Modification of the microtubule-binding and ATPase activities of kinesin by N-ethylmaleimide (NEM) suggests a role for sulfhydryls in fast axonal transport

N-Ethylmaleimide, an agent which alkylates free sulfhydryls in proteins, has been used to probe the role of sulfhydryls in kinesin, a motor protein for the movement of membrane-bounded organelles in fast axonal transport. When squid axoplasm is perfused with concentrations of NEM higher than 0.5 mM, organelle movements in both the anterograde and retrograde directions cease, and the vesicles remain attached to microtubules. Incubation of highly purified bovine brain kinesin with similar concentrations of NEM modifies the enzyme's microtubule-stimulated ATPase activity and promotes the binding of kinesin to microtubules in the presence of ATP. These results suggest that alkylation of sulfhydryls on kinesin alters the conformation of the protein in a manner that profoundly affects its interactions with ATP and microtubules. The NEM-sensitive sulfhydryls, therefore, may provide a valuable tool for the dissection of functional domains of the kinesin molecule and for understanding the mechanochemical cycle of this enzyme.     

DoesAgapetus fuscipes cultivate algae in its case?

The presence of algae within the cases ofAgapetus fuscipes was investigated. Cases recognised as dirty or clean with the naked eye had more and less algal growth, respectively. Larvae in the former survived significantly longer when starved in the laboratory. It is suggested that the presence of algae within the cases would be of ecological advantage during periods of flood.     

Die Verbreitung des Weidensperlings (Passer hispaniolensis) in Marokko

Zusammenfassung In Marokko fällt die südliche Verbreitungsgrenze des Weidensperlings wahrscheinlich mit dem Nordrand des Antiatlas zusammen. Aus den Oasen der ehemaligen Spanischen Sahara liegen keine Beobachtungen vor. Aus dem Raum Oujda sind die östlichsten Populationen, die ständig zwischen Marokko und Algerien migrieren, bekannt. Landnutzung und Klima prägen entscheidend die Dispersion des Weidensperlings. Als euryöke Art ist er in der Lage, das reichhaltige Angebot an Schlaf- und Brutplätzen sowie an Nahrung und Wasser in den ackerbaulichen Nutzflächen zu verwerten. Auffallend ist, daß die Hauptverbreitungszonen mit den großen ackerbaulichen Nutzflächen zusammenfallen. Während die agrarischen Nutzflächen sich in den letzten Jahrzehnten im Zuge der Modernisierung der Landwirtschaft rapide änderten, und das erklärte Ziel für das Jahr 2000 in einer bewässerten Fläche von einer Million Hektar besteht, gingen die ursprünglichen Habitate des Weidensperlings, wie die Bereiche der mauretanischen Wüstensteppengebiete, drastisch zurück. Ferner konnte im Raum Marrakech eine Abnahme der Niederschläge beobachtet werden, die das für die Weidensperlinge verfügbare Nahrungsangebot entscheidend beeinflußt und somit die Populationsdynamik steuert.

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On the distribution of the Spanish Sparrow (Passer hispaniolensis) in Morocco

Summary In Morocco, the southernmost border of the distribution of the Spanish Sparrow coincides probably with the North-Antiatlas. From the oasis of the former Spanish Sahara don't exist any observations. In the region of Oujda the easternmost populations are found which are migrating permanently between Morocco and Algeria. The euryoecous species is able to use a high variability of different roosts, breeding sites, resources of food and water in the agricultural areas. A high overlap of the main distribution areas with the large agricultural regions is obvious. While the cultivated areas have been changed heavily during the modernisation periode of the Moroccan agriculture the original habitats of the Spanish Sparrow (i. e. the parts in the Mauretanian desert-steppe regions) disappeared dramatically. The goal of the year 2000 lies in an irrigated scheme of 1.000.000 ha. Moreover, a decrease of the precipitation in the region of Marrakech was observed, which has a great influence on the food available for the species and which therefore controls the population dynamics.

     

Double-stranded RNA unwinding and modifying activity is detected ubiquitously in primary tissues and cell lines.

A double-stranded RNA unwinding and modifying activity was found to be present in a wide range of tissues and cell types. The level of activity did not vary significantly with respect to the state of cell differentiation, cell cycle, or transformation. Thus, the unwinding and modifying activity, localized in the nucleus in somatic cells and capable of converting many adenosine residues to inosine, appears to be one of the housekeeping genes.     

Correlation of spinule dynamics and plasticity of the horizontal cell spectral response in cyprinid fish retina: quantitative analysis

Summary A negative feedback interaction between luminosity type horizonatal cells (HCs) and green-sensitive cones generates the long-wavelength-sensitive depolarizing response in biphasic chromaticity type HCs. This interaction is suppressed in the dark and is potentiated by light adaptation of the retina. HCs are morphologically plastic; during light adaptation, their dendritic terminals within cone pedicles extend, giving rise to spinules. This paper examines whether there is a quantitative correlation between the time course of light-dependent formation of the spinules and enhancement of the feedback interaction. The strength of the feedback interaction in isolated retinac of the roach was determined as the neutral wavelength at which reversal of spectral response polarity occurred in biphasic HCs. A good correlation was found between the neutral wavelength and the spinule/ribbon ratios of retinae. Biphasic HCs were intracellularly stained with horseradish peroxidase and the correlative ultrastructure of the contacted pedicles was examined. Neutral wavelength was found to be correlated with the spinule number, weighted according to the number of synaptic contacts mediating feed-forward transmission. The latter was estimated from the total number of labelled C_b/H2 HC processes (central and lateral) at synaptic triads. A model in which spinules mediate the negative feedback interaction of HCs in the retina of cyprinid fish is presented.     

Respiratory pathways in Agaricus bisporus and Scytalidium thermophilum

Abstract The respiratory pathways of Agaricus bisporus and Scytalidium thermophilum were studied. A. bisporus appeared to possess both a cyanide-sensitive and a cyanide-insensitive respiration while in S. thermophilum the cyande-insensitive respiration was absent. Growth experiments showed the ecological advantage for A. bisporus under conditions where cytochrome mediated respiration is inhibited.