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P Leduc

Publications and source records attributed to P Leduc.

11 recordsLinked to original sources
PubMed2001

Clean oxidation of thiolates to sulfinates in a four-coordinate CoIII complex with a mixed carboxamido N-thiolato S donor set: relevance to nitrile hydratase.

A new [Co(N2(SO2)2)(CNtBu)2](Et4N) complex 6 was prepared from N,N'-(3-mercapto-3-methyl-butyryl)-o-phenylenediamine and completely characterized. While the starting square planar complex [Co(N2S2)](Et4N) 4 was destroyed by dioxirane, the Co ligated thiolates of the six-coordinate intermediate [Co(N2S2)(CNtBu)2](Et4N) complex 5 was readily oxidized to sulfinates with a stoichiometric amount of this oxidant. The resulting complex 6 crystallizes with an octahedral structure. The SO bonds of the SO2 groups are almost equivalent (approximately 1.483 and approximately 1.453 A). The isonitrile is linearly bonded to the cobalt with a Co-C-N angle of 177.5 degrees and a very short C-N(tBu) distance of 1.13 A, which has a triple bond character. As expected for six-coordinate CoIII complexes, 5 and 6 are diamagnetic in agreement with their 1H and 13C NMR spectra. The SO2 IR bands are located at 1210 cm(-1) (v(as)SO2) and 1070 cm(-1) (v(s)SO2), while the CN vibration of the isonitrile is observed at 2170 cm(-1) in 5 and 2210 cm(-1) in 6. Very recently, it has been reported in the literature that oxidation of the coordinated thiolates was required for activity of both Fe and Co nitrile hydratases. Complex 6, with two oxidized thiolates trans to two deprotonated carboxamido nitrogens, is the first to have an in-plane closely related to that of the Co-NHase active site.

Catalytic Domain↗
PubMed2000

Apoptosis of syncytia induced by the HIV-1-envelope glycoprotein complex: influence of cell shape and size.

Cells stably transfected with a lymphotropic HIV-1 Env gene form syncytia when cocultured with CD4(+)CXCR4(+) cells. Heterokaryons then spontaneously undergo apoptosis, while manifesting signs of mitochondrial membrane pemeabilization as well as nuclear chromatin condensation. Modulation of cellular geometry was achieved by growing syncytia on self-assembled monolayers of terminally substituted alkanethiolates designed to control the adhesive properties of the substrates. Spreading of syncytia, induced by culturing them on small circular adhesive islets (diameter 5 microm), placed at a distance that cells can bridge (10 microm), inhibited spontaneous and staurosporin-induced signs of apoptosis, both at the mitochondrial and at the nuclear levels, and allowed for the generation of larger syncytia. Transient cell spreading conferred a memory of apoptosis inhibition which was conserved upon adoption of a conventional cell shape. Limiting syncytium size by culturing them on square-shaped planar adhesive islands of defined size (400 to 2500 microm(2)), separated by nonadhesive regions, enhanced the rate of apoptotic cell death, as indicated by an accelerated permeabilization of the outer mitochondrial membrane, loss of the mitochondrial inner transmembrane potential, and an increased frequency of nuclear apoptosis. In conclusion, external constraints on syncytial size and shape strongly modulate their propensity to undergo apoptosis.

Apoptosis↗
PubMed2000

Toward model complexes of Co-containing nitrile hydratases: synthesis, complete characterization and reactivity toward ligands such as CN- and NO of the first square planar CoIII complex with two different carboxamido nitrogens and two thiolato sulfur donors.

A [CoIII(N2S2)]NEt4 complex, with two carboxamido nitrogens and two alkylthiolato sulfurs, was prepared from N,N'-(2-thioacetylisobutyryl)-2-aminobenzylamine, and characterized. It crystallizes with a distorted square planar structure including two short Co-N bonds (approximately 1.882 A) and two short Co-S bonds (approximately 2.134 A). The ligand defines an 11-atom chelate, which may be Co ligands in the mean plane of Co-containing nitrile hydratase. The CoIII oxidation state, reversibly reduced at -1.13 V (vs. SCE) and irreversibly oxidized at +1.29 V (vs. SCE) in DMF, is stable over a 2 V potential range. From the temperature dependence of its magnetic susceptibility, cobalt(III) was found to be in an S = 1 triplet ground state, in agreement with the broad resonances observed in its 1H-NMR spectrum. Preliminary spectral studies showed that this complex does not interact with imidazole, H2O or HO-, but binds two CN anions or two NO molecules. The IR spectrum of the dinitrosyl complex exhibits two NO stretches at 1765 and 1820 cm(-1), in the range previously observed for dinitrosylated complexes derived from cobalt(I). This result suggests that, similarly to Fe NHases, Co NHases might readily bind NO.

Cobalt↗
PubMed1997

Purification and characterization of extremely thermostable beta-mannanase, beta-mannosidase, and alpha-galactosidase from the hyperthermophilic eubacterium Thermotoga neapolitana 5068.

Thermostable and thermoactive beta-mannanase (1,4-beta-D-mannan mannanohydrolase [EC 3.2.1.78]), beta-mannosidase (beta-D-mannopyranoside hydrolase [EC 3.2.1.25]) and alpha-galactosidase (alpha-D-galactoside galactohydrolase [EC 3.2.1.22]) were purified to homogeneity from cell extracts and extracellular culture supernatants of the hyperthermophilic eubacterium Thermotoga neapolitana 5068 grown on guar gum-based media. The beta-mannanase was an extracellular monomeric enzyme with a molecular mass of 65 kDa. The optimal temperature for activity was 90 to 92 degrees C, with half-lives (t1/2) of 34 h at 85 degrees C, 13 h at 90 degrees C, and 35 min at 100 degrees C. The beta-mannosidase and alpha-galactosidase were found primarily in cell extracts. The beta-mannosidase was a homodimer consisting of approximately 100-kDa molecular mass subunits. The optimal temperature for activity was 87 degrees C, with t1/2 of 18 h at 85 degrees C, 42 min at 90 degrees C, and 2 min at 98 degrees C. The alpha-galactosidase was a 61-kDa monomeric enzyme with a temperature optimum of 100 to 103 degrees C and t1/2 of 9 h at 85 degrees C, 2 h at 90 degrees C, and 3 min at 100 degrees C. These enzymes represent the most thermostable and thermoactive versions of these types yet reported and probably act synergistically to hydrolyze extracellular galactomannans to monosaccharides by T. neapolitana for nutritional purposes. The significance of such substrates in geothermal environments remains to be seen.

Carbohydrate Sequence↗
PubMed1981

Aseptic loosening of cemented total arthroplasties of the hip in relation to positioning of the prosthesis. New utilization of the Tschuprow-Cramer statistical test.

A statistical study of 1200 McKee-Farrar cemented total prostheses of the hip demonstrated the importance of a horizontal position of the cup and a valgus position of the prosthetic stem, in avoiding aseptic loosening of the prosthetic parts. A new test (the Cramer test) showed that a statistical bond exists between the position of the prosthesis and the occurrence of aseptic loosening.

Bone Cements↗
PubMed1978

Structural studies of staphylococcal protease. III. Binding of anions to the spin-labeled enzyme.

The staphylococcal protease was coupled at the active-site serine residue with a spin-labeled analog of diisopropyl fluorophosphonate and the interaction of competitive inhibitors such as chloride and acetate anions, as well as N-carbobenzoxy-L-glutamic acid (Z-L-Glu), was investigated by electron paramagnetic resonance spectroscopy. It was observed that the addition of chloride ions to the spin-labeled enzyme increased the freedom of motion of the spin label while the presence of acetate ions and Z-L-Glu resulted in an increase in the immobilization of the spin label. These results suggest that these ions bind to the active site region in different ways.

Binding Sites↗
PubMed1975

Proton magnetic resonance titration curves of the three histidine residues of staphylococcal protease.

Proton magnetic resonance spectra of staphylococcal protease, a serine protease from Staphylococcus aureus, strain V8, are presented. Initial proton spectra were obtained at 220 MHz, and more detailed studies of the aromatic region were carried out by correlation spectroscopy at 250 MHz. The overall spectrum bears a close resemblance to one calculated from the sum of spectra of the component amino acids. Chemical shifts of the three tyrosine, four phenylalanine, and three histidine residues appear to be equivalent at pH 3.7 and 8.5 indicating that they are all in normal chemical environments in the enzyme. The staphylococcal protease contains a large number of slowly exchanging protons. In fact, interpretable spectra of the aromatic region were obtained only after extensive exchange of N-H groups with deuterium from the D2O solvent. Proton magnetic resonance titration studies of the three histidine residues indicate that these have normal chemical shifts and pK' values. When the data are fitted to single noninteracting titration curves, the histidine pK' values are 7.19 plus or minus 0.02, 6.85 plus or minus 0.03, and 6.69 plus or minus 0.02. The titration curves of two of the histidine residues indicate negative cooperativity. A possible explanation for this is a direct electrostatic interaction between the two histidines. The titration data for these histidines give a significantly better fit to such a mutual interaction model than to noninteracting titration curves. The component microscopic dissociation constants have been calculated. Mutual interaction leads to pK' displacements of 0.31 unit; which indicates a distance of approximately 7 angstrom between the two interacting histidine rings according to the model of Tanford and Roxby. The proton resonances of the two interacting histidines are doubled in the pH region 6.7-7.0 suggesting the presence of two forms of the enzyme having lifetimes in excess of 30 msec.

Amino Acids↗