Vergleichende Untersuchungen zum Tryptophanstoffwechsel in Leberzellfraktionen bei Wirbeltieren

Zusammenfassung Der Tryptophanabbau in der Leber von Ratte (Mus rattus L. domest.), Kaninchen (Oryctolagus cuniculus L. domest.), Hahn (Gallus bankiva domest.), Taube (Columba livia L.), Frosch (Rana temporaria L.) und Fisch (Leuciscus rutilus L.) wurde in qualitativer und quantitativer Hinsicht untersucht. Es wurden die Aktivitäten des TryptophanPeroxydase-Systems, der Kynureninase und der Kynurenin-Transaminase bestimmt, sowie ihre Verteilung auf die einzelnen Zellfraktionen. Die Papierchromatographie wurde zur qualitativen Analyse der entstandenen Stoffwechselprodukte herangezogen.Außer beim Hahn wird Tryptophan praktisch ausschließlich über Kynurenin zu Kynurensäure und Anthranilsäure abgebaut. Die Verteilung der Enzyme auf die Zellfraktionen entspricht der vom Säugetier bekannten, die Aktivitäten liegen in der gleichen Größenordnung.Beim Hahn wird Kynurenin auch von Mitochondrien und Kernfraktion gebildet. Die Kynureninbildung im Cytoplasma wird durch Kombination von Cytoplasma + Mikrosomen oder Cytoplasma + Mitochondrien auf das Mehrfache erhöht. Auch scheint beim Hahn neben der Kynureninbildung noch ein zweiter Mechanismus des Tryptophanabbaus vorhanden zu sein. Durch Cyclophorasesystem wird aus Tryptophan eine gelbe Substanz gebildet, die aber nicht identifiziert werden konnte. Eine Kynurensäurebildung wird beim Hahn nicht gefunden, was im Einklang steht mit der Tatsache, daß er keine Kynurensäure ausscheidet.Fütterungsversuche an Ratten ergaben, daß bei tryptophanarmer Nahrung die Aktivität des Tryptophan-Peroxydase-Systems deutlich unter die Normalwerte absinkt, während Kynureninase und Kynurenintransaminase nicht beeinflußt werden.     

Characterization of the T, L, I, S, M and P cell surface (immobilization) antigens of Tetrahymena thermophila: molecular weights, isoforms, and cross-reactivity of antisera.

In the ciliate protist Tetrahymena thermophila the L, H, T, I, S, M and P cell surface proteins (immobilization antigens) are expressed under different conditions of temperature (L, H, T), culture media (I, S), and mutant genotype (M, P). Immunoblot and autoradiographic studies using antisera to purified protein show that the molecular weights of these proteins range from 25,000 to 59,000. The H, T, S, M and P antigens are recognized as single polypeptides, whereas L, I, and one allelic form of T each appear to consist of a family of polypeptides. Although antisera are specific in immobilization and immunofluorescence assays of surface protein in living cells, cross-reactivity is seen with denatured protein on immunoblots. It is hypothesized that the surface protein genes are organized into families of evolutionarily related isoloci.     

Size-fractionated biomass, photosynthesis and dark CO2 fixation in a tropical oceanic environment

This study examines the spatial distribution and size structureof phytoplankton biomass and productivity in relation to thevertical structrure of the Andaman Sea (northeastern IndianOcean). This region was characterized by low concentrationsof nutrients and high levels of insolation. Nitrogen availabilityappeared to control overall productivity with nitrate-based‘new’ production accounting for 8–24% of thetotal primary production. Euphotic column chlorophyll (chl a)averaged 52.5 mg m^–2 of which a major portion was locatedas a subsurface chl a maximum (SCM) at     

Clinical ethics and nursing: "yes" to caring, but "no" to a female ethics of care

According to a contemporary school of thought there is a specific female approach to ethics which is based not on abstract "male" ethical principles or rules, but on "care". Nurses have taken a keen interest in these female approaches to ethics. Drawing on the views expounded by Carol Gilligan and Nel Noddings, nurses claim that a female "ethics of care" better captures their moral experiences than a traditional male "ethics of justice". This paper argues that "care" is best understood in a dispositional sense, that is, as sensitivity and responsiveness to the particularities of a situation and the needs of "concrete" others. While "care", in this sense, is necessary for ethics, it is not sufficient. Ethics needs "justice" as well as "care". If women and nurses excessively devalue principles and norms, they will be left without the theoretical tools to condemn some actions or practices, and to defend others. They will, like generations of nurses before them, be condemned to silence.     

A family of modular type mannuronan C-5-epimerase genes controls alginate structure in Azotobacter vinelandii

The ToxR protein is a transmembrane protein that regulates the expression of several virulence factors of Vibrio cholerae. Previous analysis of fusion proteins between ToxR and alkaline phosphatase (ToxR-PhoA) suggested that ToxR was active as a dimer. In order to determine whether dimerization of the ToxR periplasmic domain was essential for activity, this domain was replaced by monomeric and dimeric protein domains. Surprisingly, PhoA (dimeric), β-lactamase (monomeric, ToxR–Bla), or the leucine zipper of GCN4 (dimeric, ToxR-GCN4-M) could substitute functionally for the ToxR periplasmic domain. ToxR-GCN4 fusion proteins, in which the ToxR trans-membrane domain was eliminated (ToxR-GCN4-C), were inactive, but an additional fusion protein that contained a heterologous membrane-spanning domain retained activity. Strains containing each of these ToxR fusion proteins were analysed for in vivo colonization properties and response to in vitro growth conditions that are known to affect expression of the ToxR regulon. Strains containing ToxR-GCN4-M and ToxR-Bla responded like wild-type strains to in vitro growth conditions. In the infant-mouse colonization model, strains containing ToxR fusion proteins were all deficient in colonization relative to strains containing wild-type ToxR, and strains containing monomeric ToxR-Bla were most severely outcompeted. These results suggest that, under in vitro conditions, ToxR does not require a dimerized periplasmic domain, but that, under in vivo conditions, the correct conformation of the ToxR periplasmic domain may be more important for function.     

Coaction of three factors controlling chlorophyll and anthocyanin synthesis

In a three-factor analysis the rate of chlorophyll a (Chl) accumulation in excised mustard cotyledons was studied as a function of kinetin, light (operating through phytochrome, P _fr) and an excision factor. It was found that the three factors operate additively provided that the P _fr level is high enough. When the P _fr level is below approximately 1 per cent (<0.01) the effectiveness of the excision factor decreases while the effect of kinetin remains additive. The observed additivity is explained by a model where the three factors operate independently through a common intermediate (presumably 5-aminolevulinate) in the biosynthetic chain leading to Chl. With regard to the coaction of the excision factor and phytochrome it is concluded that the production of the excision factor requires the operation of phytochrome (even though saturated at a low P _fr level) while the action of the excision factor is independent of phytochrome. This conclusion was confirmed by experiments in which the rate of light-mediated anthocyanin synthesis was measured in excised mustard cotyledons. The effect of excision in the case of anthocyanin formation differs kinetically from the effect of excision on Chl formation.Abbreviations Chl chlorophyll(ide) a - P _fr far-red absorbing form of phytochrome - P _fr/P _tot ratio at photoequilibrium - RL red light - FR far-red light - GL green light - RG9 light long wavelength far-red light - WL white light