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31.
Elaine J. Davis Joel M. Blatt Eva K. Henderson Joseph J. Whittaker Julius H. Jackson 《Molecular & general genetics : MGG》1977,156(3):239-249
Summary Spontaneous mutants (146) of Escherichia coli K-12 were selected that were resistant to inhibition of growth by 1.2 mM L-valine (Valr). The Valr isolates, containing acetohydroxy acid synthase resistant to feedback inhibition by L-valine (AHASr), were classed according to cotransduction of the mutation with leu. Several mutations resulting in an AHASr phenotype were found to be cotransducible with glyA. However, no mutations causing a Valr phenotype were linked to ilv. AHAS activity was more closely examined in representatives of three classes of mutants with Valr linked to leu, labeled ilv-660, ilv-661, and ilv-662. The ilvE503 allele in E. coli K-12, known to cause a two- to three-fold derepression of AHAS, was found to affect regulation of synthesis of both valine-sensitive AHAS (AHASs) and AHASr in the mutants containing ilv-660 and ilv-661, whereas it affected repression of AHASs, only, in the mutant containing ilv-662. Further, both AHASs and AHASr in the ilv-661 mutant were repressed by valine, whereas valine did not repress AHASr synthesis in the strain carrying ilv-660 and only partially repressed AHASr in the strain carrying ilv-662. Unexpectedly, AHASr synthesis in strains carrying ilv-660 or ilv-662 was repressible by leucine. The ilv-660 locus appears to be similar in position to ilvH and encodes a product that confers valine-sensitivity upon AHAS activity in the wild-type E. coli K-12. The ilv-660 and ilv-662 loci may normally encode products that influence both the feedback sensitivity of AHAS and control of AHAS biosynthesis. 相似文献
32.
The technical quality of 600 electrocardiograms (ECG''s) was assessed for missing leads and clipping, and graded from 1 to 5 for each of noise, lead drift and beat-to-beat drift. Three subgroups of 200 ECGs each were studied: group A, those obtained by emergency department staff (non-technicians); group B, records obtained by ECG technicians; and group C, telephone-transmitted records obtained by technicians performing all the laboratory work at a smaller, outlying hospital. Records with missing leads, clipping, grade 4 or 5 noise, grade 5 lead drift or grade 5 beat-to-beat drift were classified as unsatisfactory or rejected. With these stringent criteria the rejection rate was 71.0% for group A records, 58.5% for group B and 44.5% for group C. The proportions of records with peak quality (no missing leads or clipping, and grade 1 noise, lead drift or beat-to-beat drift) were 4.5% for group A, 5.5% for group B and 23.0% for group C. Suggested revisions in the grading of technical quality of ECGs are presented. 相似文献
33.
34.
D M Ainsworth C A Smith B D Johnson S W Eicker K S Henderson J A Dempsey 《Journal of applied physiology》1992,72(4):1362-1367
Using chronically instrumented awake tracheotomized dogs, we examined the contributions of vagal feedback to respiratory muscle activities, both electrical and mechanical, during normoxic hypercapnia (inspired CO2 fraction = 0.03, 0.04, 0.05, and 0.06) and during mild treadmill exercise (3, 4.3, and 6.4 km/h). Cooling exteriorized vagal loops eliminated both phasic and tonic mechanoreceptor input during either of these hyperpneas. At a given chemical or locomotor stimulus, vagal cooling caused a further increase in costal, crural, parasternal, and rib cage expiratory (triangularis sterni) muscles. No further change in abdominal expiratory muscle activity occurred secondary to vagal cooling during these hyperpneas. However, removal of mechanoreceptor input during hypercapnia was not associated with consistent changes in end-expiratory lung volume, as measured by the He-N2 rebreathe technique. We conclude that during these hyperpneas 1) vagal input is not essential for augmentation of expiratory muscle activity and 2) decrements in abdominal expiratory muscle activity may be offset by increments in rib cage expiratory muscle activity and contribute to the regulation of end-expiratory lung volume. 相似文献
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37.
1-Methyl-1,4-androstadiene-3,17-dione (SH 489): characterization of an irreversible inhibitor of estrogen biosynthesis 总被引:1,自引:0,他引:1
1-Methyl-1,4-androstadiene-3,17-dione (SH 489) was characterized as a competitive and irreversible inhibitor of human placental aromatase. The compound and the principal predicted metabolites show no endocrinological side effects suggesting that SH 489 should be suitable as a prototype drug for treatment of estrogen-dependent disease states. 相似文献
38.
Previous workers have shown that oligosaccharides and glycopeptides can be separated by electrophoresis in buffers containing borate ions. However, normal fluorography of tritium-labeled structures cannot be performed because the glycans are soluble and can diffuse during equilibration with scintillants. This problem has been circumvented by equilibration of the gel with 2,5-diphenyloxazole (PPO) prior to electrophoresis. The presence of PPO in the gel during electrophoresis does not alter mobility of the glycopeptides and oligosaccharides. After electrophoresis, the gel is simply dried and fluorography performed. This allows sensitive and precise comparisons of labeled samples in parallel lanes of a slab gel and, since mobilities are highly reproducible, between different gels. The procedure is preparative in that after fluorography the gel bands can be quantitatively eluted for further study, without any apparent modification by the procedure. In this report, the procedure is illustrated by fractionation of both neutral and anionic glycopeptides produced by the cellular slime mold Dictyostelium discoideum. 相似文献
39.
The synthesis and characterisation of a novel iodinated bile salt derivative, 125I-labelled 3 beta-azidocholylhistamine, is described. The derivative is handled by rat liver in a similar manner to taurocholate and binding to bovine serum albumin, a well-characterised bile acid-binding protein, is demonstrated. The suitability of the derivative for photoaffinity labelling is assessed. 相似文献
40.
G Henderson A Duncan M Kromberg J Roberts F Sim G Vafidis 《BMJ (Clinical research ed.)》1990,300(6731):1076