Deoxyadenosine/deoxycytidine kinase from Bacillus subtilis. Purification, characterization, and physiological function

Three different deoxyribonucleoside kinases with specificities toward thymidine, deoxyguanosine, and deoxyadenosine/deoxycytidine, respectively, are identified in Bacillus subtilis. The deoxyadenosin/deoxycytidine kinase is purified 950-fold employing blue Sepharose CL-6B column chromatography. The two deoxyribonucleoside kinase activities copurify and are present in the same band after polyacrylamide gel electrophoresis. The molecular weight is determined by gel filtration to be 47,000. Cytidine, adenosine, arabinosylcytosine, and arabinosyladenine are substrates for the enzyme. The activities toward these substrates are less than 20% of the activities obtained with deoxyadenosin and deoxycytidine. The deoxycytidine and deoxyadenosine saturation curves are hyperbolic with Km values for both nucleosides around 5 microM. The maximal velocities for the two deoxyribonucleosides are nearly identical with GTP as phosphate donor. GTP is the best donor showing hyperbolic saturation curves and Km values around 150 microM depending on the deoxyribonucleoside concentration. dATP and dCTP are inhibitors when GTP is the phosphate donor. They may both act as phosphate donors themselves. A divalent metal ion is required, Mg2+ giving the highest activity. A spontaneous mutant, selected as resistant to 5-fluorodeoxycytidine, lacks both deoxycytidine and deoxyadenosine kinase activity, while it retains normal activities toward deoxyguanosine, deoxyuridine, and thymidine.     

Molecular mechanisms of ceramide-mediated CD95 clustering.

Receptor clustering has been suggested as a crucial mechanism to initiate receptor signaling. Here we show that ceramide in sphingolipid-rich membrane rafts mediates clustering of CD95. Neutralization of surface ceramide or inhibition of its endogenous generation prevented CD95 clustering. Furthermore, application of ceramide at the cell surface triggered clustering of active but not inactive CD95. Apoptosis was inhibited by neutralization of surface ceramide or inhibition of ceramide release in vitro and in vivo. Thus, we conclude that surface ceramide mediates CD95 clustering, which is required for initiation of apoptosis, at least in some cell types.     

Biorefining of wood: combined production of ethanol and xylanase from waste fiber sludge

The possibility to utilize fiber sludge, waste fibers from pulp mills and lignocellulose-based biorefineries, for combined production of liquid biofuel and biocatalysts was investigated. Without pretreatment, fiber sludge was hydrolyzed enzymatically to monosaccharides, mainly glucose and xylose. In the first of two sequential fermentation steps, the fiber sludge hydrolysate was fermented to cellulosic ethanol with the yeast Saccharomyces cerevisiae. Although the final ethanol yields were similar, the ethanol productivity after 9.5?h was 3.3?g/l/h for the fiber sludge hydrolysate compared with only 2.2?g/l/h for a reference fermentation with similar sugar content. In the second fermentation step, the spent fiber sludge hydrolysate (the stillage obtained after distillation) was used as growth medium for recombinant Aspergillus niger expressing the xylanase-encoding Trichoderma reesei (Hypocrea jecorina) xyn2 gene. The xylanase activity obtained with the spent fiber sludge hydrolysate (8,500?nkat/ml) was higher than that obtained in a standard medium with similar monosaccharide content (1,400?nkat/ml). Analyses based on deglycosylation with N-glycosidase?F suggest that the main part of the recombinant xylanase was unglycosylated and had molecular mass of 20.7?kDa, while a minor part had N-linked glycosylation and molecular mass of 23.6?kDa. Chemical analyses of the growth medium showed that important carbon sources in the spent fiber sludge hydrolysate included xylose, small aliphatic acids, and oligosaccharides. The results show the potential of converting waste fiber sludge to liquid biofuel and enzymes as coproducts in lignocellulose-based biorefineries.     

CGS8216 noncompetitively antagonizes the discriminative effects of diazepam in rats

The benzodiazepine antagonist properties of CGS8216 were evaluated in rats trained to discriminate between saline and 1.0 mg/kg of diazepam in a two-choice, stimulus-shock termination procedure. CGS8216 (0.3 to 100 mg/kg) administered alone, either s.c., p.o. or i.p., occasioned only saline-appropriate responding. When administered concomitantly with a constant 1.0 mg/kg dose of diazepam, CGS8216 produced dose-related decreases in drug-appropriate responding. CGS8216 was most potent by the i.p. route, and approximately tenfold less potent by the oral route. CGS8216 was dermatotoxic after s.c. administration. CGS8216 i.p. had a long duration of action. A dose of 30 mg/kg completely antagonized the discriminative effects of the 1.0 mg/kg training dose of diazepam when the antagonist was administered 8 hr before the start of the test session. In order to determine the type of antagonism by CGS8216, the dose-effect curve for diazepam was redetermined in the presence of varying doses of CGS8216 (0.3 to 3.0 mg/kg, i.p.). CGS8216 produced a dose-related rightward shift in the diazepam dose-effect curve, but also decreased the slope and appeared to decrease the maximal effect. These results are consistent with the interpretation that CGS8216 antagonizes diazepam in a noncompetitive manner. It may do so because either it interacts with a subpopulation of benzodiazepine receptors, it functions as a pseudo-irreversible antagonist due to its high affinity, or because it is an antagonist with agonist properties.     

Adenosine mediates transforming growth factor-beta 1 release in kidney glomeruli of diabetic rats

Up regulation of the transforming growth factor-beta 1 (TGF-β1) axis has been recognized as a pathogenic event for progression of glomerulosclerosis in diabetic nephropathy. We demonstrate that glomeruli isolated from diabetic rats accumulate up to sixfold more extracellular adenosine than normal rats. Both decreased nucleoside uptake activity by the equilibrative nucleoside transporter 1 and increased AMP hydrolysis contribute to raise extracellular adenosine. Ex vivo assays indicate that activation of the low affinity adenosine A_2B receptor subtype (A_2BAR) mediates TGF-β1 release from glomeruli of diabetic rats, a pathogenic event that could support progression of glomerulopathy when the bioavailability of adenosine is increased.