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31.
E.p.r.-spectroscopic studies on the molybdenum-iron site of nitrogenase from Clostridium pasteurianum. 下载免费PDF全文
The e.p.r. spectroscopy of the nitrogenase molybdenum-iron protein from Clostridium pasteurianum was re-investigated. The sharpness of the delta Ms = +/- 3 g'z peak from the +/- 3/2 Kramer's doublet enables the observation and quantification of incompletely resolved hyperfine splittings from the stable magnetic nuclei 95Mo and 57Fe in samples enriched in these isotopes. No couplings to 1H or 17O could be discerned by examination of spectra from samples exchanged into 2H2O and H2(17)O respectively. Simulation of the spectrum from 95Mo-enriched samples yields a hyperfine coupling of 2.9 MHz, and indicates that the earlier electron-nuclear-double-resonance-derived estimate of 8.1 +/- 0.2 MHz is substantially in error. 相似文献
32.
Genetic convergence during serial in vitro passage of a polyclonal squamous cell carcinoma 总被引:1,自引:0,他引:1
A cell line was established from an in situ squamous cell carcinoma of the skin (Bowen's disease), and its in vitro karyotypic evolution was cytogenetically analyzed. Initially, considerable genetic heterogeneity was evident. Nine cytogenetically abnormal clones, eight of which were apparently unrelated, were found among the 83 metaphases analyzed from the primary culture and the first passage. With increasing time in culture this complexity was reduced, so that a single clone dominated passages 7-11. The clone that emerged from this genetic convergence had a t(12;17)(p13;q21) as the sole abnormality. Our findings indicate that the cytogenetic multiclonality that has been repeatedly detected in short-term cultures of squamous cell carcinomas is not caused by the in vitro conditions. Instead, the principles of Darwinian selection apply: the altered, but stable, selection pressure facing a newly established and initially multiclonal cell line will lead to a reduction of genetic heterogeneity until the one clone that now has the proliferative advantage outgrows the other subpopulations. 相似文献
33.
When growing on a mixture of ammonia and l-glutamate as nitrogen sources, Rhizobium leguminosarum biovar trifolii MNF1000 utilizes ammonia exclusively, while cowpea Rhizobium MNF2030 utilizes both compounds at similar rates. l-Glutamate transport in both strain MNF1000 and MNF2030 is active, giving rise to a 60-fold concentration gradient across the membrane of cells of strain MNF2030. Both strains produce two kinetically distinguishable glutamate transport systems under all conditions of growth — a high affinity system with an apparent K
m of 0.06–0.17 M but of relatively low V
max, and a low affinity system with a K
m of 1.2–6.7\ M, but of higher overall capacity. l-Glutamate transport activity in cells of MNF2030 was relatively insensitive to the presence of ammonia in the growth medium. By contrast, ammonia in the growth medium resulted in low activities of glutamate transport in cells of MNF1000 which were provided with a carbon source, offering one explanation for the failure of this strain to use glutamate in the presence of ammonia. However, in cells of MNF1000 growing on glutamate as sole source of carbon and nitrogen, the glutamate transport system is synthesized, even in the presence of accumulated or added ammonia. This suggests that the regulation of the glutamate permease also depends on availability of carbon source.Abbreviations CCCP
carbonyl cyanide m-chlorophenyl hydrazone
- HEPES
N-hydroxyethylpiperazine-N-2-ethanesulphonic acid 相似文献
34.
4-aminobutyrate is not available to bacteroids of cowpea Rhizobium MNF2030 in snake bean nodules 总被引:1,自引:0,他引:1
Laboratory cultures of cowpea Rhizobium MNF2030 grew on 4-aminobutyrate (GABA) as sole source of carbon and nitrogen. GABA transport was active since it was inhibited by carbonyl cyanide mchlorophenyl hydrazone and 2,4-dinitrophenol and cells developed a 400-fold concentration gradient across the cell membrane. Arsenite treatment of GABA-grown cells revealed stoichiometric conversion of GABA to pyruvate, indicating that 2-oxoglutarate is not an intermediate in GABA catabolism. GABA catabolism by cells of strain MNF2030 grown on GABA appreared to involve GABA transaminase, succinic semialdehyde dehydrogenase and malic enzyme; the first two enzymes were specifically induced by growth on GABA. The deamination process and removal of NH3 in cells catabolizing GABA involved GABA: 2-oxoglutarate transaminase; glutamate: oxaloacetate aminotransferase; asparate: pyruvate aminotransferase and alanine dehydrogenase.Isolated snakebean bacteroids of strain MNF2030 transported only small amounts of GABA and had uninduced levels of GABA catabolic enzymes, even though the nodules contained significant levels of GABA. The data suggest that GABA is not available to snakebean nodule bacteroids, presumably because of a control imposed by the peribacteroid membrane.Abbreviations
CCCP
Carbonyl cyanide m-chlorophenyl hydrazone
-
HEPES
N-hydroxyethylpiperazine-N-2-ethanesulphonic acid
-
DTT
dithiothreitol
-
SSAD
succinic semialdehyde dehydrogenase
-
GABAT
4-aminobutyrate transaminase
-
GABA
4-aminobutyrate 相似文献
35.
Forty different chiral molecules were studied by liquid chromatography with a Pirkle-type, (R)-N-(3,5-dinitrobenzoyl) phenylglycine (DNBPG), chiral stationary phase column. The dramatic effect of a small molecular change on chiral recognition was demonstrated using DL-amino acid derivatives. The inductive effect on chiral recognition was also studied using trifluoro-, trichloro-, dichloro-, monochloroacetyl, and acetyl derivatives of four different chiral amines. The study of the enantiomer separation of 11 different crown ethers of 2,2′-binaphthyldiyl showed that the rigidity of the chiral center can be an additional parameter in chiral recognition for the DNBPG phase but not for a β-cyclodextrin bonded chiral phase. It is apparent from this study that steric effects, inductive effects, and molecular rigidity play important roles in chiral recognition with DNBPG chiral stationary phases. 相似文献
36.
Dr. Matthew D. Collins Reiner M. Kroppenstedt Jin Támaoka Kazuo Komagata Takeshi Kinoshita 《Current microbiology》1988,17(5):275-279
The structures of the tetrahydrogenated menaquinones fromActinomadura angiospora, Faenia rectivirgula, andSaccharothrix australiensis were determined by mass spectrometry and proton nuclear magnetic resonance spectrometry. The positions of saturation of the tetrahydrogenated menaquinones fromFaenia rectivirgula andSaccharothrix australiensis were units II plus III (counting from the ring system), whereas that ofActinomadura angiospora had units III and VIII hydrogenated. The tetrahydrogenated menaquinones fromFaenia rectivirgula andSaccharothrix australiensis are similar to those characterized from other Gram-positive taxa to date, whereas that fromActinomadura angiospora represents a hitherto unknown isomer. 相似文献
37.
从“湖北光敏感核不育水稻”的未受精子房和花药培养出单倍体植株 总被引:10,自引:0,他引:10
采用10种诱导培养基,培养湖北光敏感核不育水稻农垦58品种的未受精子房和花药。共培养未受精子房2790个,获得胚囊愈伤组织17块,最高诱导频率达3.33%,其中2块分化出绿苗。培养花药16740个,获得花药愈伤组织15块,最高诱导频率为0.92%,其中3块分化出苗,2丛白苗,1株绿苗。胚囊植株和花粉植株经根尖染色体检查为单倍体,2n=x=12。实验证明,液体培养、2,4-D0.2-0.5 mg/1、低温预处理对诱导胚囊愈伤组织及花粉愈伤组织的形成具良好效果。 相似文献
38.
39.
在甜椒(Capsicum annuum L.)中,靠近花粉中部的绒毡层自药隔产生,由较大的细胞组成,而花药外部区域的其余的绒毡层细胞较小,来自于初生壁层,前者的细胞具有大液泡和较大的细胞核,甲基绿-派罗宁和汞-溴酚蓝染色反应较后者弱,在造孢组织时期,二者液泡内都含有较大的球形的酸性磷酸酶颗粒,在以后的发育中,这种颗粒消失,在减数分裂时期,两种绒毡层的DNA,RNA和蛋白质合成活动增强,来自药隔的绒毡层积累了更多的DNA,绒毡层在解体时酸性磷本酶活性很高,两种不同的绒毡层退化过程相似,在全部发育过程中绒毡层内无淀粉粒。 相似文献
40.