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  • 1
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    Lead isotope ratios for manganese nodules (2023)
    PANGAEA
    Details
    Publication Date: 2024-02-29
    Description: The authors have selected manganese nodules broadly representative of world oceanic areas. Approximately 1 gram of each manganese nodules was leached with 25-mi 6N HC1. Lead was extracted from the supernate by conventional anion exchange techniques, followed by a single dithizone extraction. Lead-isotope ratios were determined by mass spectrometry.
    Keywords: Albatross (1882-1921); Albatross1904-1905; ALBTR-4711; Atlantic Ocean; Carlsberg Ridge; CH05801; CH58-9RD; Chain; D16; D6269; Deposit type; DEPTH, sediment/rock; Discovery (1962); DOWNWIND-H; Dredge; Dredge, rock; DRG; DRG_R; DWHD47; Elevation of event; ELT24; ELT24.015-RS; ELT28; ELT28-5; Eltanin; ELT-BT14-3; Event label; Geochemistry; Horizon; Identification; Latitude of event; Lead; Lead-206/Lead-204 ratio; Lead-207/Lead-204 ratio; Lead-208/Lead-204 ratio; Longitude of event; manganese micronodule; manganese nodule; Mass spectrometry; NOAA and MMS Marine Minerals Geochemical Database; NOAA-MMS; ocean; Pacific Ocean; SAN_JUAN_1963; SCORPIO; sediment; SNJ-DH2; Southern Ocean; Spencer F. Baird; Sta 100; TRAWL; Trawl net; V20; V20-4RD; Vema
    Type: Dataset
    Format: text/tab-separated-values, 60 data points
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    DATA PANGAEA
  • 2
    Electronic Resource
    Electronic Resource
    Does squaring the quantum Monte Carlo weights give the exact quantum probability distribution? (1990)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 92 (1990), S. 2118-2120 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: It is shown that the recently-proposed method of East et al. [J. Chem. Phys. 89, 4880 (1988)] for stochastically obtaining the exact quantum mechanical probability distribution ||φ||2 is in error. The Green's function generator for the proposed process results in a Schrödinger-like equation for which ||φ||2 is not a solution. We carefully follow the logic of East et al. to discover their error.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.457998
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  • 3
    Electronic Resource
    Electronic Resource
    Effects of donor and acceptor peptides on concomitant hydrolysis and transfer reactions catalyzed by the exocellular DD-carboxypeptidase-transpeptidase from Streptomyces R39 (1974)
    s.l. : American Chemical Society
    Biochemistry 13 (1974), S. 2539-2547 
    Details
    ISSN: 1520-4995
    Source: ACS Legacy Archives
    Topics: Biology , Chemistry and Pharmacology
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1021/bi00709a010
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  • 4
    Electronic Resource
    Electronic Resource
    Valence quantum Monte Carlo with ab initio effective core potentials (1987)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 87 (1987), S. 1130-1136 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: Effective-core potentials (ECP's) obtained from ab initio methods are implemented in molecular quantum Monte Carlo (QMC). The theory is presented, and applied to the calculation of electron affinities (EA) of Li and Na, the ionization potential (IP) of Mg, the binding energies (De) of NaH and Na2, and the potential energy curve of Na2. In all cases ECP–QMC results are found to be as accurate as previous all-electron results. In particular, the calculated quantities (vs experimental values) are (in eV): EA(Li)=0.611±0.020 (0.620), EA(Na)=0.555±0.021 (0.546), IP(Mg)=7.637±0.026 (7.646), De (NaH) =1.954±0.073 (1.971), and De (Na2)=0.746±0.020 (0.747). In addition, the statistical precision obtained surpasses that which can be readily achieved in all-electron QMC calculations on these systems.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.453345
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  • 5
    Electronic Resource
    Electronic Resource
    Quantum Monte Carlo calculation of the singlet–triplet splitting in methylene (1985)
    College Park, Md. : American Institute of Physics (AIP)
    The Journal of Chemical Physics 82 (1985), S. 1983-1990 
    Details
    ISSN: 1089-7690
    Source: AIP Digital Archive
    Topics: Physics , Chemistry and Pharmacology
    Notes: The fixed-node quantum Monte Carlo (QMC) method is used to calculate the total energy of CH2 in the 3B1 and 1A1 states. For both states, the best QMC variationally bounded energies lie more than 15 kcal/mol (0.024 h) below the best previous variational calculations. Subtracting these energies to obtain the singlet–triplet splitting yields Te=9.4±2.2 kcal/mol. Adjusting for zero-point energies and relativistic effects, we obtain T0=8.9±2.2 kcal/mol. This result is in excellent agreement with the recent direct measurements of McKellar et al. of T0=9.05±0.06 kcal/mol, and of Leopold et al. of ∼9 kcal/mol, as well as with recent threoretical investigations which indicate an energy gap of 9–11 kcal/mol. We summarize the QMC method, discuss a possible scheme for iteratively correcting the procedure, and note that the present results were obtained using only single determinant functions for both states, in contrast to conventional ab initio approaches which must use at least two configurations to properly describe the singlet state.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.448381
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  • 6
    Electronic Resource
    Electronic Resource
    Quantitative analysis of the metabolism of soluble cytoplasmic peptidoglycan precursors of glycopeptide-resistant enterococci (1996)
    Oxford BSL : Blackwell Science Ltd
    Molecular microbiology 21 (1996), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Transposon Tn1546 from Enterococcus faecium BM4147 mediates high-level resistance to the glycopeptide antibiotics vancomycin and teicoplanin. Tn1546 encodes a dehydrogenase (VanH) and a ligase (VanA) that synthesize D-alanyl-D-lactate (D-Ala-D-Lac), a DD-dipeptidase (VanX) that hydrolyses D-Ala-D-Ala and a two-component regulatory system (VanR–VanS) that controls transcription of the vanHAX operon. Strains of Enterococcus faecalis harbouring various copy numbers of the vanRSHAX cluster were tested to determine if there was a correlation between the levels of resistance to glycopeptides, the levels of expression of the corresponding resistance genes and the relative proportions of the different cytoplasmic peptidoglycan precursors. Increased transcription of the vanHAX operon was associated with increased incorporation of D-Ala-D-Lac into peptidoglycan precursors to the detriment of D-Ala-D-Ala, and with a gradual increase in the vancomycin-resistance levels. More complete elimination of D-Ala-D-Ala-containing precursors was required for teicoplanin resistance. The VanY and VanZ proteins also encoded by Tn1546 were not effectors of the regulation of the vanHAX operon but contributed to vancomycin and teicoplanin resistance, respectively. Differences at the regulatory level accounted for phenotypic diversity in acquired glycopeptide resistance by production of D-lac-ending precursors.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2958.1996.00617.x
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  • 7
    Electronic Resource
    Electronic Resource
    Mutations leading to increased levels of resistance to glycopeptide antibiotics in VanB-type enterococci (1997)
    Oxford, UK : Blackwell Science Ltd
    Molecular microbiology 25 (1997), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: The vanB gene cluster mediates glycopeptide resistance by production of peptidoglycan precursors ending in the depsipeptide D-alanyl-D-lactate (D-Ala-D-Lac) instead of D-Ala-D-Ala found in susceptible enterococci. Synthesis of D-Ala-D-Lac and hydrolysis of D-Ala-D-Ala is controlled by the VanRBSB two-component regulatory system that activates transcription of the resistance genes in response to vancomycin but not to teicoplanin. Two substitutions (A30→G or D168→Y) in the VanSB sensor kinase resulted in induction by teicoplanin, indicating that the N-terminal domain of the protein was involved in glycopeptide sensing. A substitution (T237→K) located in the vicinity of the putative autophosphorylation site of VanSB (H233) was associated with a constitutive phenotype and affected a conserved residue known to be critical for the phosphatase activity of related kinases. A mutant producing an impaired host D-Ala:D-Ala ligase required vancomycin for growth, since D-Ala-D-Lac was only produced under inducing conditions. The ddl and vanSB mutations, alone or in combination, resulted in various resistance phenotypes that were determined by the amount of D-Ala-D-Ala and D-Ala-D-Lac incorporated into peptidoglycan precursors under different inducing conditions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2958.1997.4401812.x
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  • 8
    Electronic Resource
    Electronic Resource
    Glycopeptide resistance mediated by enterococcal transposon Tn 1546 requires production of VanX for hydrolysis of D-alanyl-D-alanine (1994)
    Oxford, UK : Blackwell Publishing Ltd
    Molecular microbiology 13 (1994), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Cloning and nucleotide sequencing indicated that transposon Tn 1546 from Enterococcus faecium BM4147 encodes a 23365 Da protein, VanX, required for glycopeptide resistance. The vanX gene was located downstream from genes encoding the VanA ligase and the VanH dehydrogenase which synthesize the depsipeptide D-alanyl-D-lactate (D-Ala-D-Lac). In the presence of ramoplanin, an Enterococcus faecalis JH2-2 derivative producing VanH, VanA and VanX accumulated mainly UDP-MurNAc-L-Ala-γ-D-Glu-L-Lys-D-Ala-D-Lac (pentadepsipeptide) and small amounts of UDP-MurNAc-L-Ala-γ-D-Glu-L-Lys-D-Ala-D-Ala (pentapeptide) in the ratio 49:1. Insertional inactivation of vanX led to increased synthesis of pentapeptide with a resulting change in the ratio of pentadepsipeptide: pentapeptide to less than 1:1. Expression of vanX in E. faecalis and Escherichia coli resulted in production of a D,D-dipeptidase that hydrolysed D-Ala-D-Ala. Pentadepsipeptide, pentapeptide and D-Ala-D-Lac were not substrates for the enzyme. These results establish that VanX is required for production of a D,D-dipeptidase that hydrolyses D-Ala-D-Ala, thereby preventing pentapeptide synthesis and subsequent binding of glycopeptides to D-Ala-D-Ala-containing peptidoglycan precursors at the cell surface.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1111/j.1365-2958.1994.tb00497.x
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  • 9
    Electronic Resource
    Electronic Resource
    Gene vanXYC encodes d,d -dipeptidase (VanX) and d,d-carboxypeptidase (VanY) activities in vancomycin-resistant Enterococcus gallinarum BM4174 (1999)
    Oxford BSL : Blackwell Science Ltd
    Molecular microbiology 34 (1999), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: VanX and VanY have strict d,d-dipeptidase and d,d-carboxypeptidase activity, respectively, that eliminates production of peptidoglycan precursors ending in d-alanyl-d-alanine (d-Ala-d-Ala) in glycopeptide-resistant enterococci in which the C-terminal d-Ala residue has been replaced by d-lactate. Enterococcus gallinarum BM4174 synthesizes peptidoglycan precursors ending in d-Ala-d-serine (d-Ala-d-Ser) essential for VanC-type vancomycin resistance. Insertional inactivation of the vanC-1 gene encoding the ligase that catalyses synthesis of d-Ala-d-Ser has a polar effect on both d,d-dipeptidase and d,d-carboxypeptidase activities. The open reading frame downstream from vanC-1 encoded a soluble protein designated VanXYC (Mr 22 318), which had both of these activities. It had 39% identity and 74% similarity to VanY in an overlap of 158 amino acids, and contained consensus sequences for binding zinc, stabilizing the binding of substrate and catalysing hydrolysis that are present in both VanX- and VanY-type enzymes. It had very low dipeptidase activity against d-Ala-d-Ser, unlike VanX, and no activity against UDP-MurNAc-pentapeptide[d-Ser], unlike VanY. The introduction of plasmid pAT708(vanC-1,XYC) or pAT717(vanXYC) into vancomycin-susceptible Enterococcus faecalis JH2-2 conferred low-level vancomycin resistance only when d-Ser was present in the growth medium. The peptidoglycan precursor profiles of E. faecalis JH2-2 and JH2-2(pAT708) and JH2-2(pAT717) indicated that the function of VanXYC was hydrolysis of d-Ala-d-Ala and removal of d-Ala from UDP-MurNAc-pentapeptide[d-Ala]. VanC-1 and VanXYC were essential, but not sufficient, for vancomycin resistance.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2958.1999.01604.x
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  • 10
    Electronic Resource
    Electronic Resource
    Requirement of the VanY and VanX D,D-peptidases for glycopeptide resistance in enterococci (1998)
    Oxford BSL : Blackwell Publishing Ltd
    Molecular microbiology 30 (1998), S. 0 
    Details
    ISSN: 1365-2958
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Medicine
    Notes: Transposon Tn1546 confers resistance to glycopeptide antibiotics in enterococci and encodes two D,D-peptidases (VanX and VanY) in addition to the enzymes for the synthesis of D-alanyl-D-lactate (D-Ala-D-Lac). VanY was produced in the baculovirus expression system and purified as a proteolytic fragment that lacked the putative N-terminal membrane anchor of the protein. The enzyme was a Zn2+-dependent D,D-carboxypeptidase that cleaved the C-terminal residue of peptidoglycan precursors ending in R-D-Ala-D-Ala or R-D-Ala-D-Lac but not the dipeptide D-Ala-D-Ala. The specificity constants kcat/Km were 17- to 67-fold higher for substrates ending in the R-D-Ala-D-Ala target of glycopeptides. In Enterococcus faecalis, VanY was present in membrane and cytoplasmic fractions, produced UDP-MurNAc-tetrapeptide from cytoplasmic peptidoglycan precursors and was required for high-level glycopeptide resistance in a medium supplemented with D-Ala. The enzyme could not replace the VanX D,D-dipeptidase for the expression of glycopeptide resistance but a G237D substitution in the host D-Ala:D-Ala ligase restored resistance in a vanX null mutant. Deletion of the membrane anchor of VanY led to an active D,D-carboxypeptidase exclusively located in the cytoplasmic fraction that did not contribute to glycopeptide resistance in a D-Ala-containing medium. Thus, VanX and VanY had non-overlapping functions involving the hydrolysis of D-Ala-D-Ala and the removal of D-Ala from membrane-bound lipid intermediates respectively.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-2958.1998.01114.x
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