Showing papers by "University of Tübingen published in 1986"

Fengycin-a novel antifungal lipopeptide antibiotic produced by bacillus subtilis f-29-3

Abstract: Fengycin is an antifungal lipopeptide complex produced by Bacillus subtilis strain F-29-3. It inhibits filamentous fungi but is ineffective against yeast and bacteria. The inhibition is antagonized by sterols, phospholipids and oleic acid, whereas two other unsaturated fatty acids increase the antifungal effect. Fengycin consists of two main components differing by one amino acid exchange. Fengycin A is composed of 1 D-Ala, 1 L-Ile, 1 L-Pro, 1 D-allo-Thr, 3 L-Glx, 1 D-Tyr, 1 L-Tyr, 1 D-Orn, whereas in fengycin B the D-Ala is replaced by D-Val. The lipid moiety of both analogs is more variable, as fatty acids have been identified as anteiso-pentadecanoic acid (ai-C15), iso-hexadecanoic acid (i-C16), n-hexadecanoic acid (n-C16), and there is evidence for further saturated and unsaturated residues up to C18.

Sufficient subalgebras and the relative entropy of states of a von Neumann algebra

Abstract: A subalgebraM 0 of a von Neumann algebraM is called weakly sufficient with respect to a pair (φ,ω) of states if the relative entropy of φ and ω coincides with the relative entropy of their restrictions toM 0. The main result says thatM 0 is weakly sufficient for (φ,ω) if and only ifM 0 contains the Radon-Nikodym cocycle [Dφ,Dω] t . Other conditions are formulated in terms of generalized conditional expectations and the relative Hamiltonian.

Epidermin: sequencing of a heterodet tetracyclic 21-peptide amide antibiotic

Abstract: Epidermin is a large peptide antibiotic, which is synthesized in the ribosome via a precursor protein, followed by enzymatic modifications. It was isolated from the culture filtrate of Staphylococcus epidermidis Tu 3298 by adsorption on Amberlite XAD-8. The basic heneicosapeptide amide was chromatographed on Sephadex LH-20 and purified to homogeneity via multiplicative counter-current distributions in one acidic and one neutral system. Tryptic digestion gave the soluble N-terminal fragment epidermin-(1–13)-peptide (P1) and the insoluble C-terminal fragment 2-oxobutyryl-epidermin-(15–21)-peptide amide (P2), each possessing two sulfide ring systems. The heterodetic rings consisted of meso-lanthionine and (2S,3S,6R)-3-methyllanthionine (P1), meso-lanthionine and C-terminally the new amino acid S-(2-aminovinyl)-D-cysteine (P2). The complex sequence was elucidated via a combination of desulfurization with Raney nickel, enzymatic and acidolytic degradations, gas-phase sequencing, fast-atom bombardment and field-desorption mass spectrometry and NMR spectroscopy.

Metabolic products of microorganisms. 234 urdamycins, new angucycline antibiotics from streptomyces fradiae

Abstract: The colored urdamycins A to F, six new angucycline antibiotics produced by Streptomyces fradiae strain Tu 2717, were detected by chemical screening. They are biologically active against Gram-positive bacteria and stem cells of murine L1210 leukemia. The urdamycins are glycosides and differ in their aglycones, which can be liberated by acidic hydrolysis besides the sugars D-olivose and L-rhodinose. The structure of the main compound, urdamycin A, follows from the spectroscopic and chemical data in connection with an X-ray analysis. The aglycone urdamycinone A is identical with aquayamycin. The structures of urdamycin B, E, F and partial structures of urdamycin C and D, will be presented in a subsequent paper. The new term "angucycline/angucyclinone" is used for an increasing group of related antibiotics.

Voltage-dependent channel formation by rods of helical polypeptides.

Abstract: The voltage-dependence of channel formation by alamethicin and its natural analogues can be described by a dipole flip-flop gating model, based on electric field-induced transbilayer orientational movements of single molecules. These field-induced changes in orientation result from the large permanent dipole moment of alamethicin, which adopts α-helical conformation in hydrophobic medium. It was, therefore, supposed that the only structural requirement for voltage-dependent formation of alamethicin-type channels might be a rigid lipophilic helical segment of minimum length. In order to test this hypothesis we synthesized a family of lipophilic polypeptides—Boc-(Ala-Aib-Ala-Aib-Ala) n -OMe,n=1–4—which adopt α-helical conformation forn=2–4 and studied their interaction with planar lipid bilayers. Surprisingly, despite their large difference in chain length, all four polypeptides showed qualitatively similar behavior. At low field strength of the membrane electric field these polypeptides induce a significant, almost voltage-independent increase of the bilayer conductivity. At high field strength, however, a strongly voltage-dependent conductance increase occurs similar to that observed with alamethicin. It results from the opening of a multitude of ion translocating channels within the membrane phase. The steady-state voltage-dependent conductance depends on the 8th–9th power of polypeptide concentration and involves the transfer of 4–5 formal elementary charges. From the power dependences on polypeptide concentration and applied voltage of the time constants in voltage-jump current-relaxation experiments, it is concluded that channels could be formed from preexisting dodecamer aggregates by the simultaneous reorientation of six formal elementary charges. Channels exhibit large conductance values of several nS, which become larger towards shorter polypeptide chain length. A mean channel diameter of 19 A is estimated corresponding roughly to the lumen diameter of a barrel comprised of 10 α-helical staves. Similar to experiments with the N-terminal Boc-derivative of alamethicin we did not observe the burst sequence of nonintegral conductance steps typical of natural (N-terminal Ac-Aib)-alamethicin. Saturation in current/voltage curves as well as current inactivation in voltage-jump current-relaxation experiments are found. This may be understood by assuming that channels are generated as dodecamers but, while reaching the steady state, reduce their size to that of an octamer or nonamer. We conclude that the overall behavior of these synthetic polypeptides is very similar to that of alamethicin. They exhibit the same concentration and voltage-dependences but lack the stabilizing principle of resolved channel states characteristic of alamethicin.

Mycorrhiza of forest trees — structure and function

Abstract: Comprehensive surveys on mycorrhizae have recently been published by Harley and Smith (1983) and Strullu (1985). Harley (1984) has also briefly summarized mycorrhizal associations in general, whilst Moser and Haselwandter (1983) reported on the ecophysiology and Duddridge (1985) on the interface in mycorrhizae of Agaricales. France and Reid (1983) presented a compilation of the current knowledge regarding the nitrogen and carbon physiology of ectomycorrhizae. The main interest of the present paper lies in the interpretation of the morphology and ultrastructure of ectomycorrhizae of forest trees in respect of their function in the uptake and exchange of nutrients. The protectional ability of mycorrhizae is also considered briefly. Recent studies have shown the surprising similarity in the structure of the Hartig net and significant differences in the structure of the mantles of different mycorrhiza-forming fungal species, thus confirming the early report by Mangin (1910). This review article therefore deals firstly with more general aspects, that is the structure and function of the Hartig net in respect to nutrient exchange and transport, and secondly with the more specialized structures of the hyphal mantle, including hyphal strands and rhizomorphs and their function in nutrient uptake and storage. Finally, developmental changes of structure and function and those caused by environmental conditions are discussed.

Glucose repression: a complex regulatory system in yeast.

Abstract: Glucose repression is a complex regulatory system controlling numerous biochemical pathways. The triggering signal for glucose repression of many enzymes is given by hexokinase isoenzyme P11. In addition to glucose repression a glucose derepression system exists. Certain upstream activation sites have been identified for glucose derepression.

Role of the optic lobes in the regulation of the locomotor activity rhythm of Drosophila melanogaster: behavioral analysis of neural mutants.

Abstract: The locomotor activity patterns of the Drosophila melanogaster brain mutants optomotor blind (omb), lobula plateless (lop), minibrain (mnb), small optic lobes (sol), sine oculir (so), and the double mutants mnb;so and sol;so, all of which show reductions in the optic lobes, were investigated and compared with those of the wild-type. In none of the mutants was the number of arrhythmic flies significantly higher than in the wild-type, indicating that the optic lobes are not the sole site of a pacemaker controlling the locomotor activity rhythm. However, these mutations greatly influence the stability of the circadian system, in that the number of flies simultaneously showing two or more circadian components increased as the optic lobe defects became more severe. In flies with the strongest reduction of the optic lobes, two free-running circadian components were found almost exclusively. This suggests a two-oscillator control of the locomotor activity. Eyeless mutants also expressing a neural mutation were entrained by light : dark (LD) cycles, but their activity pattern in LD was changed compared to the wild-type and the eyeless mutant so.

The cross-bridge cycle in muscle. Mechanical, biochemical, and structural studies on single skinned rabbit psoas fibers to characterize cross-bridge kinetics in muscle for correlation with the actomyosin-ATPase in solution.

Abstract: A characteristic and important feature of myocardium is the modulation of tension when stimulated or possibly even when unstimulated. In addition, resistance to stretch and its variation in unstimulated heart muscle is an important factor in myocardial function. These features may occur in some new light when viewed from some recent advances in understanding of cross-bridge action and regulation of muscle. For this reason we give a short review of such advances. Firstly, we summarize some of our earlier results obtained in experiments designed to see whether and to what extent actomyosin ATPase data obtained in solution might apply in muscle. Secondly, we present a recently developed experimental approach to estimate the rate constants that determine the cycling of cross-bridges between weak-binding, ‘non-force-generating’ states and strong-binding, ‘force-generating’ states. The estimated rate constants confirm the prediction of cross-bridge models derived from in vitro studies that the step which is rate-limiting in solution also determines the rate of force-generation in the cross-bridge cycle in muscle. Experiments at various Ca++ concentrations imply that a major mechanism of regulation is the control of the transition from the weak-binding, ‘non-force-generating’ states to the strong-binding, ‘force-generating’ states while the number of activated interaction sites appears unchanged and always at its maximum. This implies that changes in the force-pCa relation cannot be interpreted without detailed analysis of cross-bridge kinetics, and that factors other than Ca++ may have the potential to modulate muscle activity, both in stimulated and unstimulated muscle, by affecting cross-bridge kinetics.

Superior sagittal sinus thrombosis: neuroradiological evaluation and clinical findings.

Abstract: The spectrum of clinical signs in cases of superior sagittal sinus thrombosis includes not only focal neurological deficits, seizures and mental disturbances, but also symptoms which may lead to a diagnosis of pseudotumour cerebri (PTC). In 14 cases of angiographically (or autopsy) proven thrombosis of the superior sagittal or both lateral sinuses, the "empty triangle" sign on contrast CT examination was the most reliable sign, suggesting the diagnosis in 70%. Indirect CT signs (venous infarcts) were observed in all 8 patients with focal neurological signs, but appeared rather delayed in 3 cases. In contrast, patients with "benign" intracranial hypertension or PTC (6 cases) had normal unenhanced scans (4 cases) or showed slight diffuse brain oedema (2 cases). Magnetic resonance imaging was performed in 4 patients with findings suggestive of intravascular coagulation; however, due to the complexity of flow phenomena, further studies employing this new imaging technique will first have to be performed. Thus, angiography remains the best diagnostic tool and should not be delayed if there is a clinical suspicion of thrombosis.

Light and social effects on the free-running circadian activity rhythm in common marmosets (Callithrix jacchus; Primates): social masking, pseudo-splitting, and relative coordination

Abstract: The variability of period of the free-running circadian activity rhythm (CAR) and the degree to which it is affected by social factors was studied in diurnal marmosets (Callithrix jacchus: Primates, Cebidae), kept either singly or in pairs. Under continuous light intensities between 10-1 and 102 lx, the spontaneous period was always shorter than 24h. It varied in relation to the amount of time spent under constant conditions (after-effects). There was some evidence of an effect of light intensity on free-running period, but no clear correlation between the two. Mutual acoustic social contact caused some males to exhibit pseudo-splitting, ascribable to positive social masking, and in many cases also resulted in relative coordination of the free-running CAR. True social entrainment, however, was not produced. The possibility that the latter could occur under some conditions is discussed, as well as the neural pathways that might mediate the observed acoustically induced social effects on the central nervous system pacemaker(s) of the circadian timing system.

Surface acoustic waves in Ni/V superlattices

Abstract: We have measured the surface-acoustic-wave velocities in Ni/V superlattices using both Brillouin scattering and surface-acoustic-wave techniques; the results are in good quantitative agreement. These results confirm earlier reports of phonon-velocity softening in bcc/fcc superlattices and prove that this is a general phenomenon, not a consequence of the measurement method. In addition, we describe in detail the ultrasonic measurement technique which allowed measurements to be performed in thin films.

Pseudocopies of the ATPase α-subunit gene in Oenothera mitochondria are present on different circular molecules

Abstract: The gene coding for the α-subunit of the mitochondrial ATPase was localized in the mitochondrial genome of Oenothera. Several pseudogenes are encoded besides the single intact reading frame. A rearrangement in the initiation codon of the open reading frame has created a pseudogene, where a reading frame continuous with upstream sequences has abolished normal levels of transcription. A second reorganisation 264 bp downstream has created a third locus containing the 5′ portion of the first pseudogene. This latter sequence is located on one of the small circular mitochondrial molecules.

Plaque retention on teeth restored with full-ceramic crowns: a comparative study.

Abstract: Plaque accumulation was determined by using the plaque index of Silness and Loe on 150 crowns in 19 patients. The plaque indices for individual crowns in a quadrant were compared to the average plaque index of the quadrant in which the crowns were inserted (quadrant plaque index = 100%). This comparative study showed that Cerestore full-ceramic crowns have little soft debris retention (32%). Ceramometal crowns (90%), natural teeth (110%), cast gold restorations (148%), and acrylic resin veneer crowns (152%) have increasing plaque retention. The results indicate that ceramics are easily cleaned and exhibit low plaque retention. Increasing the area of ceramic surfaces on restorations decreases plaque retention.

Osmoregulation in eukaryotic algae

Abstract: The cells of marine and halotolerant eukaryotic algae can achieve osmotic balance by ion accumulation mechanisms or by the synthesis and degradation of compatible solutes. The latter mechanism has been extensively studied in Dunaliella tertiolecta, in which the compatible solute glycerol is synthesised and metabolised through the glycerol cycle. Osmoregulation in Poterioochromonas malhamensis by isofloridoside as the compatible solute has a different control mechanism. The results obtained with unicellular algae might lead to strategies for the improvement of salt and water stress resistance in crop plants.

Treatment of murine L1210 lymphoid leukemia and melanoma B16 with lipophilic cytosine arabinoside prodrugs incorporated into unilamellar liposomes.

Abstract: Lipophilic prodrugs of I-beta-D-arabinofuranosyl cytosine (Ara-C), namely N4- and 5'-oleyl-I-beta-D-arabinofuranosyl cytosine (N4-oleyl-ara-C, 5'-oleyl-ara-C) and N4-palmitoyl-I-beta-D-arabinofuranosyl cytosine (N4-palm-ara-C) were incorporated into liposomes of various lipid compositions. The phospholipid vesicles were prepared by controlled dialysis of lipid/prodrug/detergent micelles yielding homogeneous and stable unilamellar liposomes. The liposome size ranged from 70 to 120 nm depending on the lipid composition and the amounts of prodrug incorporated. Depending on the total amount of micellized Ara-C prodrugs, a maximal incorporation rate of 250 micrograms prodrug per mg egg phosphatidylcholine was achieved. The incorporation efficiency was in the range of 85 to 97%. The in vivo antitumor activity of the liposome preparations against L1210 lymphoid leukemia was clearly superior by factors of 2-8 depending on the therapy schedule and route of drug application. The treatment of melanoma B16 with free Ara-C as well as with the prodrug-liposomes exhibit rather weak antitumor activity. Drug application by means of prodrug-liposomes yields equal or higher tumor-inhibitory effects at drug concentrations which were 2-4 times lower than those of free Ara-C. Although drug tolerance and myelosuppression studies with Swiss albino mice revealed that the prodrug-liposomes were 5-10 times more toxic than free Ara-C, a substantial improvement of efficiency could be observed. The incorporation of the ara-C prodrugs into liposomes provides protection against fast degradation and systemic elimination which might be an explanation for the improved antitumor effect of these preparations.

Iron hydroxamate transport of Escherichia coli : Nucleotide sequence of the fhuB gene and identification of the protein

Abstract: The genes fhuA, fhuC and fhuD encode products involved in the transport of ferrichrome into cells of Escherichia coli. The nucleotide sequence of an additional locus contiguous to fhuD and formerly designated fhuB was determined. It contains an open reading frame for a polypeptide that consists of 659 amino acids. Expression of plasmids containing the fhuB region in an in vitro transcription/translation system and in E. coli minicells revealed a polypeptide with an electrophoretic mobility on SDS-polyacrylamide gels extremely dependent on the experimental conditions employed. This property could be explained by the very hydrophobic nature of the protein and it was concluded that the fhuB locus consists of a structural gene that encodes a membrane protein with a molecular weight of 82,181. The fhuB gene is required for all iron transport systems which operate via hydroxamate compounds. The order of the genes in the fhu operon is fhuA fhuC fhuD fhuB, and transcription proceeds from fhuA to fhuB.