A kilonova as the electromagnetic counterpart to a gravitational-wave source.

Gravitational waves were discovered with the detection of binary black-hole mergers and they should also be detectable from lower-mass neutron-star mergers. These are predicted to eject material rich in heavy radioactive isotopes that can power an electromagnetic signal. This signal is luminous at optical and infrared wavelengths and is called a kilonova. The gravitational-wave source GW170817 arose from a binary neutron-star merger in the nearby Universe with a relatively well confined sky position and distance estimate. Here we report observations and physical modelling of a rapidly fading electromagnetic transient in the galaxy NGC 4993, which is spatially coincident with GW170817 and with a weak, short γ-ray burst. The transient has physical parameters that broadly match the theoretical predictions of blue kilonovae from neutron-star mergers. The emitted electromagnetic radiation can be explained with an ejected mass of 0.04 ± 0.01 solar masses, with an opacity of less than 0.5 square centimetres per gram, at a velocity of 0.2 ± 0.1 times light speed. The power source is constrained to have a power-law slope of -1.2 ± 0.3, consistent with radioactive powering from r-process nuclides. (The r-process is a series of neutron capture reactions that synthesise many of the elements heavier than iron.) We identify line features in the spectra that are consistent with light r-process elements (atomic masses of 90-140). As it fades, the transient rapidly becomes red, and a higher-opacity, lanthanide-rich ejecta component may contribute to the emission. This indicates that neutron-star mergers produce gravitational waves and radioactively powered kilonovae, and are a nucleosynthetic source of the r-process elements.

Crystallization and preliminary X-ray diffraction analysis of a type I beta-glucosidase encoded by the bgIA gene of Bacillus polymyxa.

The enzyme encoded by the bgIA gene of Bacillus polymyxa, a type I beta-glucosidase belonging to family I of glycosyl hydrolases, has been purified to homogeneity from an Escherichia coli culture which overexpressed the gene, and crystallized. The crystals, which diffract to 3.0 A resolution, belong to the orthorhombic space group C222(1). The cell dimensions are a = 155.4 A, b = 209.4 A, c = 209.7 A.

[Use of intraoperative lymphoscintigraphy in doubtful cases of sentinel node detection]. / Uso de la linfogammagrafía intraoperatoria en los casos dudosos de detección del ganglio centinela.

Lymphoscintigraphy is a widely accepted method used to detect selectively the sentinel node in malignant melanoma. This is the case report of a patient who was operated on for an inguinal melanoma and who was referred to the Nuclear Medicine Section for preoperative lymphoscintigraphy. There were technical problems for sentinel node detection due to the proximity of injection points. We aimed to know the possibility to perform an intraoperative lymphoscintigraphy as a valid and useful technique in cases as this one.

Purification and characterization of a Bacillus polymyxa beta-glucosidase expressed in Escherichia coli.

The beta-glucosidase encoded by the bglA gene from Bacillus polymyxa was overproduced in Escherichia coli by using a plasmid in which bglA is under control of the lacI promoter. Induction with isopropyl-beta-D-thiogalactopyranoside allowed an increase in the specific activity of the enzyme of about 100 times the basal level of gene expression. The enzyme was purified by a two-step procedure involving salting out with ammonium sulfate and ion-exchange chromatography with DEAE-cellulose. Fractions of beta-glucosidase activity recovered by this procedure, after electrophoresis in an acrylamide gel and staining with silver nitrate, yielded a single band of protein. This band was shown by a zymogram to correspond to beta-glucosidase activity. The purified protein showed an apparent molecular mass of 50 kDa and an isoelectric point of 4.6, values in agreement with those expected from the nucleotide sequence of the gene. Km values of the enzyme, with either cellobiose or p-nitrophenyl-beta-D-glucoside as the substrate, were determined. It was shown that the enzyme is competitively inhibited by glucose. The effects of different metallic ions and other agents were studied. Hg2+ was strongly inhibitory, while none of the other cations tested had any significant effect. Ethanol did not show the stimulating effect observed with other beta-glucosidases. The mechanism of enzyme action was investigated. High-pressure liquid chromatography analysis with cellobiose as the substrate confirmed previous data revealing the formation of two products, glucose and another, unidentified, compound. Results presented here indicate that this compound is cellotriose formed by transglycosylation.

Cloning and characterization of two genes from Bacillus polymyxa expressing beta-glucosidase activity in Escherichia coli.

DNA fragments from Bacillus polymyxa which encode beta-glucosidase activity were cloned in Escherichia coli by selection of yellow transformants able to hydrolyze the artificial chromogenic substrate p-nitrophenyl-beta-D-glucopyranoside. Restriction endonuclease maps and Southern analysis of the cloned fragments showed the existence of two different genes. Expression of either one of these genes allowed growth of E. coli in minimal medium with cellobiose as the only carbon source. One of the two enzymes was found in the periplasm of E. coli, hydrolyzed arylglucosides more actively than cellobiose, and rendered glucose as the only product upon cellobiose hydrolysis. The other enzyme was located in the cytoplasm, was more active toward cellobiose, and hydrolyzed this disaccharide, yielding glucose and another, unidentified compound, probably a phosphorylated sugar.

Purification and Characterization of Alkaline Xylanases from Bacillus polymyxa.

By applying different classical and fast protein liquid chromatographic techniques, three xylanases (beta-1,4-d-xylan xylanhydrolase) were purified to homogeneity from the extracellular enzymatic complex of Bacillus polymyxa. The three enzymes (X(34)C, X(34)E, and X(22)) were small proteins of 34, 34, and 22 kDa and basic pIs 9.3, >9.3, and 9.0, respectively. X(34)C and X(34)E are closely related and seem to be isoforms of the same enzyme. However, they differ in some characteristics. The three enzymes had different pH and temperature optima. One of them, X(34)E, showed a high thermal stability. The V(max) values determined for X(34)C, X(34)E, and X(22) enzymes on oat spelts xylan were 14.9, 85.5, and 64.0 U mg, respectively, and 16.1, 62.0, and 150.6 U mg on birchwood xylan. When oat spelts xylan was the substrate used, K(m) values of 3.4, 2.4, and 1.9 mg ml were obtained for X(34)C, X(34)E, and X(22) enzymes, respectively, and 0.65, 6.3, and 0.32 mg ml were the respective K(m) values determined with birchwood xylan as the substrate. The enzymes were nondebranching endo-beta-xylanases. Xylose was one of the products of xylan hydrolysis by xylanases X(34)C and X(34)E, but this monosaccharide was not released by X(22) enzyme. However, neither of the enzymes was able to degrade xylobiose.

Uso de la linfogammagrafía intraoperatoria en los casos dudosos de detección del ganglio centinela / Use of intraoperative lymphoscintigraphy in doubtful cases of sentinel node detection

La linfogammagrafía es una técnica ampliamente aceptada para la detección selectiva del ganglio centinela en el melanoma maligno. Presentamos el caso de un paciente intervenido de un melanoma inguinal y que fue remitido al Servicio de Medicina Nuclear para una linfogammagrafía preoperatoria. Existieron problemas técnicos para la detección del ganglio centinela debido a su cercanía con los puntos de inyección. Nosotros planteamos como objetivo la posibilidad de realizar una linfogammagrafía intraoperatoria como técnica válida y de ayuda en casos como el que describimos

Lymphoscintigraphy is a widely accepted method used to detect selectively the sentinel node in malignant melanoma. This is the case report of a patient who was operated on for an inguinal melanoma and who was referred to the Nuclear Medicine Section for preoperative lymphoscintigraphy. There were technical problems for sentinel node detection due to the proximity of injection points. We aimed to know the possibility to perform an intraoperative lymphoscintigraphy as a valid and useful technique in cases as this one