Speech intelligibility normally declines at high intensities, but this "rollover" effect decreases when steep filtering reduces sentences to an array of rectangular subcritical bands. The present ...study found that interpolating low intensity noise between the speech bands further decreases rollover, supporting the hypothesis that rollover is normally reduced by lateral inhibition of input from rate-saturated auditory nerve fibers. With noise also present within the speech (a 15 dB signal-to-noise ratio) an array of 6%-wide speech bands with interpolated noise was found to be 9% more intelligible at 100 dB than a spectrally continuous band of speech covering the same frequency range.
Polyhydroxybutyrate (PHB) synthases (polymerases) catalyze the polymerization of the coenzyme A thioester of 3-hydroxybutyrate to PHB. The Ralstonia eutropha PHB synthase purified from recombinant E. ...coli cells exists in aqueous solution in both monomeric (single subunit) and homodimeric (two subunits) forms in equilibrium. Several lines of evidence suggest that the homodimer is the active form of the synthase. The initial mechanistic model for the polymerization reaction proposed that two different thiol groups form the catalytic site. The cysteine at 319 has been shown to provide one thiol group that is involved in the covalent catalysis, but a second thiol group on the same protein molecule has not yet been identified. It is suggested that cysteines at 319 from each of the two molecules of a homodimer synthase provide two identical thiol groups to jointly form a single catalytic site. To verify this model using the strategy of in vitro reconstitution, heterodimers composed of the wild-type subunit and of the C(319) mutated subunit were constructed and the activities at various ratios of the wild-type subunit to the mutated subunit were measured. The experimental results indicate that the homodimer is the active form of the enzyme, that the heterodimer containing the mutated subunit has no activity, and that a single cysteine is not sufficient for catalysis. Two identical thiol groups from C(319) residues on each subunit of the homodimer are required to form the catalytic site for the initiation and propagation reactions. We further demonstrate that a dimer synthase that has initiated the polymerization reaction (primed synthase) is significantly more stable against dissociation than the unprimed (unreacted) dimer synthase. These two properties explain the nature of lag phenomenon during the in vitro polymerization reaction catalyzed by this enzyme
The bacteria Pseudomonas oleovorans, P. resinovorans, P. putida, and P. citronellolis were evaluated for their ability to grow and produce poly(hydroxyalkanoates) (PHA) using tallow free fatty acids ...and tallow triglyceride as carbon substrates. Tallow free fatty acids supported cell growth and PHA production for all four organisms, yielding PHA contents of 18%, 15%, 19% and 3% of their cell dry weights for P. oleovorans, P. resinovorans, P. putida, and P. citronellolis respectively. Only P. resinovorans, however, was able to grow and produce PHA polymer, with cells attaining a PHA content of 15% of their cell dry weight, using unhydrolyzed tallow as the substrate. Extracts from 46-h cultures of P. resinovorans were found to have a higher esterase activity (12.80 units microliters-1 min-1) compared to the activities found for cultures of P. oleovorans, P. citronellolis, and P. putida (< 0.03 units microliters-1 min-1). Polymer repeat-unit compositions were determined by GC analysis of the beta-hydroxymethyl esters of hydrolyzed PHA, and ranged in carbon-chain lengths from C4 to C14, with some mono-unsaturation in the C12 and C14 side-chains. PHA compositions were similar for the polymers obtained from all four organisms, with repeat units of chain lengths C8 and C10 predominating.
Using organically synthesized hydroxyalkanoate coenzyme A thioesters, the activities of two short-chain polyhydroxalkanoate (PHA) synthases were investigated--Ralstonia eutropha PHA synthase (a type ...I PHA synthase) and Ectothiorhodospira shaposhnikovii PHA synthase (a type III synthase). The results indicate that the two synthases have similar activities towards most of the monomers tested. 3-Hydroxybutyryl CoA was found to be the most efficient substrate for both synthases. Changes in the side-chain length of the monomers affect monomer reactivity, with shortening of the side-chain length having the more severe effect. Hydrophobicity in the side chain appears to play an important role in the catalytic reaction. The configuration and the position of the hydroxyl group also affect the reactivity of a monomer. Monomers with the S configuration can not be recognized by either synthase. Moving the hydroxyl group from the beta carbon to the alpha carbon has a much more severe effect on the reactivity of the monomer than moving the hydroxyl group to the gamma carbon. The results demonstrate that the in vitro system can be used to prepare entirely novel polymers that may not be obtainable from living cells because of metabolic restrictions.
The aim of the present work is the investigation of the structural, mechanical and tribological properties of low-wear diamond-like carbon (DLC) coatings for industrial applications. Amorphous ...hydrogen-free (a-C) and hydrogenated (a-C:H) DLC coatings were coated onto various steel substrates (AISI 1045H, B7, H13, D2, M2) with hardness levels varying from 28 to 66 HRC, by employing the pulsed laser deposition (PLD) method. Therefore, graphite targets were ablated with the 1064 nm wavelength of an Nd:YAG laser in argon and C
2H
2 atmospheres. The high mean laser power of the applied PLD equipment guarantees deposition rates competitive to other physical vapour deposition (PVD) techniques. Because of the specific process conditions and the use of pure titanium adhesive interface layers, coatings with high adhesion to the substrates were produced at room temperature. The investigations of the coatings by means of light and scanning electron microscopy reveals the high surface quality and extremely dense coating structures. XRD measurements indicated the amorphous structure of the coatings. The nature of the chemical bonding was examined by XPS, indicating different amounts of sp
3 carbon bonds. Pin-on-disc tests against 100Cr6 ball-bearing steel balls as counterparts show an excellent wear resistance of a-C and a-C:H DLC coatings on all different steel substrates. These results, demonstrated the applicability of PLD–DLC coatings for wear protection of high precision components in the field of tools and mechanical components.
Poly(3-hydroxyoctanoate-co-3-hydroxy-10-undecenoate)s (PHOUs) with controlled amounts of unsaturated side chains were produced by Pseudomonas oleovorans from various mixtures of 10-undecenoic acid ...and octanoic acid. Epoxidation of the unsaturated side chains in PHOU, by reacting the polymer with m-chloroperbenzoic acid (MCPBA) in homogeneous solution, was readily carried out. After complete epoxidation, changes in the molecular weights and thermal transitions of the PHOUs were investigated by gel permeation chromatography (GPC) and differential scanning calorimetry (DSC), respectively, and the thermal stabilities of the initial and epoxidized polymers were measured by thermogravimetric analysis (TGA). The acidic conditions used for the epoxidation reaction did not result in a significant decrease in molecular weight of the PHOUs. The epoxidized PHOUs were completely soluble, indicating that cross-linking did not occur, but transformation of the vinyl groups in PHOU into epoxide groups caused a decrease in the melting temperature and the enthalpy of melting. In contrast, the glass transition temperatures increased in a linear manner with epoxide group content in the product polymer, and the thermal degradation behavior of the epoxidized polymer was considerably different from that of the initial polymer.
We succeeded in developing of a new method for in vitro poly(3-hydroxybutyrate) (P(3HB)) synthesis with coenzyme A (CoA) recycling. Thiophenyl (R)-3-hydroxybutyrate was used as a precursor for the ...monomer, (R)-3-hydroxybutylCoA ((R)-3HBCoA). The (R)-3HBCoA was synthesized by the ester exchange reaction between thiophenyl (R)-3-hydroxybutyrate and CoA. Although the polymerization reaction in the buffer (water phase) was performed, the reaction did not occurred. The results of a PHA synthase assay in the presence of thiophenol suggested that the reaction was inhibited by a small amount of thiophenol. To avoid the inhibition of PHA synthase by thiophenol, a water−organic solvent two-phase reaction system was developed for the polymerization reaction. The water−organic solvent two-phase reaction system has been used previously for the bioconversion of substrates with low solubility in water; it was used to remove thiophenol released during the ester exchange reaction from the water phase. Thiophenyl (R)-3-hydroxybutyrate and PHA synthase were dissolved in the organic solvent and water phases, respectively. Ester exchange between thiophenol and CoA occurs at the interface of water and the organic solvent phase, and the (R)-3HB 3-hydroxybutylCoA synthesized was polymerized sequentially by PhaC. The organic solvents with high a logP ow of more than 3.9 such as hexane, octane, decane, or dodecane were found to be suitable for the organic solvent phase in the two-phase system. The polymerization reaction mixture showed signs of turbidity in 2 h, after which white precipitates formed. The structural analyses by 1H NMR spectroscopy indicated that the product was P(3HB). The weight-averaged molecular weight and molecular weight distribution of P(3HB) synthesized were found to be 1.6 × 106 and 2.9, respectively. The maximum yield of P(3HB) based on thiophenyl (R)-3-hydroxybutyrate was 47%.
A novel copolymer that consisted of 3-hydroxyvalerate and 4-hydroxybutyrate, P(3HV-co-4HB), was synthesized in Hydrogenophaga pseudoflava by growing it in media containing γ-valerolactone and ...γ-butyrolactone as a carbon source. The monomer ratio in the copolymer was changed by altering the feed ratio of the two lactones. The cultivation technique was composed of three steps: the first-step for high cell production in Luria−Bertani medium, the second-step for intracellular degrading removal of poly(3-hydroxybutyrate) (P(3HB)), which was formed in the first step, by culturing the cells in carbon-source-free medium, and the final step for accumulation of P(3HV-co-4HB) in a mixed lactone medium. All the P(3HV-co-4HB) copolymers contained less than 1 mol % of 3HB unit. These copolymers were characterized by NMR spectroscopy, differential scanning calorimetry, wide-angle X-ray diffraction, and first-order kinetic analysis of intracellular degradation. The copolymer with an approximately equal ratio of the comonomers was found amorphous. The NMR microstructural analysis showed that the copolymers contained appreciable amounts of 3HV-rich or 4HB-rich chains. The 13C NMR splitting patterns associated with the four carbons in the 4HB unit of P(3HV-co-4HB) bear close resemblance to those observed in the 4HB unit of P(3HB-co-4HB). The signals arising from the carbons in the 3HV unit of P(3HV-co-4HB) split in a manner similar to those in the 3HB unit of P(3HB-co-4HB). Thus the sequences were assigned by comparing the NMR splittings for P(3HV-co-4HB) with those for P(3HB-co-4HB) and P(3HB-co-3HV). The sequence assignment was further checked by comparing the signal intensities before and after degradation of the copolymers. This was considered reasonable because the H. pseudoflava intracellular PHA depolymerase is more specific to the 3HV unit than to the 4HB unit, which was also confirmed by the higher degradation rate constant for the 3HV unit in the first-order kinetic analysis.
Neurokinin A (NKA) causes bronchoconstriction in asthmatic patients. In vitro both NK
1 and NK
2 receptors can mediate airway contraction. Moreover in guinea pigs, NK
3 receptors facilitate ...cholinergic neurotransmission. Dual tachykinin NK
1/NK
2 receptor antagonism results in prevention of NKA-induced bronchoconstriction. We have now examined the effect of a single dose of the triple tachykinin receptor antagonist CS-003 on NKA-induced bronchoconstriction in asthmatics.
A double blind, crossover, placebo-controlled trial in 16 mild asthmatics was performed. One single dose of CS-003 (200
mg, solution in distilled water) or matched placebo was given orally on the assessment days. NKA-provocation tests were performed pre-dose and 1, 8 and 24
h after dosing.
There was a significant shift to the right of the dose–response curve at 1 and 8
h after intake of CS-003. PC
20 was not reached in 12/16 patients at 1
h post-dose and in 5/16 patients at 8
h post-dose. This did not occur under placebo treatment.
A single dose of 200
mg CS-003 protected significantly against NKA-induced bronchoconstriction at 1 and 8
h post-dose in mild asthmatics.
PDF
