggestion that these antigen-retaining cells are Langerhans cells. 相似文献
8.
The sugarbeet cultivar Kaumera was found to be highly susceptible to infection by the root-rot pathogens Rhizoctonia solani and Sclerotium rolfsii in the absence of salinity stress. Under this environmental condition, R. solani was more efficient than S. rolfsii in producing cell wall-degrading enzymes in infected hypocotyls. Xylanase and galactanase were most effective. The rate of cell wall degradation by R. solani was nearly 2.5 times that of S. rolfsii when cells walls of healthy hypocotyls were used as sole carbon substrate for the in vitro produced crude enzymes.Under salinity stress the pathogenicity and the performance of cell wall-degrading enzymes of R. solani and S. rolfsii varied profoundly. Pathogenicity studies showed that R. solani appeared to be more tolerant than S. rolfsii of the salinity stresses applied, and relatively more virulent to cv Kaumera. The activities of cell wall enzymes of R. solani decreased and those of S. rolfsii increased with increased salt concentration when cell wall material was used as a sole carbon source. The metabolic products produced under salinity stress by R. solani and R. solani in the cell wall amended culture media shifted the initial pH towards neutrality or slight alkalinity for R. solani and to high acidity for S. rolfsii.When model substrates were used, xyland and galactan were the most responsive substrates for degradation by the cell wall enzymes of the two fungi studied. The rate of degradation was higher for S. rolfsii than for R. solani. The excessive acidity in salt stressed S. rolfsii culture media suggested reduced activities of the enzymes involved in cell wall degradation in vivo. This may explain the decreased virulence potentialities. 相似文献
9.
Khalil Ahmed Alan T. Davis Said A. Goueli Michael J. Wilson 《Biochemical and biophysical research communications》1980,96(1):326-332
32P-labelled chromatin proteins from rat liver and ventral prostate were fractionated according to the procedure designed to enrich high-mobility-group (HMG) nonhistone proteins. This fraction, however, reproducibly demonstrated small amounts of apparently basic nonhistone proteins other than HMG nonhistone proteins. These proteins appeared to be tissue specific and were highly labelled with 32P. The 32P-labelled phosphoproteins were soluble in trichloroacetic or perchloric acid, migrated in acid-urea polyacrylamide gels, and demonstrated pI values ranging from 6.8 to 7.5. The HMG proteins 1 and 2 showed no incorporation of radioactivity under these experimental conditions. 相似文献
10.
Protein phosphokinase activity of rat liver nuclear membrane 总被引:3,自引:0,他引:3
The presence of protein phosphokinase activity in a purified nuclear-membrane preparation from adult rat liver was demonstrated by measuring the incorporation of 32P from γ-32P-ATP into endogenous nuclear-membrane proteins as well as into the exogenous protein substrates, dephosphophosvitin (DPV) and lysine-rich histone (LRH). The activity of this enzyme toward DPV was 60 times greater than that toward LRH. cAMP and cGMP did not appear to affect the phosphorylation of endogenous-membrane proteins. 相似文献