柠檬酸合酶的分子生物学研究进展

柠檬酸合酶（citrate synthase,CS）是细胞内多种重要代谢途径的关键酶。CS可催化草酰乙酸和乙酰辅酶A之间的缩合反应生成柠檬酸和辅酶A。通常革兰氏阳性细菌、古菌以及真核细胞的CS为同源二聚体,而革兰氏阴性细菌的CS为同源六聚体。根据其在细胞内的定位不同,CS可分为线粒体CS、乙醛酸循环体CS、过氧化物酶体CS。这些同工酶在能量代谢、植物脂肪的代谢、脂肪酸的氧化及细胞解毒过程中起着重要作用。不同来源的CS空间结构、催化机制和动力学性质十分相似。针对其生化特性、空间结构特点、催化机制以及分子进化等研究进展进行综述。     

Characterisation of Structures in Salivary Secretion Film Formation. An Experimental Study with Atomic Force Microscopy

The purpose of the present study was to characterise the structure dynamics of pure salivary secretions retained on controlled surfaces with different surface energies in the early stage of salivary film formation. Germanium prisms prepared to have either low surface energy or medium surface energy were incubated in fresh secretions of either human parotid saliva (HPS) or human submandibular/sublingual saliva (HSMSLS) for 15, 90, and 180 min. After controlled rinsing with distilled water, the surfaces were air dried and thereafter imaged with atomic force microscopy (AFM). The amount of adsorbed material and the size of the structures detected increased with increased saliva exposure time. The film thicknesses varied from 10 to 150 nm, and both HPS and HSMSLS films contained structures with diameters varying from 40 nm to 2 μm. Some of these were clustered into special formations. The HPS films exhibited a more granular morphology than the HSMSLS films. Furthermore, branched lines were detected on the low surface energy germanium prisms incubated in saliva. The results indicate that exposure time, surface energy, and type of salivary secretion all are factors affecting the adsorption characteristics of salivary films.     

Normale Zweitbruten beim Rothalstaucher(Podiceps griseigena)

Ohne Zusammenfassung     

Transient expression of storage-protein genes during early embryogenesis ofVicia faba: synthesis and metabolization of vicilin and legumin in the embryo,suspensor and endosperm

Seed storage proteins are thought to be accumulated exclusively in the cell-expansion phase of embryogenesis and metabolized during germination and seedling growth. Here we show by a sensitive immunohistological technique that the two Vicia faba L. storage proteins vicilin and legumin are accumulated in substantial amounts in the suspensor and coenocytic endosperm and to a lesser extent in the mid-globular embryo. Both proteins appear and disappear at precise stages specific for each tissue. In the endosperm the accumulation starts around 12 d after pollination (DAP). After a maximum attained at 14–15 DAP, storage proteins are degraded within about 4 d. Accumulation is restricted to that part of the endosperm which covers the embryo and displays the highest levels of endoploidy (maximum 96n). In all other parts of the endosperm, storage proteins do not appear to accumulate, although storage-protein-specific mRNA synthesis takes place. In the suspensor, storage proteins are already observed at 6 DAP and disappear very quickly at approximately 10 DAP. Low amounts of legumin and vicilin are also detectable in the mid-globular embryo, but disappear completely as the embryo enters the heart stage. We conclude that storage proteins of Vicia faba accumulated transiently during early seed development are used as nutritive reserves for the growing embryo.Abbreviation DAP days after pollination Dedicated to Prof. Rigomar Rieger in the occasion of his 65th birthdayThis research was supported by the Ministry of Science and Research, Land Sachsen-Anhalt, Germany. U.W. acknowledges additional support by the Fonds der Chemischen Industrie.     

Controlling seed development and seed size in Vicia faba: a role for seed coat-associated invertases and carbohydrate state

We previously provided evidence that seed coat-associated invertase is involved in controlling the carbohydrate state of developing seeds and, by this way, triggering developmental processes (Weber et al . (1995) Plant Cell , 7, 1835–1846). To verify our postulate, we compared seed development of two genotypes of Vicia faba differing in seed weight. The seed coat of the large-seeded genotype formed a higher number of parenchymatous cell layers and matured later. VfCWINV1 encoding a cell wall-bound invertase is expressed in the unloading zone of the seed coat. mRNA levels peaked later in 'large' coats and mRNA was present in more cell layers over a longer time period. Cell wall-bound invertase activity revealed a similar accumulation pattern, obviously generating the high hexose conditions present in the endospermal cavity bathing the premature cotyledons and thus controlling their carbohydrate state. High hexose conditions were correlated with an extended mitotic activity of the 'large' cotyledons. In 'large' and 'small' cotyledons, sucrose levels rose when hexoses decreased apparently terminating cell divisions and initiating differentiation and storage activities. This developmental switch was delayed in 'large' embryos. To prove the outlined relationship, sucrose was added in vitro to mitotically active cotyledons. This treatment favoured nuclear expansion and starch accumulation over cell division. In contrast, a hexose-based medium maintained cell divisions. We conclude that development of the embryo is coordinately regulated with that of the maternal seed coat which controls, by metabolic signals, the phase of cell division of the embryo and consequently also seed size.     

Tissue specific gene activities and proteins in the Chironomus salivary gland

Summary The secretory proteins of the larval salivary gland of some Chironomus species were analysed according to a method developed by Grossbach (1969). After reduction of the disulphide bonds and alkylation the secretion of Chironomus thummi was separated by disc electrophoresis at acrylamide concentrations of 4.8 to 9.5% into seven main and some minor fractions. By increasing the acrylamide concentration up to 20% nine main fractions could be resolved. In addition to these high molecular weight structural proteins a number of proteins soluble in simple buffer solutions and separable at pH 8.8 in a 15% acrylamide gel are present in the secretion but only to a very small amount.The electrophoretic pattern of the secretory proteins of Chironomus strenzkei, Ch. luridus and Ch. obtusidens are qualitatively the same as the Ch. thummi pattern. Some quantitative differences may exist. In the secretion of Chironomus plumosus at least eleven main fractions were detected in 20% acrylamide gels. A comparison between the number of Balbiani rings of the salivary gland chromosomes and the number of main protein fractions in the salivary gland secretion yielded no direct correlation.The results are discussed in respect to the question wether the major puffs of the gland, the Balbiani rings, encode the major products of the gland, the secretory proteins.Abbreviations used BR Balbiani ring - bis N,N-Methylenebisacrylamide     

The location of repeated DNA sequences in the chromosomes of Chironomus tentans

Polytene chromosomes of Chironomus tentans were hybridized in situ with in vivo labelled nuclear and chromosomal RNA. Nuclear RNA formed hybrids preferentially in five distinct regions considered to contain clustered, repeated DNA sequences. These are the two nucleolar organizer regions, Balbiani ring 1 and 2, and the 5 S RNA genes in region 2A of chromosome II, which together comprised almost 70% of the total number of grains over the complement. The remaining grains were diffusely distributed over the chromosomes. There was a significant difference in the distribution of grains when RNA from different chromosomes was used for hybridization. Chromosome I RNA hybridized preferentially with chromosome I, and chromosome II+III RNA preferentially with chromosome II+III. Some regions within the chromosomes hybridized significantly more chromosomal RNA than other regions. A considerable cross-hybridization of RNA from one particular type of chromosome with the other chromosomes was also found. It is concluded that repeated DNA sequences which hybridize with heterogeneous chromosomal RNA in C. tentans are widely dispersed in the genome. Some of these sequences have a delimited localization, others are dispersed, and some sequences which are transcribed in one particular chromosome are present also in the other chromosomes.