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51.
The development and vertical distribution of populations of gas-vacuolate bacteria in a eutrophic,monomictic lake 总被引:2,自引:0,他引:2
The role of gas vacuoles in the vertical stratification of planktonic bacteria is analysed. Measurements made with certain gas-vacuolate bacteria in laboratory culture suggest that only colonial forms could sink or float fast enough to form population maxima in lakes by vertical migration from other depths. It is suggested that in the case of individual cells the importance of the buoyancy provided by gas vacuoles is to minimise sinking rates and thereby to increase residence times of the organisms at depths where conditions support their growth.Changes in the vertical distribution of a number of gas-vacuolate bacteria were followed throughout the year in a monomictic, eutrophic lake (Crose Mere, Shropshire). All were restricted to the anaerobic hypolimnion which developed in summer. The various species formed maxima at different depths and times. With some of them (e.g. species of Thiopedia, Pelonema and Brachyarcus) growth was necessary to explain their development. In others (e. g. species of Pelodictyon and two colourless bacteria) vertical migrations might also have contributed to their development. 相似文献
52.
Mathew A. Vadas Jacques F. A. P. Miller Alison M. Whitelaw Jennifer R. Gamble 《Immunogenetics》1977,4(1):137-153
Identity at the major histocompatibility complex (MHC) was essential for successful transfer of delayed type hypersensitivity (DTH) in mice. The regions of the MHC involved differed according to the antigen used for sensitization. In the case of fowl gamma globulin (FGG), identity atI-A was necessary, whereas with dinitrofluorobenzene (DNFB), identity at theK, I, orD region was sufficient. These different genetic constraints probably reflect differences in the mechanisms by which antigens are presented to T lymphocytes. Cells from sensitized (CBA×C57BL)F1 mice transferred DTH to FGG into parental-strain mice, but transfer was more effective in C57BL than in CBA with the same cell dose. This phenomenon is governed by the MHC, since there was better transfer intoH-2
b
than intoH-2
k
mice, regardless of their backgrounds. It may reflect the activity of an Ir gene-dependent process. Cells of one genotype (e.g., CBA), sensitized in chimeric mice derived from two MHC-incompatible strains (CBAC57BL), transferred DTH to both strains. These results do not support the notion that the genetic constraint observed in DTH transfer may be a result of the necessity for sensitized T and stimulator cells to match an identical MHC-coded cell interaction molecule. Rather, they favor the hypothesis that T cells recognize antigen, not as a naked determinant, but in close association with products of genes of the MHC. 相似文献
53.
Defect in macrophage effector function confers Salmonella typhimurium susceptibility on C3H/HeJ mice
The defective allele of the endotoxin response locus (Lpsd) renders mice (e.g., C3H/HeJ strain) both endotoxin hyporesponsive and susceptible to Salmonella typhimurium. In this study, the mechanism of Lpsd-regulated susceptibility to murine typhoid was examined. C3H/ HeJ mice became significantly more resistant to S. typhimurium by reconstitution with bone marrow from syngeneic C3H/HeN mice (Lpsn, salmonella resistant). Thus, the Lpsd resistance defect appeared to reside in a radiosensitive bone marrow-derived cell(s). At least one of the abnormal cell types appeared to be a macrophage because C3H/HeJ mice preinfected with Mycobacterium bovis (BCG) were, in contrast to controls, able to restrict early salmonella replication in their spleens and displayed a signficant increase in mean time to death. In contrast, no deficiency in uptake of salmonellae by C3H/HeJ macrophages was observed. These results indicate that the early deaths of C3H/HeJ mice following S. typhimurium challenge reflect a failure of their macrophages to limit the growth of these gram-negative bacteria. 相似文献
54.
Cerebral Metabolic Effects of Monoamine Oxidase Inhibition in Normal and 1-Methyl-4-Phenyl-1,2,3,6-Tetrahydropyridine Acutely Treated Monkeys 总被引:2,自引:0,他引:2
Ernesta Palombo Linda J. Porrino† Alison M. Crane Krzysztof S. Bankiewicz‡ Irwin J. Kopin‡ Louis Sokoloff 《Journal of neurochemistry》1991,56(5):1639-1646
The neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) induces dopaminergic cell death in the substantia nigra pars compacta (SNpc) and clinical parkinsonism in humans and experimental animals. Pretreatment with monoamine oxidase inhibitors prevents this cell death and associated parkinsonism by blocking the oxidation of MPTP to a toxic intermediate. The 2-deoxyglucose method was used to study the acute effects of MPTP in the monkey brain and the effects of monoamine oxidase inhibition on local cerebral glucose utilization in both normal and MPTP-treated monkeys. MPTP administration alone caused a major increase in glucose utilization in the SNpc and smaller increases in some subnuclei within the ventral tegmental area in which eventual dopaminergic cell loss also occurs. Pretreatment with pargyline abolished these metabolic increases, a finding suggesting both that the oxidized product of MPTP generates the metabolic increases and that the increased glucose consumption may contribute to cell toxicity. On the other hand, in most cortical, thalamic, striatal, brainstem, and cerebellar areas MPTP alone caused reductions in glucose utilization, and pargyline failed to prevent these effects. Pargyline alone depressed metabolism in the locus coeruleus and a few other monoaminergic structures. 相似文献
55.
Dopaminergic neurons from embryonic rat mesencephalon were grown in simple serum-free media. The cells develop over a period of several weeks in vitro, particularly between day 14 and day 23. Removing the culture medium and replacing it with fresh medium during this interval caused severe damage to the cultures; this damage is mediated by excitatory amino acids acting through glutamate receptors. Damage could be completely prevented by antagonists of the N-methyl-D-aspartate subtype of glutamate receptor. As expected, medium that contains glutamate (i.e., Ham's F-12 medium) caused damage; however, medium that contains no glutamate or aspartate (i.e., Dulbecco's modified Eagle medium) also caused severe damage, and most of the damage was dependent on the presence of glutamine in the medium. The presence of the antibiotics penicillin and streptomycin greatly enhanced damage caused by medium change. 相似文献
56.
Soluble starch synthase was purified 10000-fold from developing embryos of pea (Pisum sativum L.). The activity was resolved into two forms which together account for most if not all of the soluble starchsynthase activity in the embryo. The two isoforms differ in their molecular weights but are similar in many other respects. Their kinetic properties are similar, neither isoform is active in the absence of primer, and both are unstable at high temperatures, the activity being abolished by a 20-min incubation at 45° C. Both isoforms are recognised by antibodies raised to the granule-bound starch synthase of pea. Isoform II, which has the same molecular weight (77 kDa) as the granulebound enzyme, is recognised more strongly than Isoform I. 相似文献
57.
58.
Donald Moir Jen-i Mao James W. Schumm Gerald F. Vovis Bernadette L. Alford Alison Taunton-Rigby 《Gene》1982,19(1):127-138
A full-length cDNA copy of the mRNA encoding calf chymosin (also known as rennin), a proteolytic enzyme with commercial importance in the manufacture of cheese, has been cloned in an f1 bacteriophage vector. The nucleotide sequence of the cDNA was determined, and translation of that sequence into amino acids predicts that the zymogen prochymosin is actually synthesized in vivo as preprochymosin with a 16 amino acid signal peptide. In vitro translation of total poly(A)-enriched RNA from the calf fourth stomach (abomasum) and immunoprecipitation with antichymosin antiserum revealed that a form of chymosin (probably preprochymosin judging from the Mr-value) is the major in vitro translation product of RNA from that tissue. Gel-transfer hybridization of restriction endonuclease-cleaved bovine chromosomal DNA with labeled cDNA probes indicated that the two known forms of chymosin, A and B, must be products of two different alleles of a single chymosin gene. 相似文献
59.
60.