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61.
Nadim Cortas May Arnaout John Salon I. S. Edelman 《The Journal of membrane biology》1989,108(2):187-195
Summary To characterize the molecular properties conveyed by the isoforms of the subunit of Na,K-ATPase, the two major transepithelial transporting organs in the brine shrimp (Artemia salina), the salt glands and intestines, were isolated in pure form. The isoforms were quantified by ATP-sensitive fluorescein isothiocyanate (FITC) labeling. The salt gland enzyme exhibits only the 1 isoform, whereas the intestinal enzyme exhibits both the 1 and the 2 isoforms. After 32 hours of development, Na,K-ATPase activity [in mol Pi/mg protein/hr (1u)] in whole homogenates was 32±6 in the salt glands and 12±3 in the intestinal preparations (mean±sem). The apparent half-maximal activation constants (K
1/2) of the salt gland enzyme as compared to the intestinal enzyme were 3.7±0.6mm
vs. 23.5±4mm (P<0.01) for Na+, 16.6±2.2mm
vs. 8.29±1.5mm for K+ (P<0.01), and 0.87±0.8mm
vs. 0.79±1.1mm for ATP (NS). The apparentK
i's for ouabain inhibition were 1.1×10–4
m
vs. 2×10–5
m, respectively. Treatment of whole homogenates with deoxycholic acid (DOC) produced a maximal Na,K-ATPase activation of 46% in the salt gland as compared to 23% in the intestinal enzyme. Similar differences were found with sodium dodecyl sulfate (SDS). The two distinct forms of Na,K-ATPase isolated from the brine shrimp differed markedly in three kinetic parameters as well as in detergent sensitivity. The differences inK
1/2 for Na+ and K+ are more marked than those reported for the mammalian Na,K-ATPase isoforms. These differences may be attributed to the relative abundances of the subunit isoforms; other potential determinants (e.g. differences in membrane lipids), however, have not been investigated.During the tenure of an Educational Commission For Foreign Medical Graduates Visiting Associate Professorship. 相似文献
62.
作者采用简单的螺胚生长抑制法,证明软体动物细胞具有DNA复制后修复功能,并受咖啡碱抑制。在没有其他诱变剂的参与下,咖啡碱并不损伤DNA,但也没有保护作用。 相似文献
63.
The control of incompatibility in distylous Pulmonaria affinis Jordan (Boraginaceae) 总被引:1,自引:0,他引:1
A.J. RICHARDS JEAN MITCHELL 《Botanical journal of the Linnean Society. Linnean Society of London》1990,104(4):369-380
In P. affinis, pin pollen is shorter on average than thrum pollen. Pins have more coronal hooks on stigmatic papillae than thrums, but gaps between papillae are relatively smaller for thrums. Pin stigmas receive more pollen than thrum stigmas. Thrum stigmas receive more (dissortive) pin pollen, but pin stigmas are assortively pollinated. Pollen only germinates when trapped below papilla coronas. On thrum stigmas, most trapped pollen is pin. Pollen germination is better on thrum stigmas than pin stigmas, and thrum stigmas show a close relationship between numbers of legitimate pollen grains, numbers of germinating grains, and numbers of pollen tubes in the style. There is no inhibition of illegitimate pollen germination. Illegitimate pollen tubes are inhibited in the style. Incompatibility operates by a combination of dissortive pollination, dissortive pollen trapping, and stylar pollen tube inhibition. All heteromorphic features differing between pins and thrums are implicated in the inhibition of within-morph fertilization in thrums. 相似文献
64.
Three post-emergence herbicides (2,4-D, picloram and glyphosate) were applied to samples of an Alberta agricultural soil at
concentrations of 0, 2, 20, and 200 μg g−1. The effects of these chemicals on certain microbial variables was monitored over 27 days. All herbicides caused enhancement
of basal respiration but only for 9 days following application, and only for concentrations of 200 μg g−1. Substrate-induced respiration was temporarily depressed by 200 μg g−1 picloram and 2,4-D, and briefly enhanced by 200 μg g−1 glyphosate. It is concluded that because changes in microbial variables only occurred at herbicide concentrations of much
higher than that which occurs following field application, the side-effects of these chemicals is probably of little ecological
significance. 相似文献
65.
Influence of single amino acids on the development of hamster one-cell embryos in vitro 总被引:1,自引:0,他引:1
One-cell hamster embryos placed in culture have always shown a complete block to development at the two-cell stage. In a preliminary study using a chemically defined culture medium containing 20 amino acids (HECM-1), many one-cell embryos were able to escape the "two-cell block" and develop to the four-cell stage. Use of a simpler formulation containing only the amino acids hypotaurine and glutamine revealed marked inhibitory and stimulatory effects of adding the other amino acids. In the first experiment, 19 amino acids were separately examined for effects on one-cell embryo development. Six amino acids (phenylalanine, valine, isoleucine, tyrosine, tryptophan, and arginine) inhibited embryo development (reduced mean cell number; MCN), and three others (glycine, cystine, and lysine) stimulated development (increased MCN), compared with basic medium containing only glutamine and hypotaurine (low control). When the responses with the six inhibitory amino acids were totalled, only 3 of 185 (2%) one-cell embryos reached the six-or seven-cell stage compared to a total of 15 of 76 (20%) embryos that developed to these stages using the three stimulatory amino acids. When tested together in a second experiment, the six inhibitory amino acids significantly reduced the MCN, from 4.28 +/- 0.44 (low control) to 3.71 +/- 0.55. In this group, 17 of 117 (15%) of one-cell embryos reached more than four-cell and only 4 of 117 (3%) reached six- or 7-cell stages, compared with 39 of 117 (33%) and 12 of 117 (10%), respectively, for the basal medium group.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
66.
Michael J. McFarland William J. Jewell 《Journal of industrial microbiology & biotechnology》1990,5(4):247-257
Summary The continuously operated suspended growth anaerobic contact system was utilized to estimate the effect of sulfate reduction on the thermophilic (55°C) methane fermentation process. Results indicated that reduction in methanogenesis in the presence of sulfate was due to two separate, but related, processes;i.e. competitive and sulfide inhibition. Although prevention of competitive inhibition would be difficult under normal fermenter operation, sulfide inhibition could be minimized by environmental selection of sulfide tolerant microbial populations through biomass recycle and pH control. Stable fermenter operation was achieved at soluble sulfide concentrations as high as 330 mg/l soluble sulfide. Using batch fermenters, a maximum thermophilic sulfate reduction rate of 3.7 mg SO4
2––S/g volatile solids (VS)-day was estimated. The importance of reporting sulfate reduction rates on a biomass basis is demonstrated by a simple population adjustment kinetic model.This research study was conducted at the Department of Agricultural Engineering, Cornell University, Riley Robb Hall, Ithaca, NY 14853, U.S.A. 相似文献
67.
68.
In yeast the GCN2 kinase mediates translational control ofGCN4 by phosphorylating the subunit of eIF-2 in response to extracellular amino acid limitation. Although phosphorylation of eIF-2 has been shown to inhibit global protein synthesis, amino acid starvation results in a specific activation effect onGCN4 mRNA translation. Under the same conditions, translation of other mRNAs appears only slightly affected. The mechanism responsible for the observed selectivity of the GCN2 kinase is not clear. Here, we present genetic evidence that suggests that locally restricted action of the GCN2 kinase facilitatesGCN4-specific translational regulation. 相似文献
69.
Cholinesterase activities in rat forebrain, erythrocytes, and plasma were assessed after a single oral administration of metrifonate
or dichlorvos. In 3-month-old rats, the dichlorvos (10 mg/kg p.o.)-induced inhibition of cholinesterase reached its peak in
brain after 15–45 min and after 10–30 min in erythrocytes and plasma. Cholinesterase activity recovered rapidly after the
peak of inhibition, but did not reach control values in brain and erythrocytes within 24 h after drug administration. The
recovery of plasma cholinesterase activity, in contrast, was already complete 12 h after dichlorvos treatment. Metrifonate
(100 mg/kg p.o.) had qualitatively similar inhibition kinetics as dichlorvos, albeit with a slightly delayed onset. Peak values
were attained 45–60 min (brain) and 20–45 min (blood), after drug administration. Apparently complete recovery of cholinesterase
activity was noted in both tissues 24 h after treatment. The dose-dependence of drug-induced inhibition of cholinesterase
in rat blood and brain was determined at the time of maximal inhibition, i.e., 30 min after dichlorvos treatment and 45 min
after metrifonate treatment. The oral ED50 values obtained for dichlorvos were 8 mg/kg for brain and 6 mg/kg for both erythrocyte and plasma cholinesterase. The corresponding
oral ED50 values for metrifonate were 10 to 15 times higher, i.e., 90 mg/kg in brain and 80 mg/kg in erythrocytes and plasma. In rats
deprived of food for 18 h before drug treatment, the corresponding ED50 values for metrifonate were 60 and 45 mg/kg, respectively, indicating an about two-fold higher sensitivity of fasted rats
to metrifonate-induced cholinesterase inhibition compared to non-fasted rats. Compared to 3-month-old rats, 19-month-old rats
showed a higher sensitivity towards metrifonate and dichlorvos. At the time of maximal inhibition, there was a strong correlation
between the degree of cholinesterase inhibition in brain and blood. These results demonstrate that single oral administration
of metrifonate and dichlorvos induces an inhibition of blood and brain cholinesterase in the conscious rat in a dose-dependent
and apparently fully reversible manner. While the efficiency of a given dose of inhibitor may vary with the satiety status
or age of the animal, the extent of brain ChE inhibition can be estimated from the level of blood ChE activity. 相似文献
70.
Treatment of Gaucher disease with an enzyme inhibitor 总被引:5,自引:0,他引:5
Norman S. Radin 《Glycoconjugate journal》1996,13(2):153-157
The hypothesis is offered predicting that Caucher patients could be treated with a drug that slows the synthesis of glucosylceramide, the lipid that accumulates in this disorder. The present therapeutic approach involves augmenting the defective enzyme, glucosylceramide -glucosidase, with exogenous -glucosidase isolated from human tissue. This spectacularly expensive mode of treatment should be replaceable with a suitable enzyme inhibitor that simply slows formation of the lipid and matches the rate of synthesis with the rate of the defective, slowly working -glucosidase. Several drugs that possess this ability are available, the best known of which is 1-phenyl-2-decanoylamino-3-morpholino-1-propanol (PDMP), a designer inhibitor that resembles the synthase's substrate and product. PDMP has been found to be effective in mice, rats, fish, and a wide variety of cultured cells. Its use, at suitable dosages, seems to be harmless, although long-term tests have not been made. The lack of suitable animal models of Gaucher disease has made it difficult to test the hypothesis adequately, but PDMP does rapidly lower the levels of glucosylceramide in normal animal tissues and the animals evidently do well with the lowered levels of glucosylceramide and its more complex glycolipid metabolites.Abbreviations PDMP
1-phenyl-2-decanoylamino-3-morpholino-1-propanol
- GlcCer
glucosylceramide
- i.p.
intraperitoneal 相似文献