Cyclic-AMP binding to the cell surface during development of Dictyostelium discoideum

Abstract. Cell aggregation in Dictyostelium discoideum is a chemotactic process mediated by cyclic adenosine monophosphate (CAMP), which is detected by cell surface receptors. The cAMP signal is degraded by cAMP phosphodiesterase. The possibility that cAMP signals are also used for cell communication in the multicellular stages was studied by determining whether the cAMP receptors, which are essential for signal transduction, continue to function in these stages. During slug migration, the number of binding sites per cell decreases to about 15% of the maximum level acquired during aggregation. At the onset of fruiting body formation, a three- to Four-Fold increase in cAMP binding activity occurs. This increase coincides with an increase in cAMP phosphodiesterase. Both phenomena suggest that cell-cell communication mediated by cAMP is used during culmination. During both slug migration and early culmination, the prestalk cells exhibit about twice as much binding activity as the prespore cells.     

Functional analysis of the Agrobacterium tumefaciens octopine Ti-plasmid left and right T-region border fragments

Summary Border fragments of the octopine Ti-plasmid were tested for their ability to restore tumorigenicity of an avirulent mutant carrying a deleted right border. It was found that neither introduction of left border fragments nor that of small right border fragments at the position of the deletion resulted in a complete restoration of oncogenicity. However, insertion of a larger right border fragment in the deletion mutant gave fully oncogenic strains. In the latter case sequences to the right side of the right border repeat were found to be responsible for a complete restoration of oncogenicity. Also a left border repeat inserted together with this enhancer sequence fully restored the oncogenicity of the deletion mutant. The enhancer-sequence on itself was not able to mediate the transfer of the T-region to the plant cell. Border fragments inserted in inverted orientation in the deletion mutant were able to mediate the transfer of the T-region to the plant cell, but at a reduced frequency.     

The histone H1°/H5 variant and terminal differentiation of cells during development of Xenopus laevis

The maintenance of the differentiated condition is supposed to be associated with the presence of a histone of the H1(0)/H5 subclass. If the H1(0)/H5 variant has an important role in differentiation distinct from that of H1, it should display differential expression in time and position during development. Here we report that this prediction is verified during Xenopus laevis development, in which tadpoles exhibit a very characteristic, developmentally regulated pattern of histone H1(0)/H5 expression that is different for the derivatives of each embryonic germ layer. However, the pattern of appearance of this variant during development does not reflect a simple correlation between its presence and the state of differentiation. Therefore, these results are pertinent to current ideas on differentiation and the involvement of lysine-rich histones in the repression of eukaryotic genes.     

Complement C4 phenotypes in dementia of the Alzheimer type

Complement C4 phenotype distribution was studied in 64 patients with dementia of the Alzheimer type. In contrast to reported findings we failed to find a significant association between C4B2 gene frequency and Alzheimer's dementia.     

The hydrolysis of triglycerides by immobilized lipase in a hydrophilic membrane reactor

In the present article a method is described to immobilize lipase from Candida rugosa on a hollow fiber membrane, and the use of such a system for the hydrolysis of lipids is reported. The membranes were ENKA hydro philic Cuprophan((R))-type hollow fibers, having a large specific surface area. The immobilized lipase exhibited a high stability: the half-life time was 43 days at a temperature of 30 degrees C. Furthermore, it is proved that kinetic studies can be carried out with this system, operated in a batch or continuous mode. The relation between conversion rate and degree of hydrolysis was determined. On this basis, a dynamic model of the process was developed that describes the relation between reaction conditions and the conversion rate.     

Yeast species utilizing uric acid,adenine,n-alkylamines or diamines as sole source of carbon and energy

Yeast strains utilizing uric acid, adenine, monoamines or diamines as sole source of carbon and energy were isolated from several soil samples by the enrichment culture method. The most common species wasTrichosporon cutaneum. Strains ofCandida catenulata, C. famata, C. parapsilosis, C. rugosa, Cryptococcus laurentii, Stephanoascus ciferrii andTr. adeninovorans were also isolated. All strains utilizing uric acid as sole carbon source utilized some primaryn-alkyl-l-amines hydroxyamines or diamines as well. The ascomycetous yeast strains showing these characteristics all belonged to species known to assimilate hydrocarbons. Type strains of hydrocarbon-positive yeast species which were not found in the enrichment cultures generally assimilated putrescine, some type strains also butylamine or pentylamine, but none assimilated uric acid. Methanol-positive species were not isolated. Type strains of methanol-positive and of hydrocarbon-negative species did not assimilate uric acid, butylamine or putrescine. Assimilation of putrescine as sole source of carbon and energy may be a valuable diagnostic criterion in yeast taxonomy.     

Degradation of some phenols and hydroxybenzoates by the imperfect ascomycetous yeastsCandida parapsilosis andArxula adeninivorans: evidence for an operative gentisate pathway

The imperfect ascomycetous yeastsCandida parapsilosis andArxula adeninivorans degraded 3-hydroxybenzoic acid via gentisate which was the cleavage substrate. 4-Hydroxybenzoic acid was metabolized via protocatechuate. No cleavage enzyme for the latter was detected. In stead of this NADH- and NADPH-dependent monooxygenases were present. In cells grown at the expense of hydroquinone and 4-hydroxygenzoic acid, enzymes of the hydroxyhydroquinone variant of the 3-oxoadipate pathway were demonstrated, which also took part in the degradation of 2,4-dihydroxybenzoic acid byC. parapsilosis.Abbreviations HHQ Hydroxyhydroquinone (1,2,4-trihydroxybenzene) - GSH reduced Glutathione     

Instar-specific mortalities of coexisting Daphnia species in relation to food and invertebrate predation

Instar-specific mortalities of Daphnia hyalina and D.cucullatawere studied from May 19 to September 29, 1988 in combinationwith invertebrate predator and phytoplankton abundance. Simultaneouslife-table experiments were conducted under semi-natural conditionsin the laboratory to estimate juvenile mortality in a predator-freeenvironment. Juvenile mortality by predation was calculatedas the difference between juvenile mortality in the field andin the experiments and was the most important factor for thedifferences in abundance of the two species. For D.hyalina juvenilemortality was higher in early summer and probably caused byselective predation by Chaoborus flavicans. Predation by Leptodorakindtii was probably more important during the rest of the summer.Estimated mortality by predation adequately explained juvenilemortality, except for a 3-week period in August. Decreasingflagellate densities in July were accompanied by increased juvenilemortalities of D.hyalina and D.cucullata in the life-table experimentsin August and coincided with a Daphnia population decrease.     

Kinetics of growth and sugar consumption in yeasts

An overview is presented of the steady- and transient state kinetics of growth and formation of metabolic byproducts in yeasts.Saccharomyces cerevisiae is strongly inclined to perform alcoholic fermentation. Even under fully aerobic conditions, ethanol is produced by this yeast when sugars are present in excess. This so-called Crabtree effect probably results from a multiplicity of factors, including the mode of sugar transport and the regulation of enzyme activities involved in respiration and alcoholic fermentation. The Crabtree effect inS. cerevisiae is not caused by an intrinsic inability to adjust its respiratory activity to high glycolytic fluxes. Under certain cultivation conditions, for example during growth in the presence of weak organic acids, very high respiration rates can be achieved by this yeast.S. cerevisiae is an exceptional yeast since, in contrast to most other species that are able to perform alcoholic fermentation, it can grow under strictly anaerobic conditions.Non-Saccharomyces yeasts require a growth-limiting supply of oxygen (i.e. oxygen-limited growth conditions) to trigger alcoholic fermentation. However, complete absence of oxygen results in cessation of growth and therefore, ultimately, of alcoholic fermentation. Since it is very difficult to reproducibly achieve the right oxygen dosage in large-scale fermentations, non-Saccharomyces yeasts are therefore not suitable for large-scale alcoholic fermentation of sugar-containing waste streams. In these yeasts, alcoholic fermentation is also dependent on the type of sugar. For example, the facultatively fermentative yeastCandida utilis does not ferment maltose, not even under oxygen-limited growth conditions, although this disaccharide supports rapid oxidative growth.