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41.
In a previous work (Kömen et al. 1991) it has been concluded that membrane fragments isolated from autotrophically grown Alcaligenes eutrophus H16 contain several iron-sulphur centres along with haems of a-, b-, c-, and d-type. These redox components have been proposed to be part of a branched respiratory chain leading to multiple membrane bound oxidases. Here, some of the respiratory activities catalyzed by membrane fragments from wild type cells of A. eutrophus (H16) and, for comparison, Paracoccus denitrificans, have been investigated through the use of electron transport inhibitors. Cyanide (CN-) titration curves indicated that in A. eutrophus H16 oxidation of succinate and H2 preferentially proceeds via the cytochrome c oxidase(s) branch (I 50=2 · 10-5 M) whereas the NADH dependent respiration started being inhibited at higher CN- concentrations (I 50=5 · 10-4 M). In membranes isolated from both, cells harvested at late growth-phase (OD 12) and from a mutant deficient in cytochrome c oxidase activity (A. eutrophus RK1), respiration was insensitive to low CN- concentrations (< 10-4 M), and it was sustained by the high catalytic activities of two quinol oxidases. These alternative oxidases of b- (formally o-) and d-type showed different sensitivities to KCN (I 50=10-3 M and 10-2 M, respectively). Interestingly, the cytochrome c oxidase(s) dependent respiration of H16 membranes was insensitive to antimycin A but largely inhibited by myxothiazol (10-6 M). This, and previous work (Kömen et al. 1991), suggest that although the respiratory chain of A. eutrophus is endowed with a putative bc 1 complex, its biochemical nature and role in respiration of this organism are apparently different from those of P. denitrificans. The peculiarity of the respiratory chain of A. eutrophus is confirmed by the rotenone insensitivity of the NADH oxidation in both protoplasts and membrane fragments from wild type and soluble hydrogenase deficient cells (HF14 and HF160). A tentative model of the respiratory chain of autotrophically grown A. eutrophus is presented. 相似文献
42.
Summary We have isolated and characterized a new mutant of Saccharomyces cerevisiae, carrying a single mutant allele that we designate ngm2-1, which is defective with respect to induced mutagenesis. This mutant was isolated by screening mutagenized clones for reduced frequencies of reversion of the his1-7 allele, induced by N-methyl-N-nitro-N-nitrosoguanidine. As judged by the reversion of his1-7 and ilv1-92, ngm2-1 mutant strains are also deficient with respect to mutability induced by methyl methane sulfonate, ethyl methane sulfonate and, at least partially, by UV. UV-induced reversion of the ochre mutation arg4-17 and the frameshift mutation his4-38 was not much affected by ngm2-1, however. Like rev3 and rev7 mutations, ngm2-1 also has little influence on the reversion of the proline missense allele, cyc1-115. Ngm2-1 mutants are only at best very slightly more sensitive to the toxicity of the four mutagens used, and homozygous diploids sporulate normally. 相似文献
43.
A Chinese hamster ovary triple auxotroph (CHO AUXB1) requires glycine, adenosine, and thymidine (GAT) for growth and survival due to a defect in the structural gene for folylpolyglutamate synthetase (FPGS). This auxotroph and others like it contain less than 3% of the parental amounts of FPGS activity. In order to develop a reverse mutation assay with CHO AUXB1, we determined the optimal conditions for measuring reversion and characterized some of the revertants. We also obtained quantitative mutagenicity data for several direct-acting mutagens for comparison to the parental CHO-S/HGPRT locus. Induced revertants appear in the culture immediately following 20-22 h exposures in +GAT complete medium, indicative of dominant genetic changes. They are maximally expressed after 2 population doublings and can be conveniently selected after 44-48 h of expression growth by plating 1 X 10(6) cells/100-mm dish into -GAT-deficient medium and incubating 12-13 days. Plating reconstruction experiments show that the cloning efficiencies of revertants in -GAT medium are not influenced by the presence of up to 1 X 10(6) CHO AUXB1 cells. Dose-dependent increases above the spontaneous revertant frequency (average = 5 X 10(7)) are induced with cis-Pt(NH3)2Cl2 (14-fold) (but not trans-Pt(NH3)2Cl2), PtCl4(10-fold), Pt(SO4)2 (14-fold), K2CrO4 (8-fold), EMS (10-fold), 4-NQO (53-fold), ICR-191 (60-fold), and ICR-170 (30-fold). All of the revertants that have been isolated are stable to repeated subculturing in -GAT medium; 40 out of 42 that have been analyzed are characterized by an increased 72-h growth incorporation of labeled folate and their extracts contain 5-94% as much FPGS as the original, parental CHO-S line. Spontaneous and induced reversion to the GAT+ phenotype primarily reflects mutations involving the FPGS gene locus. But the re-acquisition by most of the revertants of much less than normal amounts of FPGS activity suggests that they arise from compensatory second-site mutations within this gene. Comparison of the mutagenicity patterns of the foregoing compounds as a function of the applied concentration and the relative percent survival reveals some interesting similarities, as well as differences, between the CHO AUXB1/FPGS and CHO-S/HGPRT loci. In particular, the FPGS locus is rather insensitive to EMS (or other simple alkylating agents). However, it seems to be quite susceptible to reversion by other chemicals that are known to react selectively with guanine bases in DNA. CHO AUXBI is a useful supplemental mammalian assay system for assessing quantitatively the generally weak mutagenic activities of metal compounds. 相似文献
44.
Molecular Genetic Analysis of Myelin-Deficient Mice: Shiverer Mutant Mice Show Deletion in Gene(s) Coding for Myelin Basic Protein 总被引:17,自引:6,他引:11
45.
Summary Insight on the function of gangliosides. can emerge from knowledge of their cellular distribution. In this paper we review the structure of ganglioside GD3 and recent information on its cellular distribution. GD3 appears to be enriched in a variety of neural cell types including: reactive glia, gliomas, undifferentiated neurons, Muller glia, and oligodendroglia. Because each of these cell types share an enhanced permeability to ions and metabolites or possess properties associated with enhanced permeability, we suggest that GD3 is associated with enhanced membrane permeability. A possible function for GD3 in membrane permeability has implications for other cellular events such as metabolism, growth and interactions. 相似文献
46.
Thomas Hansen-Hagge Volker Lehmann Ulrich Seydel Buko Lindner Ulrich Zähringer 《Archives of microbiology》1985,141(4):353-358
The extraction, purification and structural characterization of two lipid A precursors (Ia and Ib) differing only in one hexadecanoic acid are described. Both precursors were synthesized at elevated temperatures by a new mutant of Salmonella typhimurium (mutant Ts5) which is conditionally defective in synthesis of the 3-deoxy-d-manno-octulosonic acid region of lipopolysaccharides.Both precursors were purified by repeated phenol/chloroform/petroleum ether (PCP) extractions followed by thin layer chromatography. Teh precursor preparation was free of lipopolysaccharides and phospholipids and contained less than 0.1% protein. Structural analysis which included chemical degradation procedures as well as positive ion laser desorption (LDMS) mass spectroscopy of dephosphorylated lipid A precursors showed together that precursor Ia represents a diphosphorylated glucosamine disaccharide containing two ester, two amide-linked residues of 3-hydroxytetradecanoic acid and lacks the ester-linked dodecanoic, tetradecanoic and hexadecanoic acid as well as 3-deoxy-d-manno-octulosonic acid. Precursor Ib has the same basic structure as precursor Ia, but contains in addition one mol of hexadecanoic acid per mol disaccharide which is linked to the 3-hydroxy group of the amide-bound 3-hydroxy-tetradecanoic acid of the reducing, terminal glucosamine residue.The structure of precursor Ib supports the conclusion that hexadecanoic acid incorporation occurs at an early stage in lipid A biosynthesis prior to the attachment of 3-deoxy-d-manno-octulosonic acid and/or other polar substituents.Abbreviations LDMS
laser desorption mass spectrometry
- KDO
3-Deoxy-d-manno-octulosonic acid
- Ts5
Salmonella typhimurium mutant Ts5
- PCP
phenol/chloroform/petroleum ether
- H2F2
hydrogen fluoride
This work is dedicated to Prof. Dr. Drews, Freiburg, on the occasion of his 60th birthday 相似文献
47.
Summary Stamenless-2 (sl2/sl2) is a temperature-sensitive mutant of tomato (Lycopersicon esculentum) which exhibits altered stamen development under different temperatures (Sawhney 1983). By using scanning electron microscopy, this study was conducted to investigate the differentiation of surface features of mutant and normal stamens grown under different temperatures, with the view to further determine the role of temperature in gene expression in stamen development. Mutant stamens grown under intermediate temperatures (23 °C day/18 °C night) differed from the normal in hair production, the shape of epidermal cells and in the pattern of cuticular thickenings. Under low temperatures (18 °C day/15 °C night), all surface features of mutant stamens closely resembled the normal, whereas under high temperatures (28 °C day/23 °C night), the patterns and types of hairs, epidermal cells, stomata, and cuticular thickenings on mutant stamens were similar to that of a gynoecium. The staminal features of normal stamens were not affected by different temperatures. This study shows that the expression of the sl2/sl2 allele is influenced by temperature conditions to the extent that the pattern of cellular differentiation characteristic of either the stamens or the carpels can be induced in mutant stamens. 相似文献
48.
Selenocysteine lyase activity was detected in crude extracts from a cysteine-requiring mutant ofEscherichia coli K-12. The level of activity was the same whether cells had been grown aerobically or anaerobically, with or without selenocysteine.
Selenocysteine lyase catalyzes the conversion of selenocysteine to alanine and elemental Se, a reaction that is followed by
a nonenzymatic reduction of the Se to hydrogen selenide. Both of these end products were identified in this study. With cysteine
as the substrate, alanine and H2S were formed, but only at levels 50% less than the products formed from selenocysteine. Selenocysteine lyase has been identified
in a number of mammals and bacteria; its presence in a cysK mutant ofE. coli K-12 suggests a common route whereby hydrogen selenide, derived from selenocysteine, can then be assimilated into selenoproteins. 相似文献
49.
A chlorophyll b-less mutant of Chlamydomonas reinhardtii (Pg
27) was isolated after UV irradiation of the wild type cells. This photosynthetically competent mutant totally lacks chlorophyll b and the CP2 chlorophyll-protein complex. However, SDS-PAGE, proteolytic digestions and immunodetections demonstrated that the 24–25 Kd apoproteins of the lacking CP2 complex are still present in thylakoids of the Pg27 mutant. It is concluded that this CP2-less mutant is affected in the biosynthesis pathway of chlorophyll b.This CP2-less mutant was crossed with a CP1-less mutant (Fl5) Fluorescence emission spectra and fluorescence inductions in the presence of DCMU were analysed in the resulting (cp
2
–
, cp
1
+
), (cp
2
+
, cp
1
–
), (cp
2
+
, cp
1
+
), cp
2
–
, cp
1
–
)tetratype. Differences in PS 2 optical cross section and in the relative amplitude or localisation of fluorescence emission peaks fit well with a quadripartite model where PS1 and PS2 would each correspond to a reaction centre core complex (CP1 and CP2 respectively) associated to a light harvesting antenna (LHC1 and LHC2 respectively). The occurrence of energy transfers from PS1 peripheral antenna to PS2 in the Fl
5 mutant shows that, in absence of CP1, at least a part of its associated PS1 light harvesting antenna migrates in the PS2 containing appressed thylakoids.Abbreviations Chl
Chlorophyll
- LHC
Light harvesting chl a/b complex
- CP2
Predominant form of LHC or SDS polyacrylamide gels
- WT
Wild type
- DM
Double mutant (cp
1
–
, cp
2
–
)
- SDS-PAGE
sodium dodecyl sulfate polyacrylamide gel electrophoresis
- DOC-PAGE
Deoxycholate polyacrylamide gel electrophoresis 相似文献
50.
P. C. Banerjee 《Archives of microbiology》1986,144(4):405-407
Phosphoglucose isomerase negative mutant of mucoid Pseudomonas aeruginosa accumulated relatively higher concentration of fructose 1,6-bisphosphate (Fru-1,6-P2) when mannitol induced cells were incubated with this sugar alcohol. Also the toluene-treated cells of fructose 1,6-bisphosphate aldolase negative mutant of this organism produced Fru-1,6-P2 from fructose 6-phosphate in presence of ATP, but not from 6-phosphogluconate. The results together suggested the presence of an ATP-dependent fructose 6-phosphate kinase (EC 2.7.1.11) in mucoid P. aeruginosa.Abbreviations ALD
Fru-1,6-P2 aldolse
- DHAP
dihydroxyacetone phosphate
- F6P
fructose 6-phosphate
- G6P
glucose 6-phosphate
- Gly3P
glyceraldehyde 3-phosphate
- KDPG
2-keto 3-deoxy 6-phosphogluconate
- PFK
fructose 6-phosphate kinase
- PGI
phosphoglucose isomerase
- 6PG
6-phosphogluconate 相似文献