Large excess of heavy nitrogen in both hydrogen cyanide and cyanogen from comet 17P/Holmes

From millimeter and optical observations of the Jupiter-family comet 17P/Holmes performed soon after its huge outburst of October 24, 2007, we derive 14 N/15N = 139 +/- 26 in HCN, and 14N/15N = 165 +/- 40 in CN, establishing that HCN has the same non-terrestrial isotopic composition as CN. The same conclusion is obtained for the long-period comet C/1995 O1 (Hale-Bopp) after a reanalysis of previously published measurements. These results are compatible with HCN being the prime parent of CN in cometary atmospheres. The 15N excess relative to the Earth atmospheric value indicates that N-bearing volatiles in the solar nebula underwent important N isotopic fractionation at some stage of Solar System formation. HCN molecules never isotopically equilibrated with the main nitrogen reservoir in the solar nebula before being incorporated in Oort-cloud and Kuiper-belt comets. The 12C/13C ratios in HCN and CN are measured to be consistent with the terrestrial value.Comment: Accepted for publication in the Astrophysical Journal (Letters) 4 page

Deep Impact : High Resolution Optical Spectroscopy with the ESO VLT and the Keck 1 telescope

We report on observations of comet 9P/Tempel 1 carried out before, during, and after the NASA DEEP IMPACT event (UT July 4), with the optical spectrometers UVES and HIRES mounted on the telescopes Kueyen of the ESO VLT (Chile) and Keck 1 on Mauna Kea (Hawaii), respectively. A total observing time of about 60 hours, distributed over 15 nights around the impact date, allowed us (i) to find a periodic variation of 1.709 +/- 0.009 day in the CN and NH flux, explained by the presence of two major active regions; (ii) to derive a lifetime > ~ 5 x 10^4 s for the parent of the CN radical from a simple modeling of the CN light curve after the impact; (iii) to follow the gas and dust spatial profiles evolution during the 4 hours following the impact and derive the projected velocities (400 m/s and 150 m/s respectively); (iv) to show that the material released by the impact has the same carbon and nitrogen isotopic composition as the surface material (12C/13C = 95 +/- 15 and 14N/15N = 145 +/- 20).Comment: Accepted for publication in ApJ Letter

The impact and rotational lightcurves of Comet 9P/Tempel 1

UVES and HIRES high-resolution spectra of comet 9P/Tempel 1 are used to investigate the impact and rotational light curves of various species with a view toward building a simple model of the distribution and activity of the sources. The emission by OH, NH, CN, C3, CH, C2, NH2 and OI, are analyzed, as well as the light scattered by the dust. It is found that a simple model reproduces fairly well the impact lightcurves of all species combining the production of the observed molecules and the expansion of the material throughout the slit. The rotational light curve for each species is explained in terms of a single model with three sources.Comment: 34 pages, 11 figures Accepted for publication in the special issue of Icarus associated with the Deep Impact mission to Comet 9P/Tempel

Stellar Archaeology: a Keck Pilot Program on Extremely Metal-Poor Stars from the Hamburg/ESO Survey. II. Abundance Analysis

We present a detailed abundance analysis of 8 stars selected as extremely metal poor candidates from the Hamburg/ESO Survey (HES). For comparison, we have also analysed 3 extremely metal-poor candidates from the HK survey, and 3 additional bright metal-poor stars. With this work, we have doubled the number of extremely metal-poor stars ([Fe/H]$\le 3.0$) with high-precision abundance analyses. Our sample of extremely metal-poor candidates from the HES contains 3 stars with [Fe/H] $\le -3.0$, 3 more with [Fe/H]$\le -2.8$, and 2 stars that are only slightly more metal rich. Thus, the chain of procedures that led to the selection of these stars from the HES successfully provides a high fraction of extremely metal-poor stars. We verify that our stellar parameters, derived in Paper I, lead to acceptable ionization and excitation balances for Fe, ruling out substantial non-LTE effects in Fe. For the $\alpha-$elements Mg, Si, Ca, Ti, the light element Al, the iron-peak elements Sc, Cr, Mn, and the neutron capture elements Sr and Ba, we find trends in abundance ratios [X/Fe] similar to those found by previous studies. However,the scatter in most of these ratios, even at [Fe/H]$\le -3.0$ dex, is surprisingly small. Only Sr and Ba show scatter larger than the expected errors. Future work (the 0Z project) will provide much stronger constraints on the scatter (or lack thereof) in abundances for a greater number of stars. We discuss the implications of these results for the early chemical evolution of the Galaxy, including such issues as the number of contributing SN, and the sizes of typical fragments in which they were born. In addition, we have identified a very metal poor star that appears to be the result of the s-process chain, operating in a very metal-poor environment, with extremely enhanced C, Ba, and Pb, and somewhat enhanced Sr.Comment: 36 pages, 9 tables, 14 figures included; accepted for publication in the July 2002 issue of The Astronomical Journa

Isolation and Characterization of EstC, a New Cold-Active Esterase from Streptomyces coelicolor A3(2)

The genome sequence of Streptomyces coelicolor A3(2) contains more than 50 genes coding for putative lipolytic enzymes. Many studies have shown the capacity of this actinomycete to store important reserves of intracellular triacylglycerols in nutrient depletion situations. In the present study, we used genome mining of S. coelicolor to identify genes coding for putative, non-secreted esterases/lipases. Two genes were cloned and successfully overexpressed in E. coli as His-tagged fusion proteins. One of the recombinant enzymes, EstC, showed interesting cold-active esterase activity with a strong potential for the production of valuable esters. The purified enzyme displayed optimal activity at 35°C and was cold-active with retention of 25% relative activity at 10°C. Its optimal pH was 8.5–9 but the enzyme kept more than 75% of its maximal activity between pH 7.5 and 10. EstC also showed remarkable tolerance over a wide range of pH values, retaining almost full residual activity between pH 6–11. The enzyme was active toward short-chain p-nitrophenyl esters (C2–C12), displaying optimal activity with the valerate (C5) ester (kcat/Km = 737±77 s−1 mM−1). The enzyme was also very active toward short chain triglycerides such as triacetin (C2:0) and tributyrin (C4:0), in addition to showing good primary alcohol and organic solvent tolerance, suggesting it could function as an interesting candidate for organic synthesis of short-chain esters such as flavors

Carboxylic ester hydrolases from hyperthermophiles

Carboxylic ester hydrolyzing enzymes constitute a large group of enzymes that are able to catalyze the hydrolysis, synthesis or transesterification of an ester bond. They can be found in all three domains of life, including the group of hyperthermophilic bacteria and archaea. Esterases from the latter group often exhibit a high intrinsic stability, which makes them of interest them for various biotechnological applications. In this review, we aim to give an overview of all characterized carboxylic ester hydrolases from hyperthermophilic microorganisms and provide details on their substrate specificity, kinetics, optimal catalytic conditions, and stability. Approaches for the discovery of new carboxylic ester hydrolases are described. Special attention is given to the currently characterized hyperthermophilic enzymes with respect to their biochemical properties, 3D structure, and classification

Environmental factors modulating the stability and enzymatic activity of the Petrotoga mobilis Esterase (PmEst)

Enzymes isolated from thermophilic organisms found in oil reservoirs can find applications in many fields, including the oleochemical, pharmaceutical, bioenergy, and food/dairy industries. In this study, in silico identification and recombinant production of an esterase from the extremophile bacteria Petrotoga mobilis (designated PmEst) were performed. Then biochemical, bioinformatics and structural characterizations were undertaken using a combination of synchrotron radiation circular dichroism (SRCD) and fluorescence spectroscopies to correlate PmEst stability and hydrolytic activity on different substrates. The enzyme presented a high Michaelis-Menten constant (KM 0.16 mM) and optimum activity at ~55°C for p-nitrophenyl butyrate. The secondary structure of PmEst was preserved at acid pH, but not under alkaline conditions. PmEst was unfolded at high concentrations of urea or guanidine through apparently different mechanisms. The esterase activity of PmEst was preserved in the presence of ethanol or propanol and its melting temperature increased ~8°C in the presence of these organic solvents. PmEst is a mesophilic esterase with substrate preference towards short-to medium-length acyl chains. The SRCD data of PmEst is in agreement with the prediction of an α/β protein, which leads us to assume that it displays a typical fold of esterases from this family. The increased enzyme stability in organic solvents may enable novel applications for its use in synthetic biology. Taken together, our results demonstrate features of the PmEst enzyme that indicate it may be suitable for applications in industrial processes, particularly, when the use of polar organic solvents is required

Characterization of an extracellular lipase and its chaperone from Ralstonia eutropha H16

Lipase enzymes catalyze the reversible hydrolysis of triacylglycerol to fatty acids and glycerol at the lipid–water interface. The metabolically versatile Ralstonia eutropha strain H16 is capable of utilizing various molecules containing long carbon chains such as plant oil, organic acids, or Tween as its sole carbon source for growth. Global gene expression analysis revealed an upregulation of two putative lipase genes during growth on trioleate. Through analysis of growth and activity using strains with gene deletions and complementations, the extracellular lipase (encoded by the lipA gene, locus tag H16_A1322) and lipase-specific chaperone (encoded by the lipB gene, locus tag H16_A1323) produced by R. eutropha H16 was identified. Increase in gene dosage of lipA not only resulted in an increase of the extracellular lipase activity, but also reduced the lag phase during growth on palm oil. LipA is a non-specific lipase that can completely hydrolyze triacylglycerol into its corresponding free fatty acids and glycerol. Although LipA is active over a temperature range from 10 °C to 70 °C, it exhibited optimal activity at 50 °C. While R. eutropha H16 prefers a growth pH of 6.8, its extracellular lipase LipA is most active between pH 7 and 8. Cofactors are not required for lipase activity; however, EDTA and EGTA inhibited LipA activity by 83 %. Metal ions Mg[superscript 2+], Ca[superscript 2+], and Mn[superscript 2+] were found to stimulate LipA activity and relieve chelator inhibition. Certain detergents are found to improve solubility of the lipid substrate or increase lipase-lipid aggregation, as a result SDS and Triton X-100 were able to increase lipase activity by 20 % to 500 %. R. eutropha extracellular LipA activity can be hyper-increased, making the overexpression strain a potential candidate for commercial lipase production or in fermentations using plant oils as the sole carbon source.Malaysia-MIT Biotechnology Partnership Programm