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51.
Twenty-four human rhinovirus serotypes were grown and purified by centrifugation in metrizamide density gradients. These preparations had a lower buoyant density (1.24 g/cm3) and higher specific infectivities (1:24 to 1:240) than did rhinoviruses described previously (E. J. Stott and R. J. Killington, Annu. Rev. Microbiol. 26:503-524, 1972). Binding conditions in which the unique cellular receptors for virus attachment were saturated were determined for each serotype. Competition binding assays between pairs of serotypes allowed 20 of the 24 serotypes to be assigned to the same cellular receptor. The remaining four serotypes appeared to attach to a different cellular receptor. Since most serotypes were chosen for study at random, it seems likely that many of the yet unstudied rhinoviruses will share this common cellular receptor. 相似文献
52.
The means by which normal human serum inhibits the activation of PBMC by OKT3 has been investigated. The Fc portion of intact IgG is shown to be the major inhibitor in human serum of this OKT3-induced stimulation. Furthermore, inhibition by IgG subclasses correlated with their ability to bind to the monocyte Fc receptor, i.e., IgG1 and IgG3 produced greater inhibition than IgG2 and IgG4, and this inhibition was competitive. In contrast, hypogammaglobulinemic serum, IgA, IgM, and F(ab')2 of IgG were not inhibitory relative to intact IgG or Fc of IgG. Because of the similarities between T3 and the idiotype-defined T cell receptor for antigen, these investigations suggest that IgG might modulate the interactions between the T cell recognition complex and anti-idiotype antibody, thus regulating the idiotype network. 相似文献
53.
Arrhenotokously reproducing Hymenoptera and Acarina include many important natural enemies. This reproductive system offers
the opportunity of selection on hemizygous (♂ ♂), with the attendant advantages of an unmasked genotype fully exposed to selection,
in creased frequency of genotypes expressing rare genes, and enhanced discrimination of characters, in all-♂ populations produced
by virgin (♀ ♀). Increased selection intensity and reduced genetic drift may offer additional advantages. The method is limited
to characters displayed by (♂ ♂), and may require labor-intensive techniques and species-specific research. The method has
been shown to be practicable withAphytis holoxanthus DeBach (Hymenoptera: Aphelinidae), an important parasite of the Florida red scale,Chrysomphalus aonidum (L.) (Homoptera: Diaspididae).
相似文献
54.
G. Spassov W. R. Abraham K. Kieslich R. Vlahov D. Krikozian St. Parushev M. Chinova G. Snatzke 《Applied microbiology and biotechnology》1986,23(3-4):206-210
Summary Galanthamin is a medical important alkaloid. Its chemical synthesis gives a racemic product in low yields. Starting with a belladinderivative an enzymatic ring closure should lead exclusively to a chiral product possibly with the native structure. Although this reactions type is unknown in preparative biotransformations a large number of microorganisms were tested, unfortunately without success. On the other hand in the screen transformation products were found resulting from specific dealkylations of the subtrate. The type of metabolite formed was dependent on the fungi utilized for the transformation. Additionally two N-oxides were formed by Septomyxa affinis, one in good yield. It is possible that the chirality of this compound can direct the ring closure preferentially or exclusively to the desired stereoisomer of narwedine. 相似文献
55.
Transfer and amplification of a mutant beta-tubulin gene results in colcemid dependence: use of the transformant to demonstrate regulation of beta-tubulin subunit levels by protein degradation. 总被引:3,自引:1,他引:2 下载免费PDF全文
Total genomic DNA from a temperature-sensitive, colcemid-resistant Chinese hamster ovary (CHO) cell mutant expressing an electrophoretic variant beta-tubulin was used to transform wild-type CHO cells to colcemid-resistant cells at 37 degrees C. Southern blot analysis of the transformant demonstrated the three- to fivefold amplification of one of many beta-tubulin sequences compared with that of the wild type or mutant, thereby identifying a functional tubulin gene in CHO cells. This amplification of one tubulin-coding sequence resulted in a threefold increase in two beta-tubulin mRNA species, suggesting that both species may be encoded by a single gene. Pulse-chase experiments showed that in the transformant, total beta-tubulin was synthesized and degraded faster than in the revertant or wild-type cells, so that the steady-state levels of beta-tubulin and alpha-tubulin were unchanged in the transformant compared with those of wild-type, mutant, or revertant cells. Increased ratios of mutant to wild-type beta-tubulin made the transformant dependent on microtubule-depolymerizing drugs for growth at 37 but not 34 degrees C and supersensitive to the microtubule-stabilizing drug taxol at 34 degrees C. 相似文献
56.
57.
Apparent sucrose uptake. ATPase activity and membrane fluidity changes were studied during the development and senescence of carnation flowers ( Dianthus caryophyllus L., cv. Cerise Royallette). Typical changes associated with senescence of a cut flower, such as respiration, ethylene production and fresh weight, were measured. Concomitant with a rise in respiration and ethylene production and a decline in fresh weight, a sharp decrease in apparent sucrose uptake was observed. Sucrose uptake was pH dependent (pH optimum, 5.5) and influenced by membrane integrity. Apparently, the activity of ATPase is related to sucrose uptake, because similar changes occurred during flower development. In addition, the activity of ATPase was well correlated with membrane fluidity.
It is suggested that sucrose uptake is controlled by ATPase activity, which in turn is modulated by membrane lipid fluidity. The decline in membrane fluidity associated with senescence leads to a corresponding reduction in ATPase activity and sucrose uptake. Further evidence supporting this view comes from experiments in which senescence was enhanced by 1-aminocyclopropane-l-carboxylic acid. It shortened the time to decline in fresh weight, rise in respiration and ethylene production. In parallel, reduction in membrane fluidity, ATPase activity and sucrose uptake were observed. 相似文献
It is suggested that sucrose uptake is controlled by ATPase activity, which in turn is modulated by membrane lipid fluidity. The decline in membrane fluidity associated with senescence leads to a corresponding reduction in ATPase activity and sucrose uptake. Further evidence supporting this view comes from experiments in which senescence was enhanced by 1-aminocyclopropane-l-carboxylic acid. It shortened the time to decline in fresh weight, rise in respiration and ethylene production. In parallel, reduction in membrane fluidity, ATPase activity and sucrose uptake were observed. 相似文献
58.
CONCOMITANT SYNTHESIS OF MEMBRANE PROTEIN AND EXPORTABLE PROTEIN OF THE SECRETORY GRANULE IN RAT PAROTID GLAND 总被引:10,自引:9,他引:1 下载免费PDF全文
Abraham Amsterdam Michael Schramm Itzhak Ohad Yoram Salomon Zvi Selinger 《The Journal of cell biology》1971,50(1):187-200
After enzyme secretion the membrane of the secretory granule, which had been fused to the cell membrane, was resorbed into the cell. Experiments were therefore carried out to test whether formation of new secretory granules involves reutilization of the resorbed membrane or synthesis of a new membrane, de novo, from amino acids. Incorporation of amino acids-14C into proteins of various cell fractions was measured in vivo, 30, 120, and. 300 min after labeling. At all times the specific radioactivity of the secretory granule membrane was about equal to that of the granule's exportable content. At 120 and 300 min the specific radioactivity of the granule membrane and of the granule content was much higher than that of any other subcellular fraction. It is therefore concluded that the protein of the membrane is synthesized de novo concomitantly with the exportable protein. The proteins of the granule membrane could be distinguished from those of the granule content by gel electrophoresis. All major bands were labeled proportionately to their staining intensity. The amino acid composition of the secretory granule membrane was markedly different from that of the granule's content and also from that of the mitochondrial membrane. The granule membrane showed a high proline content, 30 moles/100 moles amino acids. The analyses show that the radioactivity of the granule membrane is indeed inherent in its proteins and is not due to contamination by other fractions. The possibility is considered that the exportable protein leaves the endoplasmic reticulum already enveloped by the newly synthesized membrane. 相似文献
59.
60.
Abraham Schalet 《Molecular & general genetics : MGG》1971,110(1):82-85
Summary In contrast to the wild-type eye color seen when Drosophila melanogaster heterozygous for mal
1/mal
F1 are cultured at 25 C, a mutant eye color is observed in heterozygotes cultured at 29–30 C throughout development. Furthermore, heterozygotes have wild-type eyes upon emergence provided development proceeds at 25 C during either of two critical periods: 1) The third quarter of the 3rd larval instar or 2) an imprecisely defined pupal period beginning less than 12 hours before the visual appearance of brown eye pigment and terminating about the time pigment appears in the wings. 相似文献