Analyses of dose-response curves to compare the antimicrobial activity of model cationic alpha-helical peptides highlights the necessity for a minimum of two activity parameters

To assess and compare different model Leu-Lys-containing cationic alpha-helical peptides, their antimicrobial activities were tested against Escherichia coli as target organism over a broad peptide concentration range. The natural cationic alpha-helical peptides magainin 2 and PGLa and the cyclic cationic peptide gramicidin S were also tested between comparison. The dose-response curves differed widely for these peptides, making it difficult to rank them into an activity order over the whole concentration range. We therefore compared five different inhibition parameters from dose-response curves: IC(min) (lowest concentration leading to growth inhibition), IC(50) (concentration that gives 50% growth inhibition), IC(max) (related to minimum inhibition concentration and minimum bactericidal concentration), inhibition concentration factor (IC(F); describing the increase in concentration of the peptide between minimum and maximum inhibition), and activity slope (A(S); related to the Hill coefficient). We found that these parameters were covariant: two of them sufficed to characterize the dose dependence and hence the activity of the peptides. This was corroborated by showing that the dose dependences followed the Hill equation, with a small, constant aberration. We propose that the activity of antimicrobial peptides can readily be characterized by both IC(50) and IC(F) (or A(S)) rather than by a single parameter and discuss how this may relate to investigations into their mechanisms of action.     

The Drug Diazaborine Blocks Ribosome Biogenesis by Inhibiting the AAA-ATPase Drg1

The drug diazaborine is the only known inhibitor of ribosome biogenesis and specifically blocks large subunit formation in eukaryotic cells. However, the target of this drug and the mechanism of inhibition were unknown. Here we identify the AAA-ATPase Drg1 as a target of diazaborine. Inhibitor binding into the second AAA domain of Drg1 requires ATP loading and results in inhibition of ATP hydrolysis in this site. As a consequence the physiological activity of Drg1, i.e. the release of Rlp24 from pre-60S particles, is blocked, and further progression of cytoplasmic preribosome maturation is prevented. Our results identify the first target of an inhibitor of ribosome biogenesis and provide the mechanism of inhibition of a key step in large ribosomal subunit formation.     

Ultrastructure of the y-organs of Cancer antennarius in normal and de-eyestalked crabs

The paired Y-organs of crustaceans control the molting process. In males of C. antennarius, these glands are opalescent, lobulated, epithelioid structures embedded in brown fatty tissue. Cells in the periphery extend processes to the connective tissue capsule, an arrangement that suggests increased surface area for metabolic exchange. The processes contain mitochondria and are tipped distally with electron dense material. The cytoplasm, scarce relative to nuclear volume, contains vesicles, polymorphic mitochondria with tubular cristae, and numerous free ribosomes, but little in way of smooth or rough endoplasmic reticulum or Golgi complexes. Progressing from intermolt to the premolt stage, mitochondria, as well as vesicles, and electron-dense particles in peripheral processes increase somewhat in number. Also, heterochromatin masses concentrate adjacent to the nuclear envelope. Eyestalk removal, which induces premolt stages in some species, did not produce consistent change in Y-organ substructure in C. antennarius. Although evidence is accumulating that Y-organs secrete a steroid molting hormone during late intermolt-premolt, the substructure of the glands exhibits neither (a) striking changes with the molt cycle, nor (b) all the characteristics typical of vertebrate steroid hormone synthesizing glands. Nevertheless, the structural features, respectively, are consistent with biochemical evidence that Y-organs (a) rapidly take up and convert sterol precursor and secrete a product without its accumulation or change in total sterol pool size, and (b) apparently cannot synthesize the sterol precursor. Y-organ cytology closely resembles that of some vertebrate steroid hormone secreting glands in which this synthetic capacity is minimal.     

The Use of Carbon and Carmine Particles in Cell Fusion Experiments to Distinguish Hybrids from Parental Cells

The phagocytosis of inert particles, a long-known in vivo phenomenon among cells of the reticuloendothelial system, has more recently been found to be a widespread capability of cells in vitro (Gropp 1963) and can be utilized as a marking system when colored particles are employed. Carbon particles (black) were used by Stoker (1964) as cellular markers and later carmine particles (red) were used as markers in cell transformation studies (Stoker 1967; Rabinowitz and Sachs 1968).     

An enzymic synthesis of purine d-Arabinonucleosides

A method is described for the synthesis of purine d-arabinonucleosides that uses purine bases and 2,2′-anhydro-(1-β-d-arabinofuranosylcytosine), AraC-an, as the starting materials. AraC-an was chosen as the precursor to the d-arabinosyl donor, because it is more readily available than any of the products that may be sequentially derived from it, namely, 1-β-d-arabinofuranosylcytosine (AraC), 1-β-d-arabinofuranosyluracil (AraU), and α-d-arabinofuranosyl-1-phosphate (Araf 1-P), a d-arabinofuranosyl donor. Four reactions were involved in the overall process; (a) AraC-an was nonenzymically hydrolyzed at alkaline pH to AraC which was then (b) deaminated by cytidine deaminase to AraU, a nucleoside, (c) phosphorylyzed by uridine phosphorylase to Araf 1-P, and (d) this ester caused to react with a purine base to afford a purine d-arabinonucleoside, the reaction being catalyzed by purine nucleoside phosphorylase. All four reactions occurred in situ, the first and second being performed sequentially, whereas the third and fourth were combined in a single step. The three enzyme catalysts were purified from Escherichia coli. The efficiency of the method is exemplified by the synthesis of the d-arabinonucleosides of 2,6-diaminopurine and adenine; the overall yields, based on AraC-an, were 60 and 80%, respectively.     

Staining yeast cells for electron microscopy by growth in copper-containing nutrient broth

Copper attaches to the nucleoli and the chromosomes of yeast cells. Lindegren and Zink (1969) showed that lipolated mitochondria contain fat and inferred that fat was an energy source. The present study shows that fat is present in the nucleolus and fat is inferred to be an energy source for nucleolar metabolism. The extrusion of nucleoprotein from the nucleolus into the cytoplasm is demonstrated for the first time by electron microscopy. The copper-stained chromosomes are about 90 å in diameter and tightly packed in the nuclear vacuole.     

Oxidative detoxication of thallium in the yeast mitochondria

When yeast cells are grown in thallium-containing broth, the thallium ion is oxidized in the mitochondria to Tl₂O₃. This oxide is subsequently discharged from the mitochondria and finally excreted from the protoplast.     

Mikrobiologische Charakterisierung einiger natürlicher und kultivierter Standorte in drei verschiedenen ökologischen Regionen Chiles

Zusammenfassung Es wurden quantitative Untersuchungen über den jahreszeitlichen Wechsel des Mikrobenbesatzes verschiedener natürlicher und kultivierter B?den in drei verschiedenen ?kologischen Klimabereichen Chiles durchgeführt. Der Massenwechsel der Mikroorganismen der B?den im Steppenklima des Norte Chico sowie derjenigen im sommertrockenen Zentralchile wies eine eingipflige Kurve auf. Das Maximum der Mikrobenaktivit?t wurde w?hrend der Regenzeit beobachtet. Die B?den im konstant feuchten Südchile waren das ganze Jahr hindurch stark belebt. W?hrend der besonders feuchten Wintermonate wurde in diesem Teil Chiles allgemein eine Zunahme der anaeroben Organismen beobachtet. Besonders auffallend war dies in den Gleyb?den, wo diese Organismengruppe w?hrend dieser Jahreszeit vorherrschend war. Die hohen winterlichen Niederschlagsmengen hatten vor allem in der Selva Valdiviana eine Versauerung des Bodens zur Folge. Der Abfall des pH-Wertes hatte an diesem Standort eine sprunghafte Zunahme des Pilzbesatztes zur Folge. Es wurde auf den Einflu? der Be- bzw. Entw?sserung der B?den auf den Mikrobenbesatz hingewiesen. Die Aufforstung mit Pinus insigne hatte im Süden Chiles eine Versauerung des Bodens und damit verbunden eine Abnahme des Mikrobenbesatzes zur Folge. Vergliechen mit einem natürlichen Wald, wies der Pinuswald ein viel engeres Verh?ltnis Bakterien: Pilze auf. Die Pilzflora der einzelnen ?kologischen Klimabereiche war sehr verschieden. In den sommertrockenen Gebieten herrschten verschiedene Vertreter der GattungAspergillus vor. In dem konstant feuchten Süden Chiles fehlten diese. Hier wurden verschiedene Mucorineen, wie z.B.Circinella undZygorhynchus isoliert, die wiederum in den Trockengebieten fehlten.

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Summary Quantitative investigations were made of the seasonal variation of microbial life in several natural and cultivated soils in three different climatic zones of Chile. In the soils of the steppe climate in the Norte Chico as well as in the soils of Central Chile with its temperate, summer-dry climate the maximum of microbial life was observed during the rainy season. The soils in the constant humid and temperate south of Chile showed a remarkable number of micro-organisms all the year over. During the most humid months in wintertime an increase of the number of the anaerobionts in all sites of this part of Chile was observed. In the gley-soils in which the anaerobionts were dominating during the winterseason, this was especially remarkable. The high amount of precipitation during wintertime caused an acidification of the soils particularly of the brown earth under Selva Valdiviana. The decrease of the pH value in this soil caused a sudden increase of the numbers of fungi. The influence of irrigation and drainage on the number of micro-organisms was demonstrated. The afforestation withPinus insigne caused in the south of Chile an acidification of the soil and at the same time a decrease of the microbial numbers. The relation between bacteria and fungi in the Pinus forest was closer than in the naturally grown forest. In the various ecological zones of climate the fungous flora was very different. In the summer-dry regions the genusAspergillus was dominant. This genus was not found in the constant humid south. From these soils different Mucorinees, for exampleCircinella simplex andZygorhynchus heterogamus, were isolated. These fungi were not observed in the dry regions.