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     

Studies on the catalytic mechanism of H2-forming methylenetetrahydromethanopterin dehydrogenase: para-ortho H2 conversion rates in H2O and D2O

H₂–forming N ⁵,N ¹⁰ –methylenetetrahydromethanopterin dehydrogenase is a novel type of hydrogenase that contains neither nickel nor iron-sulfur clusters. Evidence has been presented that the reaction mechanism catalyzed by the enzyme is very similar to that of the formation of carbocations and H₂ from alkanes under superacidic conditions. We present here further results in support of this mechanism. It was found that the purified enzyme per se did not catalyze the conversion of para H₂ to ortho H₂, a reaction catalyzed by all other hydrogenases known to date. However, it catalyzed the conversion in the presence of the substrate N ⁵,N ¹⁰ –methenyltetrahydromethanopterin (CH≡H₄MPT⁺), indicating that for heterolytic cleavage of H₂ the enzyme-CH≡H₄MPT⁺ complex is required. In D₂O, the formation of HD and D₂ from H₂ rather than a para–ortho H₂ conversion was observed, indicating that after heterolytic cleavage of H₂ the dissociation of the proton from the enzyme-substrate complex is fast relative to the re-formation of free H₂.     

Rp-phosphorothioate modifications in RNase P RNA that interfere with tRNA binding.

We have used Rp-phosphorothioate modifications and a binding interference assay to analyse the role of phosphate oxygens in tRNA recognition by Escherichia coli ribonuclease P (RNase P) RNA. Total (100%) Rp-phosphorothioate modification at A, C or G positions of RNase P RNA strongly impaired tRNA binding and pre-tRNA processing, while effects were less pronounced at U positions. Partially modified E. coli RNase P RNAs were separated into tRNA binding and non-binding fractions by gel retardation. Rp-phosphorothioate modifications that interfered with tRNA binding were found 5' of nucleotides A67, G68, U69, C70, C71, G72, A130, A132, A248, A249, G300, A317, A330, A352, C353 and C354. Manganese rescue at positions U69, C70, A130 and A132 identified, for the first time, sites of direct metal ion coordination in RNase P RNA. Most sites of interference are at strongly conserved nucleotides and nine reside within a long-range base-pairing interaction present in all known RNase P RNAs. In contrast to RNase P RNA, 100% Rp-phosphorothioate substitutions in tRNA showed only moderate effects on binding to RNase P RNAs from E. coli, Bacillus subtilis and Chromatium vinosum, suggesting that pro-Rp phosphate oxygens of mature tRNA contribute relatively little to the formation of the tRNA-RNase P RNA complex.     

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.     

Biochemical and immunocytochemical characterization of monoclonal antibody TOP 35 raised against purified tonoplast from cress root

The vacuolar membrane, the tonoplast, is a proteinrich membranehitherto only few proteins in it have been identified. As anapproach for the identification of tonoplast proteins by monoclonalantibodies (MABs), purified tonoplast from cress roots (Lepidiumsativum L.) were used for immunization and plasma membranesas a control membrane to test the absence of antigen. The MABTOP 35 identified a glycoprotein of about 35 kDa in purifiedtonoplast of cress roots. Triton X-114 phase separation showedthat it was a hydrophobic integral membrane protein. In immunocytochemistrythe MAB TOP 35 strongly labelled the vacuolar membrane. Theabsence of cell wall or plasma membrane labelling by TOP 35indicates a distinct biosynthetic pathway of this protein tothe vacuolar membrane in plants. Key words: Immnocytochemistry, Lepidium sativum, monoclonal antibody, secretion, vacuole     

Recent approaches to probe functional groups in ribonuclease P RNA by modification interference

Modification interference is a powerful method to identify important functional groups in RNA molecules. We review here recent developments of techniques to screen for chemical modifications that interfere with (i) binding of(pre-)tRNA to bacterial RNase P RNA or (ii) pre-tRNA cleavage by this ribozyme. For example, two studies have analyzed positions at which a substitution of sulfur for thepro-Rp oxygen affects tRNA binding [1] or catalysis [2]. The results emphasize the functional key role of a central core element present in all known RNase P RNA subunits. The four sulfur substitutions identified in one study [2] to inhibit the catalytic step also interfered with binding of tRNA toE. coli RNase P RNA [1]. This suggests that losses in binding energy due to the modification at these positions affect the enzyme-substrate and the enzyme-transition state complex. In addition, the two studies have revealed, for the first time, sites of direct metal ion coordination in RNase P RNA. The potentials, limitations and interpretational ambiguities of modification interference experiments as well as factors influencing their outcome are discussed.Abbreviations nt nucleotide(s) - PAGE polyacrylamide gel electrophoresis     

The ant’s path integration system: a neural architecture

 A model is developed by which path integration as observed in many animal species could be implemented neurobiologically. The proposed architecture is able to describe the navigation behaviour of Cataglyphis ants, and that of other social insects, at the level of interacting neurons. The basic idea of this architecture is the concept of activity patterns travelling along neural chains. Although experimental evidence has yet to be provided, this concept seems biologically plausible and not limited to the navigation problem. Neural chains are able to represent variables by activity patterns with high accuracy and temporal stability. Moreover, they are able to integrate incremental signals with high precision. Cyclical chains of neurons show superior performance as soon as cyclical variables are to be represented and integrated. Finally, representation of cyclical variables by travelling activity peaks allows simple approximations of goniometric functions as they are used in path integration systems. Received: 15 November 1994/Accepted in revised form: 30 May 1995