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101.
102.
Modulation of the population-dependent growth of the human melanoma line MM96 by serum and a series of 2-oxocarboxylates was analysed by a method offering several useful features. Initial cell attachment was measured by the use of cells prelabelled with [14C] thymidine (C) while the size of the replicating cell population on any particular day was monitored by [3H] thymidine (H) incorporation for that particular 24 hr. the 3H incorporation was normalized for the initial cell attachment as the 3H/14C ratio (H/C), which was found to be little affected by artifacts of precursor equilibration. the method allows large numbers of replicate samples so that quantitation of dose-response relationships is simple and statistically robust, and simultaneous monitoring of cell attachment and growth within the same sample is routine. Not only cell growth, but also attachment to the culture vessel surface was found to be increased by higher seeded population densities, by increasing serum concentration and by pyruvate supplementation. Further investigation of the pyruvate effect showed that all nine of the soluble 2-oxocarboxylates tested were effective for both parameters, with little difference between them which was attributable to molecular structure. Quantitative studies of the potentiation of growth and attachment by increasing cell density or a range of concentrations of 2-oxocarboxylates led to the finding that increments in the growth parameter (H/C) were directly proportional to increments in attachment (C). Such a relationship would be unexpected in ordinary logarithmically-growing cultures. the observation is consistent with the hypothesis that increases in initial cell attachment, whether induced by 2 oxocarboxylates or higher inoculation densities, lead to conditioning of the medium by cell factors which stimulate growth and are produced in amounts proportional to the attached cell numbers. Pyruvate, when present with higher serum concentrations, stimulated growth above the levels accounted for by concomitant increases in cell attachment. Serum also appears to have other potentiating factors in addition to those attributable to its content of 2-oxocarboxylates. Differences in the response to 2-oxocarboxylates of human melanoma cells and human diploid fibroblasts were noted, and suggest that the present observations may be due to unique properties of the melanoma cell. 相似文献
103.
Distorted segregation and linkage of alcohol dehydrogenase genes in Camellia japonica L. (Theacease)
Alcohol dehydrogenase isozymes in Camellia japonica are encoded by two genes, Adh-1 and Adh-2. Both loci are expressed in seeds, and their products randomly associate into intragenic and intergenic dimers. Electrophoresis of leaf extracts reveals only the products of Adh-2. Formal genetic analysis indicated that the two Adh loci are tightly linked (combined estimate of r=0.004). Most segregations fit expected Mendelian ratios, but in some families distorted segregation was observed at Adh-1, Adh-2, or both loci. The deficient progeny class varied across families, and in two apparent backcrosses three rather than two phenotypic classes were recovered. The mechanism underlying these distortions is not known, but evidence is presented that suggests that the phenomenon is genic or segmental in nature. Plausible hypotheses include linkage of the Adh structural genes with a gametophytic self-incompatibility locus, translocation heterozygosity involving the segment bearing Adh-1 and Adh-2, or a combination of these two mechanisms. 相似文献
104.
105.
Meria E. Penttilä K. M. Helena Nevalainen Alain Raynal Jonathan K. C. Knowles 《Molecular & general genetics : MGG》1984,194(3):494-499
Summary The possibility of cloning filamentous fungal genes by expression in the yeast Saccharomyces cerevisiae has been studied. A genome bank of Aspergillus niger was made in E. coli using a yeast cosmid shuttle vector and over 10,000 different cosmid clones were individually isolated. Yeast transformants carrying Aspergillus DNA were screened for the expression of the genes for fungal secreted glycoproteins, -galactosidase, -glucosidase, and amyloglucosidase, and for the expression of fungal genes complementing yeast ura3 and leu2 mutations.Of the five Aspergillus genes studied, only one, -glucosidase, was found to be expressed in yeast, and this at a low level. This suggests that there are essential differences between the genes of yeast and filamentous fungi. 相似文献
106.
107.
Yvonne H. Edwards Sue Povey Kay M. Levan Catherine E. Driscoll Jose Luis Millan Erwin Goldberg 《Genesis (New York, N.Y. : 2000)》1987,8(4):219-232
From the data presented in this report, the human LDHC gene locus is assigned to chromosome 11. Three genes determine lactate dehydrogenase (LDH) in man. LDHA and LDHB are expressed in most somatic tissues, while expression of LDHC is confined to the germinal epithelium of the testes. A human LDHC cDNA clone was used as a probe to analyze genomic DNA from rodent/human somatic cell hybrids. The pattern of bands with LDHC hybridization is easily distinguished from the pattern detected by LDHA hybridization, and the LDHC probe is specific for testis mRNA. The structural gene LDHA has been previously assigned to human chromosome 11, while LDHB maps to chromosome 12. Studies of pigeon LDH have shown tight linkage between LDHB and LDHC leading to the expectation that these genes would be syntenic in man. However, the data presented in this paper show conclusively that LDHC is syntenic with LDHA on human chromosome 11. The terminology for LDH genes LDHA, LDHB, and LDHC is equivalent to Ldhl, Ldh2, and Ldh3, respectively. 相似文献
108.
Efficient preparation of spheroplasts fromCandida utilis, Saccharomyces cerevisiae, andSchizosaccharomyces pombe, using a purified mixture of enzymes fromTrichoderma harzianum, is described. Limitations of other methods, and differences between yeasts are demonstrated. 相似文献
109.
Sulfate inhibition of molybdate assimilation by planktonic algae and bacteria: some implications for the aquatic nitrogen cycle 总被引:5,自引:0,他引:5
Molybdenum is required for both dinitrogen fixation and nitrate assimilation. In oxic waters the primary form of molybdenum is the molybdate anion. Using radioactive [99Mol Na2MoO4, we have shown that the transport of molybdate by a natural assemblage of freshwater phytoplankton is light-dependent and follows typical saturation kinetics. The molybdate anion is strikingly similar to sulfate and we present data to show that sulfate is a competitive inhibitor of molybdate assimilation by planktonic algae and bacteria. The ability of freshwater phytoplankton to transport molybdate is inhibited at sulfate concentrations as low as 5% of those in seawater and at sulfate: molybdate ratios as low as 50 to 100 times lower than those found in seawater, Similarly, the growth of both a freshwater bacterium and a saltwater diatom was inhibited at sulfate: molybdate ratios lower than those in seawater.The ratio of sulfate to molybdate is 10 to 100 times greater in seawater than in fresh water. This unfavorable sulfate: molybdate ratio may make molybdate less biologically available in the sea. The sulfate: molybdate ratio may explain, in part, the low rates of nitrogen fixation in N-limited salt waters. 相似文献
110.
Isolation, characterization and metal-ion-binding properties of the alpha-subunit from S-100a protein. 总被引:2,自引:1,他引:1 下载免费PDF全文
The present experiments were undertaken to investigate the role of the phosphoinositides phosphatidylinositol 4-phosphate (PtdIns-4-P) and phosphatidylinositol 4,5-biphosphate (PtdIns-4,5-P2) in the alpha 1-adrenergic stimulation of respiration in isolated hamster brown adipocytes. Exposure of isolated brown adipocytes to the alpha-adrenergic-receptor agonist phenylephrine provoked a breakdown of 30-50% of the PtdIns-4-P and PtdIns-4,5-P2 after prelabelling of the cells with [32P]Pi. Coincident with the breakdown of phosphoinositides was an accumulation of labelled phosphatidic acid, which continued for the duration of the cell incubation. The time course of phosphoinositide breakdown was defined more precisely by pulse-chase experiments. Under these conditions, phenylephrine caused radioactivity in phosphatidylinositol, PtdIns-4-P and PtdIns-4,5-P2 to fall by more than 50% within 30 s and to remain at the depressed value for the duration of the incubation (10 min). This phospholipid response to alpha-adrenergic stimulation was blocked by exposure of the cells to phorbol 12-myristate 13-acetate (PMA); likewise phenylephrine stimulation of respiration was prevented by PMA. beta-Adrenergic stimulation of respiration and inhibition of respiration by 2-chloroadenosine and insulin were, however, unaffected by treatment with PMA. On the assumption that PMA is acting in these cells as an activator of protein kinase C, these results suggest the selective interruption of alpha-adrenergic actions in brown adipocytes by activated protein kinase C. These findings suggest that breakdown of phosphoinositides is an early event in alpha-adrenergic stimulation of brown adipocytes which may be important for the subsequent stimulation of respiration. The results from the pulse-chase studies also suggest, however, that phenylephrine-stimulated breakdown of inositol phospholipids is a short-lived event which does not appear to persist for the entire period of exposure to the alpha 1-adrenergic ligand. 相似文献