Studies on the interaction of tiamulin with the phospholipids in model membranes and with microsomes.

The drug tiamulin interacts with phospholipid membranes mainly in a nonelectrostatic way. At pH-values where the drug possesses a net positive charge only small binding is observed. In the presence of cholesterol tiamulin is excluded from the membranes. The interaction of tiamulin with membranes cannot be explained by a simple partitioning but is governed by structural rearrangements of the lipid phase. At low drug concentrations we observe sigmoidal binding characteristics in the rigid as well as in the fluid state up to a level of about 2-3 mol drug bound per 1000 mol phospholipid. The range in which this cooperative interaction occurs can be compared with the drug concentration in the erythrocyte membrane which protects from hypotonic lysis. Further addition of tiamulin to the rigid membrane leads to fluidization. Saturation of the membranes with tiamulin is completely in parallel to their fluidization. The relevance of the cooperative interaction at low drug concentration and of the subsequent fluidization at elevated concentration for the microsomal membrane is discussed.     

Ultrastructural and autoradiographic observations of hamster cheek pouch epithelium grown in vitro.

Epithelial outgrowths from hamster cheek pouch explants were cultured for varying periods of time up to 22 days. Growth of the epithelial sheets was monitored, employing colcemid for demonstrating mitotic activity and tritiated thymidine for DNA synthesis. Mitoses and thymidine uptake were observed among epithelial outgrowths at a considerable distance form the original explant. The epithelial nature of the growing cell sheets was confirmed, employing electron microscopic techniques. The cells exhibited the presence of tonofilaments, desmosomes, ribosomes, Golgi, mitochondria, and rough endoplasmic reticulum. The cultured explants were treated with cyclic nucleotides in order to investigate their modulatory effects on epithelial cell differentiation. Dibutyryl cAMP induced marked mitotic inhibition (46.3%) in our assay, which was increased to 57% with the addition of theophylline. Dibutyryl cGMP showed only a mild (5%) stimulatory effect on mitotic activity. Dibutyryl cAMP enhanced keratinization in the epithelial cell outgrowths with the biogenesis of keratohyalin granules, whereas dibutyryl cGMP did not produce any observable alterations.     

Effect of inosine 5' -(beta, gamma-imido) triphosphate and other nucleotides on beef heart mitochondrial ATPase.

The effects of various substrates and alternative substrates on the hydrolytic activity of beef heart mitochondrial ATPase was examined. It was found that ATP or ADP, ITP hydrolysis showed positive cooperativity. IDP inhibited ITP hydrolysis and caused positive cooperativity. When ITP was present during an ATP hydrolysis assay, the rate of ATP hydrolysis was stimulated. IDP had no effect on ATP hydrolysis rates. A nonhydrolyzable ITP analog, inosine 5'-(beta, gamma-imido)triphosphate (IMP-P(NH)P), was synthesized and purified. It was found to be a potent competitive inhibitor of ITP and GTP hydrolytic activity. However, this beta-gamma-imido-bridged ITP analog was found to change the ITP and GTP hydrolysis kinetics from linear to positively cooperative. This compound inhibited ATP hydrolysis at substrate concentrations of 100 muM and lower, and stimulated ATP hydrolysis at substrate concentrations between 100 muM and 2 mM. IMP-P(NH)P had no effect on ATP hydrolysis when the substrate concentration was above 2 mM. In the presence of the activating anion, bicarbonate, IMP-P(NH)P inhibited ATP hydrolysis competitively, and induced positive cooperativity. IMP-P(NH)P had no effect on the ATP equilibrium Pi exchange, the ITP equilibrium Pi exchange, or ATP synthesis catalyzed by beef heart submitochondrial particles.     

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C1 repressor of phage P1 is inactivated by noncovalent binding of P1 Coi protein.

The temperate phage P1 encodes two genes whose products antagonize the action of the phage's C1 repressor of lytic functions, namely a distantly linked antirepressor gene, ant, and a closely linked c1 inactivator gene, coi. Starting with an inducible coi-recombinant plasmid, Coi protein was overproduced and purified to near homogeneity. By using a DNA mobility shift assay we demonstrate that Coi protein inhibits the operator binding of the C1 repressors of the closely related P1 and P7 phages. Coi protein (Mr = 7,600) exerts its C1-inactivating function by forming a complex with the C1 repressor (Mr = 32,500) at a molar ratio of about 1:1, as shown by density gradient centrifugation and gel filtration. C1 repressor and Coi protein are recovered in active form from the complex, suggesting that noncovalent interactions are the sole requirements for complex formation. The interplay of repressor and antagonists operating in the life cycle of P1 is discussed.     

8-Hydroxypegolettiolide,a sesquiterpene lactone with a new carbon skeleton and further constituents from Pegolettia senegalensis

The investigation of Pegolettia senegalensis afforded several new sesquiterpene lactones, eight cis-6,12-germacra-trans,trans-1(10),4,11-trienolides, five cis-6,12-eudesmanolides, two elemanolides, 8,14-cyclogermacra-1(10),4,7(11)-trien-6,12-olide with a new carbon skeleton, three germacra-1(10),4,11(13)-trien-12-oic acids with ester residues at C-8, 18-hydroxygeranyl nerol, 1,3-dihydroxyoctadecane and a mixture of esters of 3,4-dihydroxy-dihydrocinnamyl alcohol. The structures were elucidated by high field ¹HNMR spectroscopy and some chemical transformations. The C-10 configuration of 6,12-cis-eudesmanolides from Calostephane divaricata and Inula crithmoides most likely has to be corrected. The chemotaxonomic situation of the genus Pegolettia and biogenetic considerations are discussed briefly.     

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Antiphytovirale Aktivität von lipophilen Fraktionen aus der Hefe Lodderomyces elongisporus IMET H 128

Lipid extract isolated from biomasses of Lodderomyces elongisporus IMET H 128 grown on gas oil 7(B.p. 240–380°C) and fractions of the lipid extract (acetone soluble and fatty acid fractions) reduced the concentration of potato virus X in inoculated as well as in secondarily infected leaves markedly. The antiphytoviral inactive phosphatide fraction was converted into a fraction with high activity by partial hydrolysis with SO₂ as acting agent.