Biosynthetic Pathway of Thiamine Pyrophosphate: a Special Reference to the Thiamine Monophosphate-Requiring Mutant and the Thiamine Pyrophosphate-Requiring Mutant of Escherichia coli

alpha-Isopropylmalate synthase, the first specific enzyme in leucine biosynthesis, was purified approximately 100-fold from extracts of Saccharomyces sp. (strain 60615), the most effective step being specific elution with the feedback inhibitor leucine from a hydroxyapatite column. In the early steps of purification, special care was taken to protect the synthase against proteolytic activities. The apparent molecular weight of the enzyme as determined from gel filtration on a calibrated column was 137,000 in the absence and 121,000 in the presence of leucine. Inhibition by leucine was specific and strongly pH-dependent, with the leucine concentration necessary for half-maximal inhibition increasing about 10-fold as the pH increased from 7.5 to 8.5. Within this pH range, catalytic activity remained almost unchanged. The apparent K(m) values for the two substrates were found to be 16 mum for alpha-ketoisovalerate and 9 mum for acetyl-coenzyme A. K(+) was required for full activity, the apparent K(a) value being 2 mm. Leucine inhibition was of the mixed type, resulting in decreased V(max) and increased apparent K(m) values forboth substrates. Whereas no cooperative effects were observed with either substrate, positive cooperativity was seen with leucine in the presence of saturating substrate concentrations. Leucine and, to a lesser extent, alpha-ketoisovalerate stabilized the purified enzyme against heat-inactivation. The presence of acetyl-coenzyme A, on the other hand, accelerated the inactivation. In subsequent experiments, coenzyme A was recognized as the actual inactivating ligand, being effective even at lower temperatures and in concentrations which were estimated to be in the range of the enzyme concentration.     

Chromosomal rearrangements in Plantago insularis Eastw.

Seeds of Plantago insularis Eastw. which were irradiated with gamma rays yielded 37–67% semi-sterile plants. Twenty-four out of sixty-four of these plants were heterozygous for one or more chromosomal rearrangements. Twothirds of these were translocations, and one-third were inversions. Homozygous lines for four translocations were established. The karyotypes of these provide chromosome markers either at pachynema or in mitotic divisions, or both.Breakage positions were usually located within hetrochromatic segments or at the ends of heterochromatic regions (72.6% of all breaks), and half of all breaks occurred at the juncture of the centromere with the proximal heterochromatin. The consequences of proximal breakage were non-random, in that 93% of such breaks resulted in translocations and only 7% in inversions, whereas more than half of breaks in non-centromeric regions became involved in inversions.The individual chromosomes differed in the types of breakage and of aberrations produced, and these differences appeared correlated with length ratios of heterochromatic segments flanking the centromeres.The research for this paper was supported by National Science Foundation Grant Number GB 5713X.     

Biosynthesis of Thiamine Pyrophosphate in Escherichia coli

In Escherichia coli, thiamine pyrophosphate is synthesized from thiamine monophosphate. Free thiamine is not involved as an intermediate in de novo synthesis of thiamine pyrophosphate.     

Inhibition of Thiamine Pyrophosphate Utilization by Thiamine or Its Monophosphate in Escherichia coli

The growth of a thiamine pyrophosphate auxotroph of Escherichi coli was inhibited by either thiamine or thiamine monophosphate, and the growth of a thiamine monophosphate auxotroph was inhibited by thiamine. The thiamine pyrophosphate-dependent oxidation of pyruvate was inhibited by thiamine with whole cells of the thiamine pyrophosphate auxotroph but not with cell extracts prepared from the same organism. In addition, the thiamine pyrophosphate uptake of the thiamine pyrophosphate auxotroph was inhibited by either thiamine or thiamine monophosphate. Although the thiamine pyrophosphate uptake of a revertant, selected for prototrophy from the thiamine monophosphate auxotroph, was inhibited by thiamine to an extent comparable to that observed with the thiamine monophosphate auxotroph, its growth was no longer inhibited by thiamine. A possible mechanism for the inhibition by thiamine and thiamine monophosphate in the utilization of thiamine pyrophosphate is discussed.     

一个新的水稻白化转绿突变体的生理特性和基因定位

秋丰M来源于粳稻秋丰的自然白化转绿突变株。其主要特征为前三叶白化带绿,第四叶及以后叶片均为淡绿色,抽穗时,秋丰M的颖壳和前三叶一样仍出现带绿的白化现象。不同生长时期对野生型和突变型水稻叶片色素含量测定的结果与田间观察结果一致,秋丰M确实存在着一个叶色显著变化的过程。主要农艺性状的比较结果表明,秋丰与秋丰M除穗颈长和千粒重达到极显著差异外,其他农艺性状均无明显差异。遗传分析发现该突变性状受一对隐性核基因控制。以209株培矮64S×秋丰M F_2的隐性突变个体为定位群体,将突变基因定位在水稻第2染色体长臂上,位于 SSR 标记RM475和RM2-22之间,其遗传距离分别为17.3 cM和2.9 cM,并将该基因命名为gra_(t)。     

水稻(Oryza sativa L.)苗期低温白化突变体al12的超微结构与基因定位

水稻苗期低温白化突变是水稻在发育早期对低温胁迫的一种适应性,是一种受发育和温度控制的条件表达,它与其他水稻白化突变有本质的不同.本研究利用便携式叶绿素测量仪测定了白化时期植株的叶绿素含量和用透射电镜观察了叶绿体的结构变化.结果发现叶绿素平均含量仅为1.2(SPAD),而叶绿体也不能正常发育仅有囊泡状结构.通过与9311的正反交实验及子代的分离表现证明该性状受一个隐性核基因的控制.另外利用SSR分子标记技术将该基因定位在第8染色体上,两侧最近的SSR标记RM5068和RM3702分别距基因0.5～1.1 cM和4.9 cM,基因被定位在约6个cM的区间内.我们将该基因暂时命名为al12.     

黑线仓鼠及其白化突变系毛囊中黑色素细胞的组织学分析

目的黑线仓鼠白化突变系是一种新的实验动物模型,本研究旨在组织水平上观察黑线仓鼠与白化突变系皮肤组织中黑色素细胞的分布与定位,以揭示黑线仓鼠白化突变系发生的细胞学机制。方法本实验选择黑线仓鼠和白化突变系各6只,取背部皮肤,制备石蜡切片,分别采用多巴染色、多巴-甲苯胺蓝复染,光镜观察、拍照。结果 Dopa染色显示,在黑线仓鼠与白化突变系皮肤组织中均有成熟黑色素细胞的分布,主要存在于毛囊毛乳头中,且黑线仓鼠黑色素阳性区要明显高于白化突变系。结论黑线仓鼠的酪氨酸酶活性要高于白化突变系。     

Inactivation of ccmO in Synechococcus sp. Strain PCC 7942 Results in a Mutant Requiring High Levels of CO2

Inactivation of ccmO in Synechococcus sp. strain PCC 7942 resulted in a mutant which possesses aberrant carboxysomes and a normal inorganic carbon uptake capability but a reduced ability to photosynthetically utilize the internal inorganic carbon pool. Consequently, it exhibits low apparent photosynthetic affinity for extracellular inorganic carbon and demands high levels of CO₂ for growth.     

浙江淳安千岛湖发现一例白化乌鸫

黄腹角雉(Tragopan caboti)为我国特有雉类,国家一级重点保护野生动物。2010至2021年通过视频监测技术、红外相机监测与人工观察,对浙江省乌岩岭国家级自然保护区内的黄腹角雉巢卵被天敌危害情况进行了调查。基于42个黄腹角雉人工巢监测数据(36巢视频远程监控,2巢红外相机监测,4巢人工观察),野生黄腹角雉巢被天敌破坏的比率为54.8%,其中91.3%被破坏巢中的卵为王锦蛇(Elaphe carinata)所捕食,表明王锦蛇是黄腹角雉巢卵最主要的天敌。捕食黄腹角雉卵的天敌还包括松鸦(Garrulus glandarius)与黄喉貂(Martes flavigula),可能的天敌有灰树鹊(Dendrocitta formosae)、黄腹鼬(Mustela kathiah)及短尾猴(Macaca arctoides)等。本研究基于视频资料揭示了野生黄腹角雉种群的天敌情况,结合文献资料,我们推测黄腹角雉较长的孵卵期与离巢时间可能是造成其巢卵损失率高的主要原因,本研究结果对这一濒危物种的保护与繁育工作具有重要意义。     

Unusual Leucophore‐Like Cells Specifically Appear in the Lineage of Melanophores in the Periodic Albino Mutant of Xenopus laevis

In the periodic albino mutant (a^p/a^p) of Xenopus laevis, peculiar leucophore‐like cells appear in the skins of tadpoles and froglets, whereas no such cells are observed in the wild‐type (+/+). These leucophore‐like cells are unusual in (1) appearing white, but not iridescent, under incident light, (2) emitting green fluorescence under blue light, (3) exhibiting pigment dispersion in the presence of α‐melanocyte stimulating hormone (αMSH), and (4) containing an abundance of bizarre‐shaped, reflecting platelet‐like organelles. In this study, the developmental and ultrastructural characteristics of these leucophore‐like cells were compared with melanophores, iridophores and xanthophores, utilizing fluorescence stereomicroscopy, and light and electron microscopy. Staining with methylene blue, exposure to αMSH, and culture of neural crest cells were also performed to clarify the pigment cell type. The results obtained clearly indicate that: (1) the leucophore‐like cells in the mutant are different from melanophores, iridophores and xanthophores, (2) the leucophore‐like cells are essentially similar to melanophores of the wild‐type with respect to their localization in the skin and manner of response to αMSH, (3) the leucophore‐like cells contain many premelanosomes that are observed in developing melanophores, and (4) mosaic pigment cells containing both melanosomes specific to mutant melanophores and peculiar reflecting platelet‐like organelles are observed in the mutant tadpoles. These findings strongly suggest that the leucophore‐like cells in the periodic albino mutant are derived from the melanophore lineage, which provides some insight into the origin of brightly colored pigment cells in lower vertebrates.     

Inactivation of ccmO in Synechococcus sp. Strain PCC 7942 Results in a Mutant Requiring High Levels of CO(2)

Inactivation of ccmO in Synechococcus sp. strain PCC 7942 resulted in a mutant which possesses aberrant carboxysomes and a normal inorganic carbon uptake capability but a reduced ability to photosynthetically utilize the internal inorganic carbon pool. Consequently, it exhibits low apparent photosynthetic affinity for extracellular inorganic carbon and demands high levels of CO(2) for growth.     

Ultrastructure and Gene Mapping of the Albino Mutant al12 in Rice (Oryza sativa L.)

Seedling albino mutation resistant to low temperature is an adaptability of rice (Oryza sativa L.) to cold. The mutant, a conditional expression controlled by development and temperature, differs from other albino mutants. The chlorophyll content of the mutant was measured using a portable chlorophyll meter, and the ultrastructure of the chloroplast was observed using a transmission electron microscope. Chlorophyll content was 1.2 SPAD, and the chloroplast did not develop, with only small vesicle-like structures. A segregation analysis of the reciprocal crosses between the albino mutation line with the rice line 9311 demonstrated that the albino trait was controlled by a single recessive gene, which was flanked by SSR markers RM5068 and RM3702 on the short arm of chromosome 8 with a distance of 0.5-1.1 cM and 4.9 cM, respectively. This gene was mapped within a 6 cM interval region and was tentatively referred to as al12.     

广西发现版纳鱼螈白化幼体一例

2007年5月,在广西北流市六麻镇捕到一例雄性版纳鱼螈(Ichthyophis bannanicus)白化幼体。该个体完全白化。体重9.1 g,全长195 mm,尾长3.85 mm,体宽10.36 mm,吻长3.09 mm,尾鳍高5.71 mm,吻端至第一环沟9.47 mm,吻端至第二环沟13.41 mm,鼻间距2.42 mm,眼间距5.17 mm。与正常个体对比发现:该白化幼体的尾长、体宽、尾鳍高大于正常范围,吻端至第二环沟小于正常范围,其余数据均在正常范围内。