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31.
Gellerich Frank Norbert Kapischke Matthias Kunz Wolfram Neumann Wolfram Kuznetsov Andrey Brdiczka Dieter Nicolay Klaas 《Molecular and cellular biochemistry》1994,133(1):85-104
Summary Cytosolic proteins as components of the physiological mitochondrial environment were substituted by dextrans added to media normally used for incubation of isolated mitochondria. Under these conditions the volume of the intermembrane space decreases and the contact sites between the both mitochondrial membranes increase drastically. These morphological changes are accompanied by a reduced permeability of the mitochondrial outer compartment for adenine nucleotides as it was shown by extensive kinetic studies of mitochondrial enzymes (oxidative phosphorylation, mi-creatine kinase, mi-adenylate kinase). The decreased permeability of the mitochondrial outer membrane causes increased rate dependent concentration gradients in the micromolar range for adenine nucleotides between the intermembrane space and the extramitochondrial space. Although all metabolites crossing the outer membrane exhibit the same concentration gradients, considerable compartmentations are detectable for ADP only due to its low extramitochondrial concentration. The consequences of ADP-compartmentation in the mitochondrial intermembrane space for ADP-channelling into the mitochondria are discussed. 相似文献
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The immunosuppressant FK506 inhibits amino acid import in Saccharomyces cerevisiae. 总被引:4,自引:2,他引:2 下载免费PDF全文
J Heitman A Koller J Kunz R Henriquez A Schmidt N R Movva M N Hall 《Molecular and cellular biology》1993,13(8):5010-5019
The immunosuppressants cyclosporin A, FK506, and rapamycin inhibit growth of unicellular eukaryotic microorganisms and also block activation of T lymphocytes from multicellular eukaryotes. In vitro, these compounds bind and inhibit two different types of peptidyl-prolyl cis-trans isomerases. Cyclosporin A binds cyclophilins, whereas FK506 and rapamycin bind FK506-binding proteins (FKBPs). Cyclophilins and FKBPs are ubiquitous, abundant, and targeted to multiple cellular compartments, and they may fold proteins in vivo. Previously, a 12-kDa cytoplasmic FKBP was shown to be only one of at least two FK506-sensitive targets in the yeast Saccharomyces cerevisiae. We find that a second FK506-sensitive target is required for amino acid import. Amino acid-auxotrophic yeast strains (trp1 his4 leu2) are FK506 sensitive, whereas prototrophic strains (TRP1 his4 leu2, trp1 HIS4 leu2, and trp1 his4 LEU2) are FK506 resistant. Amino acids added exogenously to the growth medium mitigate FK506 toxicity. FK506 induces GCN4 expression, which is normally induced by amino acid starvation. FK506 inhibits transport of tryptophan, histidine, and leucine into yeast cells. Lastly, several genes encoding proteins involved in amino acid import or biosynthesis confer FK506 resistance. These findings demonstrate that FK506 inhibits amino acid import in yeast cells, most likely by inhibiting amino acid transporters. Amino acid transporters are integral membrane proteins which import extracellular amino acids and constitute a protein family sharing 30 to 35% identity, including eight invariant prolines. Thus, the second FK506-sensitive target in yeast cells may be a proline isomerase that plays a role in folding amino acid transporters during transit through the secretory pathway. 相似文献
35.
The aims of this study were to investigate the diet and relative abundance of fruit bats in a lowland Malaysian rain forest and to test the hypothesis that the local assemblage structure of fruit bats varies significantly over time in relation to the availability of food. In total, 352 fruit bats of eight species were captured during 72,306 m2 mist‐net hours of sampling between February 1996 and September 1999. Three species of fruit bats (Balionycteris maculita, Chironax melanocephalus, and Cynopterus brachyotis) that fed on a wide range of “steady state” and “big bang” food resources were captured continuously throughout the study period, with no significant variation in capture rates over time. In contrast, five species that fed exclusively or almost exclusively on “big bang” food resources were sampled intermittently, with significant temporal variation in the capture rates of two species (Cynopterus horsfieldi and Megaerops ecaudatus). Significant variation in the capture rates of the remaining three species (Dyacopterus spadiceus, Eonycteris spelaea, and Rousettus amplexicaudatus) could not be detected due to small sample sizes. Since ephemeral “big bang” food resources were only sporadically available within the study area and were associated with large canopy trees and strangler figs, these results suggest that food abundance, or the availability of specific food items, may be important factors limiting local fruit bat species diversity in old‐growth Paleotropical rain forest. Thus, only three fruit bat species were locally resident within the forest throughout the study period. Therefore, further studies on the ranging behavior and habitat requirements of Malaysian fruit bats are required to assess the adequacy of existing reserves and protected areas. 相似文献
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Altered flower/fruit clusters of the kitul palm used as roosts by the short-nosed fruit bat, Cynopterus sphinx (Chiroptera: Pteropodidae) 总被引:1,自引:0,他引:1
The short-nosed fruit bat (Cynopterus sphinx) creates bell-shaped cavities in flower/fruit clusters of the kitul palm (Caryota urens) by chewing and severing flower and fruit strings. These cavities (stem tents) in which the bats roost are usually about one metre deep and 30 cm in diameter. We observed groups of bats roosting in fully-formed stem tents during the daytime, and the construction and subsequent occupancy of newly formed tent cavities. Stem tents are similar in principle to leaf tents except, instead of being formed when bats chew veins and the surrounding tissues of leaves, stem tents are formed in C. urens when bats completely cut several of the central flower/fruit strings. Flower/fruit strings are mostly severed when they are in an immature stage, at times when they are thin and widely spaced. Once these strings thicken and become heavily-laden with mature fruits, bats cannot penetrate the cluster to sever them. Our observations suggest that a single male enters an immature flower or fruit cluster either from below or the sides and severs the central strings along the peduncle. In early phases of stem-tent construction, C. sphinx severs flower/fruit strings at a rate of about one or two per day, and cluster alteration may continue upwards to two months. Only one immature flower/fruit cluster on a C. urens tree is available for alteration by bats at any given time. That this bat does not roost in the fruit/flower cluster during the day, when a tent is under construction, and the accumulation of chewed flower and fruit strings beneath such a cluster in the morning, suggests that tent construction by C. sphinx is a night-time activity. 相似文献
38.
The purpose of this study was to employ the Salmonella/microsomal assay (Ames test) to investigate the mutagenic potential of a thermostable exotoxin of Bacillus thuringiensis subsp. morrisoni. Bacteria are ideal for the detection of infrequently occurring point mutations because the large number of organisms (200 to 400 million bacteria per plate) exposed to the mutagen at any one time increases the possibility of observing a random mutational event. The exotoxin used in this study was produced using the shaker flask fermentation procedure with mineral casein broth. A Petri dish method of bioassay using fresh bovine feces was used to determine the efficacy of the exotoxin against horn flies. The LD50 was found to be 5.35 μl/g of feces. Five bacterial tester strains were identified and characterized for the genetic markers described by Ames et al. (B. N. Ames et al., 1975, Mutat. Res., 31, 347–364). Appropriate doses of the B. thuringiensis supernatant, solvent or positive control were added to agar plates. The supernatant was tested at five dose levels against all five strains of bacteria. Controls of bacteria only were included for spontaneous reversions. All treatments were performed in triplicate. The numbers of revertant colonies from each set of triplicate plates were averaged and the standard deviation calculated and compared to that found with the solvent control. The negative controls, positive controls, and sterility controls all fulfilled requirements for determination of a valid test. No detectable mutagenic activity was found for the thermostable exotoxin of B. thuringiensis morrisoni. 相似文献
39.
Genetic and biochemical consequences of thymidylate stress 总被引:8,自引:0,他引:8
We have examined the genetic and biochemical consequences of thymidylate stress in haploid and diploid strains of the simple eukaryote Saccharomyces cerevisiae (Bakers' yeast). Previously we reported that inhibition of dTMP biosynthesis causes "thymineless death" and is highly recombinagenic, but apparently not mutagenic, at the nuclear level; however, it is mutagenic for mitochondria. Concurrent provision of dTMP abolishes these effects. Conversely, excess dTMP is highly mutagenic for nuclear genes. It is likely that DNA strand breaks are responsible for the recombinagenic effects of thymidylate deprivation; such breaks could be produced by reiterative uracil incorporation and excision in DNA repair patches. In our experiments, thymidylate stress was produced both by starving dTMP auxotrophs for the required nucleotide and also by blocking de novo synthesis of thymidylate by various antimetabolites. We found that the antifolate methotrexate is a potent inducer of mitotic recombination (both gene conversion and mitotic crossing-over). This suggests that the gene amplification associated with methotrexate resistance in mammalian cells could arise, in part, by unequal sister-chromatid exchange induced by thymidylate stress. In addition, several sulfa drugs, which impede de novo folate biosynthesis, also have considerable recombinagenic activity. 相似文献
40.
Nucleotide sequence of xylE from the TOL pDK1 plasmid and structural comparison with isofunctional catechol-2,3-dioxygenase genes from TOL, pWW0 and NAH7. 下载免费PDF全文
Detailed restriction and nucleotide sequence analysis of the Pseudomonas putida TOL plasmid pDK1 xylE gene revealed significant homology with isofunctional xylE (81.5%) and nahH (78.0%) genes from the TOL pWW0 and NAH7 plasmids. The highest degrees of nucleotide and apparent amino acid conservation (82.2 and 86.4%, respectively) among all three genes were found to exist within a region comprising 264 nucleotides encoding the C terminus. A comparison of localized regions revealed significantly greater homology between xylEpWW0 and xylEpDK1 within the C-terminal region, whereas xylEpWW0 and nahH showed greater similarity at the N terminus. The possibility that xylEpWW0 may represent a genetic hybrid of xylEpDK1 and nahH is discussed. 相似文献