How does l-glutamate transport relate to selection of mixed nitrogen sources in Rhizobium leguminosarum biovar trifolii MNF1000 and cowpea Rhizobium MNF2030?

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     

4-aminobutyrate is not available to bacteroids of cowpea Rhizobium MNF2030 in snake bean nodules

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     

Interactions of chiral molecules with an (r)-n-(3,5-dinitrobenzoyl) phenylglycine HPLC stationary phase

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.     

Multiple actions of superoxide dismutase: why can it both inhibit and stimulate reduction of oxygen by hydroquinones?

Superoxide dismutase can either inhibit or stimulate autoxidation of different hydroquinones, suggesting multiple roles for O2.-. Inhibitory actions of superoxide dismutase include termination of O2.(-)-propagated reaction chains and metal chelation by the apoprotein. Together, chelation of metals and termination of O2.(-)-propagated chains can effectively prevent reduction of oxygen. Chain termination by superoxide dismutase can thus account for negligible accumulation of H2O2 without invoking a superoxide:semiquinone oxidoreductase activity for this enzyme. One stimulatory action of superoxide dismutase is to decrease thermodynamic limitations to reduction of oxygen. Whether superoxide dismutase inhibits or accelerates an autoxidation depends on the reduction potentials of the quinone and the availability of metal coordination for inner sphere electron transfers.     

Structures of the tetrahydrogenated menaquinones fromActinomadura angiospora,Faenia rectivirgula,andSaccharothrix australiensis

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.     

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

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。     

中国人线粒体DNA的八种限制酶图及其电镜结构

尽管Anderson等人(1981)已测定了人mtDNA的全部序列,但还不能全面地反映整个人类mtDNA核苷酸序列的情况。因此,在具有代表特征的中国人mtDNA序列被测定之前,为了开展对中国人mtDNA的遗传学研究,笔者构建了中国人mtDNA的8种限制酶图。并通过电镜技术对mtDNA进行了研究,发现了一种周长为2μm的小环状DNA,推测它可能在核DNA和mtDNA之间的信息传递或衰老发生中起到某些作用。     

甜椒花药绒毡层的二型性及其组织化学研究

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。     

应用蛋白印迹法检测鼻咽癌病人血清中抗Epstein—Barr病毒IgA/EA抗体

曾毅等建立了一系列检测EB病毒IgA/VCA和IgA/EA抗体的鼻咽癌早期诊断方法,取得了满意的结果。为了进一步提高对鼻咽癌诊断更为特异的IgA/EA抗体的检出率,我们建立了检测EB病毒IgA/EA抗体的蛋白印迹法。方法敏感特异,结果令人满意。 本法中所用的两个质粒系由本实验室与西德Pettenkofer研究所Wolf教授的实验室合作构建。pUCARG1140和pUC9MBcE3.2质粒均为表达质粒,前者携带着来源于EB病毒Bam