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In this paper, a new method for the separation of noise categories based on Four-Wave Mixing is presented. The theoretical analysis is grounded in the Gaussian Noise model and verified by split step simulations. The noise categories react differently to the introduced perturbations, by performing a set of perturbations the behaviour of the different categories can be separated by means of a least-square fitting. Given ASE is independent of the induced perturbations, it is possible to separate noise contributions. The analysis includes constant and variable power perturbations. The estimation of the noise categories is discussed from two points of view: NSR evolution post-DSP processing, and over the power spectral density in a notched region. The NSR estimation can only be performed at reception, whereas the power spectral density approach can be performed along the optical link if a high resolution Optical Spectrum Analyzer is available. Additionally, we perform a simple experimental verification considering of two WaveLogic 3 transceivers for the NSR, successfully estimating the nonlinear noise contributions.

Context.The infrared wide-field camera (WFCAM) is now in operation on the 3.8 m UK Infrared Telescope on Mauna Kea. WFCAM currently has the fastest survey speed of any infrared camera in the world, and combined with generous allocations of telescope time, will produce deep maps of the sky from Zto Kband. The data from a set of public surveys, known as UKIDSS, will be initially available to astronomers in ESO member states, and later to the world.

Many hearing aids can identify different acoustic scenes and adjust the frequency-dependent gains according to the detected scene. This study compared loudness and tone-quality ratings for sounds processed via a simulated five-channel compression hearing aid fitted using NAL-NL2 or using a modification of the fitting designed to be appropriate for the type of acoustic scene: speech in quiet, speech in noise, music, and noise alone. The results suggest that there may be small benefits of modifying gains for different acoustic scenes. The optimal modification for music appears to be less than that used in this study.

This study was designed to examine whether age-related differences in melodic pitch perception may be mediated by temporal processing. Temporal models of pitch suggest that performance will decline as the lowest component of a complex tone increases in frequency, regardless of age. In addition, if there are age-related deficits in temporal processing in older adults, this group may have reduced performance relative to younger adults even in the most favorable conditions.

Derivatives of thymidine containing o-carboranylalkyl groups at the N-3 position and derivatives of 2‘-deoxyuridine containing o-carboranylalkylmercapto groups at the C-5 position were synthesized. The alkyl spacers consist of 4−8 methylene units. The synthesis of the former compounds required 3−4 reaction steps in up to 75% overall yield and that of the latter 9−10 reaction steps with significantly lower overall yield. Derivatives of thymidine substituted with carboranylalkyl substituents at the N-3 position and short spacers were phosphorylated by both recombinant and purified cytosolic thymidine kinase (TK1) to a relatively high degree. None of the tested 2‘-deoxyuridine derivatives possessing carboranyl substituents at the C-5 position were phosphorylated by either recombinant or purified TK1. The amounts of phosphorylation product detected for some of the C-5-substituted nucleosides with recombinant mitochondrial thymidine kinase (TK2) were low but significant and decreased with increasing lengths of the alkyl spacer. The data obtained in this study do not seem to support the tether concept applied in the synthesis of the new C-5- and N-3-substituted carboranyl nucleosides intended to reduce possible steric interference in the binding of carboranyl nucleosides with deoxynucleoside kinases. Instead, it appeared that a closer proximity of the bulky carborane moiety to the nucleoside scaffold resulted in better substrate characteristics.

Lactobacillus acidophilus R-26 a strain deficient in ribonucleotide reductase, was grown with [G-14C]deoxycytidine as the only source of deoxyribose in the medium. Of the radioactivity incorporated into deoxyribonucleic acid, a fifth moved directly into deoxyribonucleic acid deoxycytidylate, without deamination. Furthermore, deoxycytidine and thymidine nucleotides had similar sugar/base ratios, suggesting a direct conversion of deoxycytidine nucleotides to thymidine nucleotides through deamination, without further dilution by glycosyl transfer. Although radioactivity was incorporated into both the sugar and base moieties of deoxyribonucleic acid pyrimidine deoxyribonucleotides, only the sugar moiety of purine deoxyribonucleotides was labeled. Purine deoxyribonucleotides probably were synthesized by glycosyl transfer from [G-14C]deoxycytidine to unlabeled purines, followed by phosphorylation of the deoxynucleotides.

Trends in coronary heart disease mortality and sudden death were studied in 35- to 44-year-old white male residents of Allegheny County, Pennsylvania. Deaths coded as any cardiac or vascular disease, diabetes, unexplained sudden death, and other rubrics were eligible for investigation, and the cause of death was validated by physicians examining multiple data sources about the deaths. During 1970-1990, 1,424 white male deaths were investigated, with 903 validated as coronary heart disease. In that time span, white male coronary heart disease mortality fell from 93.4 to 36.7 per 100,000 population per year, a 60% decline. Little proportionate change was seen in characteristics of the deaths, which were predominantly sudden and out-of-hospital. Diabetes mellitus history increased proportionately over time, largely because diabetics' mortality rates, unlike those of all other subgroups, did not fall. These observations support the contention that the decline in coronary heart disease mortality relates to risk factor modification more than to improvements in the treatment of coronary heart disease. Differences in death certification practices must be considered when interpreting and comparing vital statistics data.

The heterodimeric subunits of deoxyadenosine kinase (dAK)-deoxyguanosine kinase (dGK) from Lactobacillus acidophilus R-26 exhibit contrasting conformations manifested in the nearly unidirectional heterotropic activation of dAK when dGK binds deoxyguanosine. This is mediated, in part, by the conserved Ras switch I-like sequence (residues 153-161) [Guo et al. (1997) J. Biol. Chem. 272, 6890-6897]. In an attempt to identify domains differentiating the specificities of dAK and dGK, we constructed several chimeras splicing heterodimeric dAK within this region. In Chimera-III, dAK residues 120-170 were replaced by the homologous section of dGK. dAK activity was elevated 40%, but although it retained its original specificity and Km values, it could no longer be activated by deoxyguanosine. Moreover, both the activated dAK and the "dAK" of Chimera-III exhibited (i) an increased Ks for the leading substrate ATP-Mg2+, suggesting the formation of intermediate enzyme species along their respective kinetic pathways, and (ii) broadened and lower pH optima for the dAK activities. These observations further indicate the importance of dAK residues 120-170, including the Ras-like segment, in catalysis and heterotropic activation. The other conformational properties of dAK (e.g. self-inactivity and MgATP being the leading substrate) were unaltered by this substitution, thus localizing the responsible domains even further upstream.

Because of its structural similarity to polyunsaturated fatty acids, anandamide could serve as substrate for enzymes such as lipoxygenases and cyclooxygenases, which metabolize polyunsaturated fatty acids to potent bioactive metabolites. Here the ability of recombinant human cyclooxygenase-1 (hCOX-1) and cyclooxygenase-2 (hCOX-2) to metabolize anandamide was studied. Baculovirus-expressed and -purified hCOX-2, but not hCOX-1, effectively oxygenated anandamide. Reverse phase high pressure liquid chromatography analysis of the products derived from 1-14C-labeled anandamide showed that the products formed are similar to those formed with arachidonic acid as substrate. The major prostanoid product derived from anandamide was determined by mass spectrometry to be prostaglandin E2 ethanolamide. Incubation of anandamide with lysates and the intact cell line expressing COX-2 but not that of COX-1 produced prostaglandin E2 ethanolamide. These results demonstrate the existence of a COX-2-mediated pathway for anandamide metabolism, and the metabolites formed represent a novel class of prostaglandins.

Comparative inhibition kinetics with natural dNTP end products (dNp3) and new synthetic bisubstrate-type analogs, dNp4A (deoxynucleoside 5'-adenosine 5'''-P1,P4-tetraphosphate), have been studied with their target deoxynucleoside kinases from Lactobacillus acidophilus. Analysis of inhibition specificity, inhibition patterns, and Ki(app) under various conditions has revealed the following conclusions. Both dNTP and dNp4A bind to the active site of the corresponding kinase through multiple binding determinants. The deoxynucleoside moiety of dNTP fits optimally at the deoxynucleoside binding site and provides the basis for its inhibition specificity, whereas the triphosphate group interacts with the ATP binding site, reinforcing the affinity of the molecule as a potent end product inhibitor (Ki = 0.4-3 microM). The adenosine moiety of dNp4A does not contribute to the binding of this compound, whereas the tetraphosphate portion is the second binding determinant, just as in the model developed for dNTP. dNTP and dNp4A proved to be useful tools for distinguishing the kinetic mechanisms of kinases which follow sequential pathways, i.e. the rapid equilibrium Random Bi Bi for dCyd and dGuo kinases and the steady state Ordered Bi Bi mechanism for two dAdo kinases associated either with dCyd kinase or with dGuo kinase on different multifunctional proteins.

A nucleoside phosphotransferase has been purified to homogeneity from barley seedlings. Its Mr is about 50,000 and it consists of two subunits of equal size. A tightly bound metal ion required for activity can be replaced by Mg, Ba, or Co ions, but not by divalent Cu, Ca, Cd, or Hg. The enzyme is capable of catalyzing the transfer of phosphate from nucleoside monophosphates to the 5'-hydroxyl of any other nucleoside, but shows a decided preference for purine deoxynucleoside phosphate acceptors. A short lived phosphoryl enzyme intermediate has been trapped by rapid denaturation in presence of [32P]AMP. The steady state kinetics of this enzyme is found to be fully consistent with a branched ping pong pathway involving a compulsory phosphoryl enzyme intermediate from which phosphate may be transferred to nucleoside or to water. With appropriately chosen substrates, parallel line reciprocal plots were obtained, provided that both products of the branched pathway were taken into account in the rate measurements. Conversely, when only transphosphorylation was measured, converging reciprocal plots were obtained. Accordingly, assays were devised for the measurement of three velocity components: transphosphorylation, hydrolysis, and the sum of both reactions. Competitive inhibition of the transferase reaction by higher concentrations of either substrate is attributed to deadend interactions. Instead of being inhibited by the formation of a putative E-P.AMP complex, however, the phosphatase reaction is accelerated almost 2-fold.

Deoxyadenosine kinase (dAK) forms a heterodimer with either deoxyguanosine kinase (dGK) or deoxycytidine kinase (dCK), and is heterotropically activated 3-5 times by dGuo or dCyd. Expressed alone, dAK is inactive and exhibits no response to dGuo or dCyd; activity and heterotropic response are fully restored upon reassociation with dGK or dCK. However, turnover of independently expressed dGK or dCK is nearly maximal, being further activated only 50-100% upon reassociation with dAK. In neither case is the heterotropic activation due to ligand-induced heterodimer formation. A proline/alanine substitution within a dAK segment homologous to loop G2 of Ras proteins yielded a heterodimer with dAK permanently cis-activated 2-fold, with a corresponding reduction in heterotropic activation by dGuo. A chimeric dAK, with 25% of its C terminus substituted by the homologous sequence from dGK, was inactive alone, and its characteristics were unchanged in the reconstituted heterodimer. Superimposing the Pro/Ala substitution on this chimera also reduced heterotropic activation by half. Cross-linking the dimer by 1,5-difluoro-2,4-dinitrobenzene was inhibited by ATP, dATP, dGTP, and dAdo, suggesting the proximity of the active site(s) to the interface. These data suggest that dAK depends on dGK or dCK in a manner resembling the reliance of Ras upon GTPase activating protein.

New multisubstrate-type inhibitors of the deoxynucleoside kinases have been synthesized, tested for their specificity as soluble inhibitors of enzymes from Lactobacillus acidophilus, and used to construct media for affinity chromatography. Each inhibitor was a deoxynucleoside 5'-adenosine 5“'-P1,P4-tetraphosphate (abbreviated dNp4A, where dN represents a dAdo, dCyd, dGuo, or dThd moiety linked through its 5'-hydroxyl to the terminal phosphate of adenosine tetraphosphate). At micromolar concentrations, each inhibitor strongly and specifically inhibited the corresponding deoxynucleoside kinase. Each of the four Lactobacillus deoxynucleoside kinase activities was selectively retained on its homologous dNp4A-Sepharose affinity medium. The activity was eluted on addition of the respective dNp4A with up to 70% recovery and 300-500-fold purification (relative to an ammonium sulfate fraction). Whereas dThd kinase was retained only by the dTp4A column, a portion of the dAdo kinase activity was retained, along with all the dCyd kinase or dGuo kinase, on dCp4A- or dGp4A-Sepharose, respectively, and coeluted with these activities. Conversely, all three activities were quantitatively retained on dAp4A-Sepharose, without competition from either dCyd or dGuo, and were eluted simultaneously upon addition of dAp4A. These observations further confirm the understanding that this organism employs paired, and presumably bifunctional, kinases, namely dCyd/dAdo kinase and dGuo/dAdo kinase, along with a separate thymidine kinase.

Previous work conducted on hybrid journal bearings has shown that a combination of hydrostatic and hydrodynamic lubrication principles leads to good load support over a wide range of speeds, including zero speed. Above the transition speed, particularly with large bearing diameters or low-viscosity lubricants, the mode of flow within the fluid film degenerates from that of pure laminar flow, through a transitional or vortex flow regime, to fully developed turbulent flow. This work presents a theoretical investigation of slot entry hybrid journal bearings operating in the superlaminar flow regimes. In particular, the work considers the effects of superlaminar flow on the optimization of slot entry hybrid journal bearings.

Examination of conserved motifs on the cloned subunits of the deoxyguanosine kinase/deoxyadenosine kinase (dGK/dAK) of Lactobacillus acidophilus R-26 has begun with the Asp-Arg-Ser (DRS) motif. Replacement of Asp-78 of both subunits with Glu, Ala, or Asn reduced dGK and dAK activities to less than 0.2%, whereas replacement of Arg-79 with Lys, either on both subunits in tandem (R79K), or on the dGK subunit only (R79K:dGK), yielded active but kinetically modified enzymes. These were partially purified, and their kinetic and regulatory properties were analyzed. For dAK activity, the Vmax of the R79K:dGK enzyme was increased 28-fold, with no change in the limiting Km for dAdo, but with a slightly reduced Km for MgATP. The V/K efficiency ratio of dAK was also increased 29-fold, but that of dGK was decreased to 5-10% due to a 10-fold increase in Km for dGuo and a reduced Vmax. Therefore, the R79K substitution seems to have a greater effect on dGuo binding than on that of dAdo, but dGK modification appears to produce a stimulatory conformational effect on the opposite subunit, resembling the known unidirectional activation of dAK by either dGuo or dGTP.

Two uniquely paired deoxynucleoside kinases, deoxycytidine kinase/deoxyadenosine kinase (dCK/dAK) and deoxyguanosine kinase/deoxyadenosine kinase (dGK/dAK) are required, together with thymidine kinase (TK), for deoxynucleotide synthesis in Lactobacillus acidophilus R-26. Using polymerase chain reaction-generated probes based on N-terminal amino acid sequences, we have cloned tandem genes for 25- and 26-kDa polypeptides, whose derived amino acid sequences and size correspond to wild-type Lactobacillus enzyme subunits. Expression in Escherichia coli uses a single endogenous promoter and yields active dGK/dAK (approximately 3% of extracted protein) closely resembling wild-type dGK/dAK in specificity, kinetics, heterotropic activation, and end product inhibition. Alignment of cloned genes reveals 65% identity in their DNA sequences and 61% identity in derived amino acid sequences. Comparison with herpes-viral TKs reveals three conserved regions: glycine- and arginine-rich ATP-binding motifs and a D/E-R-S/H motif at the putative TK deoxynucleoside site. Greater homology, however, is seen upon multiple alignment of dGK with mammalian deoxycytidine kinases, yielding the consensus sequence-D/E-R-S-I/V-Y-x-D-.dGK also shares a sequence (-Y-D-P-T-I/L-E-D-S/Y-Y-) required for GTP hydrolysis by p21ras.

Peat moss (Sphagnum) from the surface of an Atlantic peat bog has been extracted with a mixture of benzene and ethanol. The extract has been fractionated chromatographically on alumina. A mixture of sterols has been isolated from one fraction. This mixture has been proved by oxidation experiments to consist of β-sitostanol (stigmastanol) and β-sitosterol. It constituted approximately 0.2% by weight of the dried peat moss.

A brief account is given of experiments in which gold electrodes, as a result of thermal deactivation in hydrogen, change from a state in which their behavior in relation to the hydrogen evolution reaction is normal to a state characterized by high positive rest potentials, greatly enhanced overpotentials which increase progressively during current flow, and which decay slowly on open circuit, generating potential–time curves which resemble desorption isotherms.Conclusions based on these phenomena are supported by the results of experiments with poisoned platinum electrodes, which not only behave similarly but are also shown to retain reducing power for a limited time on open circuit.It is suggested that electrodeposited hydrogen atoms may sometimes evaporate from an electrode into solution by a mechanism involving the participation of molecule-ions. A recent theoretical treatment of hydrogen overpotential can be extended to allow for the occurrence of such a final reaction step.

By further chromatographic fractionation of the unsaponifiable matter from an extract of peat moss (Sphagnum) three crystalline triterpenes have been isolated. They have been identified as α-amyrin, taraxerone, and taraxerol by their physical and chemical properties.

An adaptation of an electrolytic method is suggested for the removal of protecting groups in peptide chemistry. Some initial experiments are reported indicating the scope and possible limitations of the method.

This communication reports the synthesis of oxytocin using the Merrifield solid phase technique. For the synthesis both the o-nitrophenyl sulfenyl and t-butyloxycarbonyl blocking groups were used for masking the amino function. The oxytocin precursor obtained gave the same yield of hormone when subjected to the usual procedures as that obtained from a nonapeptide synthesized by conventional methods.

A STUDY has been made of the effect of low concentrations of n-aliphatic alcohols on the interfacial tension of water against hexane and octane. For this purpose an apparatus was designed, based on the drop-volume method, which allowed the interfacial tension to be measured with an accuracy of 0.04 dyne cm.−1in rigorously purified systems. Determinations were carried out at 10°, 25° and 40° C.

WITH the object of throwing light on the mechanism of three-carbon tautomerism, we have studied the equilibration of vinylacetic and crotonic acids in the presence of 1.05 mols of sodium hydroxide in dilute ‘heavy water’ at 100° C. As a check, we have also examined the behaviour of butyric acid under the same conditions. The isotopic ratio in both the recovered solvent and the water obtained by combustion of the residual sodium salts has been determined by a flotation method accurate to one part per million of density; the necessary purifications were carried out without loss of water, thus avoiding the possibility of isotopic fractionation.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

THE silver/silver chloride electrode has been preferred to the calomel electrode for precise potentiometric work, and E0for the cell H2, ∣ Pt ∣ HCl(aq.) ∣ Hg2Cl2∣ Hg has not been directly determined with any degree of accuracy. Nevertheless, mercury suffers from none of the difficulties associated with purity and thermal or mechanical history which affect silver and other hard metals. Attempts have been made to remedy the defects of the calomel electrode in order to make use of this advantage, and have been so far successful as to warrant a preliminary report.

THE hydrogen electrode is the primary standard to which all electrode potentials are referred and is used in cells without liquid junction for measurements of high accuracy. The potential of the hydrogen electrode is corrected to the standard pressure of one atmosphere on the basis that the electrode is in equilibrium with the measured partial pressure of hydrogen above the solution. It is, however, not the gas phase which directly determines the potential, but the hydrogen in solution; and a tacit assumption that the concentration of dissolved hydrogen is unequivocally defined by the gas pressure is false. This error can arise in two ways.