Activation by actin of ATPase activity of chemically modified gizzard myosin without phosphorylation.

The ATPase activity of myosin from chicken gizzard measured in the presence of either Mg²⁺ or Ca²⁺ is increased in the absence of dithiothreitol or upon reaction with Cu²⁺, o-iodosobenzoate, or N-ethylmaleimide. Iodosobenzoate or Cu²⁺ produce no change in K⁺(EDTA)-ATPase while N-ethylmaleimide produces a decrease. These treatments also make the actin-activated ATPase insensitive to Ca²⁺ when assayed in the presence of tropomyosin and a partially purified myosin light chain kinase. Phosphorylation of N-ethylmaleimide modified myosin remains dependent on Ca²⁺ and therefore appears not to be required for activation by actin of the ATPase activity of modified myosin.     

Chymotryptic heavy meromyosin from gizzard myosin: a proteolytic fragment with the regulatory properties of the intact myosin.

Arginine deiminase (EC 3.5.3.6) from $\text{Mycoplasma}\text{arthritidis}$ is a dimeric enzyme. Velocity centrifugation in 6 M guanidine HCl and peptide mapping of the BrCN fragments suggest that the subunits are identical. The reaction of one out of four sulfhydryl groups with 0.3 mM 5,5′-dithiobis-(2-nitrobenzoic acid) has a half-life of about 30 min in 2 M guanidine HCl at 15°, pH 8. The enzyme is irreversibly inhibited by 1 mM formamidinium ion within 1 min. Inactivation by this affinity label is resolvable into two concurrent first-order reactions in the presence of guanidinium ion; the fraction of enzyme which reacts at the faster rate is about 50%. These results are interpreted as evidence for two catalytic subunits which differ in conformation.     

Cytological and cytogenetical studies on brain tumors

Summary Twelve out of 88 cytogenetically examined meningiomas of female patients showed, in addition to the typical loss of a chromosome 22, a loss of 1 or more chromosomes of group C. Among them 8 tumors had less than 8% cells with Barr-body-like particles, whereas in one tumor 12% and in 3 others over 20% Barr bodies were found, which, based on control studies, were classified as sex-chromatin negative, partly positive, and positive, respectively. In one case the loss of an X chromosome was verified by Giemsa banding.In 6 out of 24 meningiomas of male origin, the chromosoma. morphology and association pattern strongly indicated that besides the loss of a chromosome 22, the Y chromosome was also missing. Moreover, the loss of the male sex chromosome could be ascertained in 4 tumors by the conspicuous absence of Y fluorescence in interphase nuclei and in metaphase plates after fluorescence staining.The findings are discussed in connection with the gonosomal loss in other human tumors and in old age.

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Zusammenfassung Unter 88 cytogenetisch untersuchten Meningeomen von Frauen wurden 12 Tumoren gefunden, bei denen außer dem für Meningeome typischen Verlust eines Chromosoms 22 auch ein oder mehrere Chromosomen der C-Gruppe verlorengegangen waren. Bei 8 dieser Tumoren konnte in Gewebekulturpräparaten nur in weniger als 8% der untersuchten Zellen Barr-body-ähnliche Kernstrukturen nachgewiesen werden, bei einem Tumor fanden sich 12% und bei 3 über 20% Barr-bodies. Auf Grund von Vergleichsuntersuchungen wurden 8 Tumoren als geschlechtschromatinnegativ, 1 Tumor als teilweise positiv und die übrigen 3 als eindeutig positiv eingestuft. Bei einem Meningeom konnte das Fehlen eines X-Chromosoms direkt mit der Giemsa-Bandentechnik nachgewiesen werden.Bei 6 von 24 Meningeomen männlicher Herkunft konnte auf Grund der Chromosomenmorphologie und des Assoziationsverhaltens sehr wahrscheinlich gemacht werden, daß außer dem Chromosom 22 auch das Y-Chromosom verlorengegangen war. Bei 4 dieser Tumoren konnte eine Fluorescenzfärbung durchgeführt werden, wobei das Fehlen einer Y-Fluorescenz in Interphasezellen und Metaphaseplatten nachweisbar war.Diese Befunde werden im Zusammenhang mit dem Geschlechtschromosomenverlust bei anderen menschlichen Tumoren und im hohen Lebensalter diskutiert.

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Supported by the Deutsche Forschungsgemeinschaft (SFB 51 E 12).

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Parts of this work are included in the doctoral thesis (M.D.) of H.S. at the University of Munich, Germany.     

Lipolysis drives expression of the constitutively active receptor GPR3 to induce adipose thermogenesis

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The contribution of TRPV4-mediated calcium signaling to calcium homeostasis in endothelial cells

A large variety of cation transport systems are involved in the regulation of calcium homeostasis in endothelial cells. The focus of the present study is to determine the contribution of nonselective cation channels from the TRP (transient receptor potential) family to cellular calcium homeostasis of porcine aortic endothelial cells (PAEC). One member of the TRPV (vanniloid) subfamily, TRPV4, has previously been shown to be involved in cation transport induced by a large variety of stimulations including osmolarity, temperature, mechanical stress, and phosphorylation. Here, we demonstrate the existence of several TRP proteins, including TRPV4, in PAEC using RT-PCR. To test whether this channel is functional, we performed FURA-2 calcium measurements and whole-cell patch-clamp experiments. We observed the induction of large calcium signals following mechanical stress, altered extracellular temperature, and the selective TRPV4 activator 4-alpha -PDD. These effects were diminished in the presence of the TRPV4 inhibitor miconazole, suggesting the involvement of this channel in mediating endothelial calcium signals. The large amounts of transported calcium and the short signaling ways suggest a potentially important role of this channel in many physiological processes.     

Beta‐diversity in temperate and tropical forests reflects dissimilar mechanisms of community assembly

Site‐to‐site variation in species composition (β‐diversity) generally increases from low‐ to high‐diversity regions. Although biogeographical differences in community assembly mechanisms may explain this pattern, random sampling effects can create this pattern through differences in regional species pools. Here, we compared assembly mechanisms between spatially extensive networks of temperate and tropical forest plots with highly divergent species pools (46 vs. 607 species). After controlling for sampling effects, β‐diversity of woody plants was similar and higher than expected by chance in both forests, reflecting strong intraspecific aggregation. However, different mechanisms appeared to explain aggregation in the two forests. In the temperate forest, aggregation reflected stronger environmental correlations, suggesting an important role for species‐sorting (e.g. environmental filtering) processes, whereas in the tropics, aggregation reflected stronger spatial correlations, more likely reflecting dispersal limitation. We suggest that biogeographical differences in the relative importance of different community assembly mechanisms contribute to these striking gradients in global biodiversity.     

Laccase versus Laccase-Like Multi-Copper Oxidase: A Comparative Study of Similar Enzymes with Diverse Substrate Spectra

Laccases (EC 1.10.3.2) are multi-copper oxidases that catalyse the one-electron oxidation of a broad range of compounds including substituted phenols, arylamines and aromatic thiols to the corresponding radicals. Owing to their broad substrate range, copper-containing laccases are versatile biocatalysts, capable of oxidizing numerous natural and non-natural industry-relevant compounds, with water as the sole by-product. In the present study, 10 of the 11 multi-copper oxidases, hitherto considered to be laccases, from fungi, plant and bacterial origin were compared. A substrate screen of 91 natural and non-natural compounds was recorded and revealed a fairly broad but distinctive substrate spectrum amongst the enzymes. Even though the enzymes share conserved active site residues we found that the substrate ranges of the individual enzymes varied considerably. The EC classification is based on the type of chemical reaction performed and the actual name of the enzyme often refers to the physiological substrate. However, for the enzymes studied in this work such classification is not feasible, even more so as their prime substrates or natural functions are mainly unknown. The classification of multi-copper oxidases assigned as laccases remains a challenge. For the sake of simplicity we propose to introduce the term “laccase-like multi-copper oxidase” (LMCO) in addition to the term laccase that we use exclusively for the enzyme originally identified from the sap of the lacquer tree Rhus vernicifera.