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PubMed1991

Electro-olfactogram and multiunit olfactory receptor responses to complex mixtures of amino acids in the channel catfish, Ictalurus punctatus.

In vivo electrophysiological recordings from populations of olfactory receptor neurons in the channel catfish, Ictalurus punctatus, clearly showed that both electro-olfactogram and integrated neural responses of olfactory receptor cells to complex mixtures consisting of up to 10 different amino acids were predictable with knowledge of (a) the responses to the individual components in the mixture and (b) the relative independence of the respective receptor sites for the component stimuli. All amino acid stimuli used to form the various mixtures were initially adjusted in concentration to provide approximately equal response magnitudes. Olfactory receptor responses to both multimixtures and binary mixtures were recorded. Multimixtures were formed by mixing equal aliquots of 3-10 different amino acids. Binary mixtures were formed by mixing equal aliquots of two equally stimulatory solutions. Solution 1 contained either one to nine different neutral amino acids with long side-chains (LCNs) or one to five different neutral amino acids with short side-chains (SCNs). Solution 2, comprising the binary mixture, consisted of only a single stimulus, either a LCN, SCN, basic, or acidic amino acid. The increasing magnitude of the olfactory receptor responses to mixtures consisting of an increasing number of neutral amino acids indicated that multiple receptor site types with highly overlapping specificities exist to these compounds. For both binary mixtures and multimixtures composed of neutral and basic or neutral and acidic amino acids, the receptor responses were significantly enhanced compared with those mixtures consisting of an equal number of only neutral amino acids. These results demonstrate that receptor sites for the basic and acidic amino acids, respectively, are highly independent of those for the neutral amino acids, and suggest that a mechanism for synergism is the simultaneous activation of relatively independent receptor sites by the components in the mixture. In contrast, there was no evidence for the occurrence of mixture suppression.

Amino Acids↗

PubMed1987

The equiratio taste mixture model successfully predicts the sensory response to the sweetness intensity of complex mixtures of sugars and sugar alcohols.

The equiratio taste mixture model was originally developed for the prediction of psychophysical power functions of equiratio mixtures of substances that have a similar taste and that also exhibit mutual cross adaptation. Earlier studies have shown that the model is valid for mixtures of sugars and/or sugar alcohols. Two experiments are reported in which it is questioned whether the psychophysical functions of mixtures of higher physical complexity can be predicted by the model. In the first experiment the psychophysical power functions of binary and quaternary equiratio mixture types were determined experimentally and compared to those predicted by the generalized model. In the second, similar, experiment quaternary and eight-component mixture types were examined. The method of magnitude estimation, in combination with the sip and spit procedure, was used. The functions predicted by the model were almost identical to the functions established on the basis of the experimental data. These results reconfirm that the gustatory modality operates like an 'averaging' system when processing this kind of mixture. It is argued that for other kind of mixtures the model will predict incorrectly. The status of the equiratio mixture model is discussed.

Adolescent↗

PubMed1987

A new approach for using short-term tests to screen complex mixtures.

This paper suggests a framework for developing parsimonious batteries of rapid, inexpensive biological assays which provide quantifiable estimates of human risk. The framework for the statistical design is tier testing. The framework develops an unusual perspective for using chemical spiking to evaluate the toxicity of a complex mixture to a battery of bioassays. This framework allows immediate evaluation of hazardous wastes and identifies important problems to provide focus for basic research.

Animals↗

PubMed1998

Simplified procedure for fractionation and structural characterisation of complex mixtures of N-linked glycans, released from HIV-1 gp120 and other highly glycosylated viral proteins.

HIV-1 gp120 is heavily glycosylated containing 24 N-glycosylation sites, and this makes elucidation of the significance of glycans at individual glycosylation sites a difficult task. A procedure is described where a complex mixture of biologically radiolabelled glycans of gp120, derived from a relatively small number of virus-infected cells may be characterized by a combination of N-glycanase release, single lectin separation, and normal phase HPLC (NP-HPLC). The method was applied in analysis of three N-linked glycosylation sites essential for the in vivo priming of T-cells, specific for an epitope in their vicinity (Sjölander, S., Bolmstedt, A., Akerblom, 1996. Virology 215, 124-133.). The carbohydrate compositions of wild type gp120 and of mutant variants gp120 lacking one, two, or all of these three active N-linked glycans were analysed. Cells were infected with r-vaccinia virus expressing wild-type gp120 or mutated gp120, or were infected with HIV-1BRU (wild type) or mutant virus variants. HIV-1 glycoproteins were purified by immunosorbent affinity chromatography and released glycans were separated on lectins, then analysed with NP-HPLC. Our data showed that the structural composition of glycans occupying two of the three glycosylation sites was heterogeneous but the site located adjacent to the T-cell epitope was equipped with one large, high mannose-type structure (> 11 units) with the capacity to cover a substantial part of the gp120 surface.

Carbohydrate Conformation↗

PubMed2000

High-resolution LC/MS for analysis of minor components in complex mixtures: negative ion ESI for identification of impurities and degradation products of a novel oligosaccharide antibiotic.

High-resolution mass spectrometry has been routinely used for structural confirmation and identification; however, it has mostly been applied to relatively pure samples. Exact mass measurement of minor components such as impurities, degradation products or metabolites in complex mixtures has been difficult without prior separation and isolation. Here we report the utilization of on-line liquid chromatography in combination with high-resolution mass spectrometry for the identification of impurities and base degradation products of Sch 27899, a member of the everninomicin class of antibiotics. Nine Sch 27899-related impurities and degradation products were detected by negative ion electrospray ionization using a magnetic sector mass spectrometer. Exact mass measurements were obtained at a resolution of 5000 using polyethylene glycol (PEG) sulfates as internal standards. Corresponding elemental compositions were determined within a 2 ppm error tolerance and structures were proposed for all components.

Aminoglycosides↗

PubMedDate not supplied

Influence of the microsomal inducer and the incubation system on mutagenicity of complex mixtures.

The mutagenicity of SRM 1649 and 1650 was tested in the presence of rat liver S9 mix which was induced by polychlorinated biphenyl (PCB) or by the combination of phenobarbital and 5,6-benzoflavone. The S9 mix induced by PCB activated benzo[a]pyrene strongly. The S9 mix induced by phenobarbital-5,6-benzoflavone activated the complex mixtures to approximately the same extent as that induced by PCB. This finding indicates that phenobarbital-5,6-benzoflavone instead of PCB may be suitable as an inducer under some conditions. The preincubation procedure for the mutagenicity test was performed by preincubating the test compound, S9 mix and bacteria for 20 min in a water bath. This procedure was as effective as the plate incorporation test.

Air Pollutants↗

PubMed1985

Development of a comparative potency method for cancer risk assessment of complex mixtures using short-term in vivo and in vitro bioassays.

A comparative potency method for cancer risk assessment has been developed based on a constant relative potency hypothesis. This method was developed and tested using data from a battery of short-term mutagenesis bioassays, animal tumorigenicity data and human lung cancer risk estimations. This data base was developed for a series of complex mixtures including emissions from coke ovens, roofing tar pots, cigarette smoke and automotive engines. The series of automobiles used in this study included both diesel- and gasoline-powered vehicles. The assumptions inherent in this method are discussed, together with the methods and data base used to test these assumptions.

Animals↗

PubMed2006

Gas-liquid chromatographic method for analysing complex mixtures of fatty acids including conjugated linoleic acids (cis9trans11 and trans10cis12 isomers) and long-chain (n-3 or n-6) polyunsaturated fatty acids. Application to the intramuscular fat of beef meat.

The optimisation and validation of a gas-liquid chromatographic (GLC) method using direct saponification with KOH/methanol followed by a derivatization with (trimethylsilyl)diazomethane was carried out trying to overcome all the difficulties posed by the analysis of complex mixtures of fatty acids (FAs) in animal fat tissues. The presented method allowed sensitive, selective and simultaneous determination of a wide range of different FAs, including short-chain FAs, branched-chain FAs and conjugated linoleic acid isomers in the same GLC run along with other well known saturated, monounsaturated and polyunsaturated FAs. To demonstrate the feasibility of the procedure, the total FA profile of beef meat was characterised.

Animals↗

PubMed1996

Potency of a complex mixture of polychlorinated dibenzo-p-dioxin, dibenzofuran, and biphenyl congeners compared to 2,3,7,8-tetrachlorodibenzo-p-dioxin in causing fish early life stage mortality.

Use of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) toxicity equivalents concentration (TEC) assumes that polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs), and biphenyls (PCBs) act additively and via a common mechanism to cause toxicity. To test these assumptions, 11 TCDD-like congeners and three non-TCDD-like congeners were combined at ratios typically found in Lake Michigan lake trout. The potency of the mixture, expressed as TEC based on fish-specific toxic equivalency factors, was compared to TCDD for producing lake trout and rainbow trout early life stage mortality. Signs of toxicity following exposure of newly fertilized eggs to the mixture or to TCDD were indistinguishable; sac fry mortality associated with blue-sac disease, and slopes of the dose-response curves for percentage sac fry mortality versus egg TEC or versus egg TCDD were parallel. However, the mixture dose-response curves were significantly shifted to the right of the TCDD dose-response curves by 1.3- and 1.8-fold as illustrated by LD50 values. Following exposure to the mixture or TCDD, LD50S for lake trout early life stage mortality were 97 (89-110) pg TE/g egg and 74 (70-80) pg TCDD/g (LD50, 95% fiducial limits) and for rainbow trout were 362 (312-406) pg TE/g egg and 200 (148-237) pg TCDD/g egg. These data suggest that TCDD-like congeners act via a common mechanism to cause toxicity during trout early development, but may not act strictly additively when combined in a mixture of TCDD- and non-TCDD-like congeners at ratios found in Great Lakes fish. The deviation from additivity, however, is less than current safety factors of 10-fold commonly applied in ecological risk assessments, providing support for the continued use of a TE additivity model for assessing risk posed by complex mixtures of PCDDs, PCDFs, and PCBs to fish.

Animals↗

PubMed2004

Evaluating exposures to complex mixtures of chemicals during a new production process in the plastics industry.

The goal of this study was to monitor emission of chemicals at a factory where plastics products were fabricated by a new robotic (impregnated tape winding) production process. Stationary and personal air measurements were taken to determine which chemicals were released and at what concentrations. Principal component analyses (PCA) and linear regression were used to determine the emission sources of different chemicals found in the air samples. We showed that complex mixtures of chemicals were released, but most concentrations were below Dutch exposure limits. Based on the results of the principal component analyses, the chemicals found were divided into three groups. The first group consisted of short chain aliphatic hydrocarbons (C2-C6). The second group included larger hydrocarbons (C9-C11) and some cyclic hydrocarbons. The third group contained all aromatic and two aliphatic hydrocarbons. Regression analyses showed that emission of the first group of chemicals was associated with cleaning activities and the use of epoxy resins. The second and third group showed strong association with the type of tape used in the new tape winding process. High levels of CO and HCN (above exposure limits) were measured on one occasion when a different brand of impregnated polypropylene sulphide tape was used in the tape winding process. Plans exist to drastically increase production with the new tape winding process. This will cause exposure levels to rise and therefore further control measures should be installed to reduce release of these chemicals.

Air Pollutants, Occupational↗

PubMed2000

Photometric method for the quantification of chlorophylls and their derivatives in complex mixtures: fitting with Gauss-peak spectra.

Accurate quantification of pigments in mixtures is essential in all cases in which separation of pigments by chromatography is impracticable for one reason or another. An example is the analysis of in vivo formation of heavy metal-substituted chlorophylls in heavy metal-stressed plants. We describe here a novel, accurate UV/VIS spectrophotometric method for the quantification of individual chlorophyll derivatives in complex mixtures, which has the potential for universal applicability for mixtures difficult to separate. The method is based on the description of each pigment spectrum by a series of Gaussian peaks. A sample spectrum is then fitted by a linear combination of these "Gauss-peak spectra" including an automatic correction of wavelength inaccuracy and baseline instability of the spectrometer as well as a correction of the widening of absorbance peaks in more concentrated pigment solutions. The automatic correction of peak shifts can also partially correct shifts caused by processes like allomerization. In this paper, we present the Gauss-peak spectra for Mg-chlorophyll a, b, c, pheophytin a, b, c, Cu-chlorophyll a, b, c, and Zn-chlorophyll a in acetone; Mg-chlorophyll a, b, pheophytin a, b, Cu-chlorophyll a, b, allomerized Cu-chlorophyll a, b, and Zn-chlorophyll a, b in cyclohexane; Mg-chlorophyll a, b, pheophytin a, b, and Cu-chlorophyll a, b in diethyl ether.

Chemistry Techniques, Analytical↗

PubMed1997

Improved detection of polycyclic aromatic compounds in complex mixtures by liquid chromatographic fractionation on poly(divinylbenzene) prior to gas chromatography-mass spectrometry. Application to the analysis of diesel particulates.

Polycyclic aromatic compounds (PACs) are preferentially retained over other compound classes during high-performance liquid chromatography (HPLC) on poly(divinylbenzene) (PDVB) columns with a dichloromethane mobile phase. PAC retention during HPLC with PDVB/CH2Cl2 is governed by a multi-mode mechanism that has been previously described. This enhanced retention of PACs makes PDVB columns useful for isolating a PAC fraction from highly complex mixtures such as the emissions from fossil-fuels combustion. The cleaned-up PAC fraction yields a simple chromatogram with easily identified and quantified peaks without significant compound loss or danger of contamination. We illustrate the use of this clean-up method for the isolation of the PAC fraction from a standard reference diesel particulate sample.

Chromatography, High Pressure Liquid↗

PubMed1990

Use of bacterial assay system for monitoring genotoxic complex mixtures in the occupational setting.

Workplace environmental genotoxicity assessments, which may be carried out either by laboratory analysis or using an in-situ assay system, are potentially useful for health hazard evaluations, for industrial hygiene and biological (genetic) monitoring. Whenever possible, genotoxicity assays should be performed in conjunction with industrial hygiene studies to assess the biological activity of workplace contaminants. Efforts should continue to be made to establish a simple and reliable in-situ assay system for the detection and monitoring of genotoxic complex mixtures in the occupational setting.

Animals↗

PubMed1997

Risk assessment of complex mixtures: some considerations on polycyclic aromatic hydrocarbons in urban areas.

The comparative examination of experimental and epidemiological data, together with risk evaluations concerning coke-oven, diesel, and gasoline motor emissions, as well as specific PAH fractions and single PAHs, indicates that, at least under risk additivity hypothesis, benzo(a)pyrene (B(a) may account for only a relatively small amount of the whole carcinogenic potential of PAH mixtures. This finding emerges from the comparison of risk evaluations of coke-oven and diesel emissions (based on epidemiological and/or experimental data) with risk evaluations of B(a)P as a single substance (based on carcinogenic bioassay data), as well as from the results of experimental studies evaluating the carcinogenic potency of motor exhaust condensates, of specific condensate fractions (particularly, the 4-7 ring PAH fraction), and of B(a)P. These data indicate that B(a)P might account for a percentage of the whole mixture carcinogenic response, at least in the hypothesis of an additive effect of PAHs. However, the overall carcinogenic response and risk still appear at least approximately related to the B(a)P concentration in the examined PAH mixtures. Finally, recent findings on PAH relative potencies (compared with B(a)P potency) indicate that several PAH present in mixtures commonly detected in occupational and in the general environment are characterized by a carcinogenic potency comparable with or even higher than that of B(a)P. This confirms the above hypothesis with respect to the significant, but minor role, of B(a)P. This relatively coherent picture appears to confirm that the reference to B(a)P as a complex mixture index may still represent a reasonable solution. However, the selection of a few other indicators from among the PAH whose relative concentrations and relative carcinogenic potencies are higher might improve the analysis.

Animals↗

PubMed2005

Mycobacterial lipid II is composed of a complex mixture of modified muramyl and peptide moieties linked to decaprenyl phosphate.

Structural analysis of compounds identified as lipid I and II from Mycobacterium smegmatis demonstrated that the lipid moiety is decaprenyl phosphate; thus, M. smegmatis is the first bacterium reported to utilize a prenyl phosphate other than undecaprenyl phosphate as the lipid carrier involved in peptidoglycan synthesis. In addition, mass spectrometry showed that the muropeptides from lipid I are predominantly N-acetylmuramyl-L-alanine-D-glutamate-meso-diaminopimelic acid-D-alanyl-D-alanine, whereas those isolated from lipid II form an unexpectedly complex mixture in which the muramyl residue and the pentapeptide are modified singly and in combination. The muramyl residue is present as N-acetylmuramic acid, N-glycolylmuramic acid, and muramic acid. The carboxylic functions of the peptide side-chains of lipid II showed three types of modification, with the dominant one being amidation. The preferred site for amidation is the free carboxyl group of the meso-diaminopimelic acid residue. Diamidated species were also observed. The carboxylic function of the terminal D-alanine of some molecules is methylated, as are all three carboxylic acid functions of other molecules. This study represents the first structural analysis of mycobacterial lipid I and II and the first report of extensive modifications of these molecules. The observation that lipid I was unmodified strongly suggests that the lipid II intermediates of M. smegmatis are substrates for a variety of enzymes that introduce modifications to the sugar and amino acid residues prior to the synthesis of peptidoglycan.

Cell Wall↗

PubMed1997

Combined effects of complex mixtures of potentially anti-carcinogenic compounds on antioxidant enzymes and carcinogen metabolizing enzymes in the rat.

The anti-carcinogenic activity of dietary fruit and vegetables observed in several epidemiological and experimental animal studies is likely to be an effect of the combined exposure to a large number of substances acting together. This is plausible, as these compounds are present simultaneously in a diet containing vegetables and fruit. Further, some compounds have been experimentally demonstrated to modify several mechanisms involved in carcinogenesis. The effect of combined exposure is demonstrated in the present article, summarizing the effects of a complex mixture of anti-carcinogenic substances (from broccoli) on different antioxidative defense enzymes and on cytochrome P-450 activities in rat liver, kidney and colon. The responses were related to the levels of different specific glucosinolates.

Animals↗

PubMed2003

Effect-directed analysis: a promising tool for the identification of organic toxicants in complex mixtures?

Wastewater effluents, groundwater, surface water, sediments, soils and air particulate matter are often contaminated by a multitude of chemicals. Since often no a priori knowledge of relevant toxicants exists, chemical analysis alone is not an appropriate tool for hazard assessment. Instead, a linkage of effect data and hazardous compounds is required. For that purpose, effect-directed analysis (EDA) was developed, which is based on a combination of biotesting, fractionation procedures and chemical analytical methods. Since a controversial discussion about the prospects of success in relation to the expense exists, the current methodological state of EDA for organic toxicants in complex mixtures and important results are reviewed in this paper with the aim of establishing criteria for the successful use of this promising tool. While EDA is a powerful tool to identify specifically acting individual toxicants close to the source of emission, it is inappropriate for screening purposes and often may fail in remote areas where the concentrations of specific toxicants are too low relative to the nonspecific toxicity of the whole mixture of natural and anthropogenic compounds. The biological tools have to be carefully selected with respect to their ability to detect specific effects and their significance in hazard assessment. Sophisticated chemical tools are required to identify individual toxicants in mixtures of thousands of compounds, which are typical for contaminated environments.

Air Pollutants↗

PubMed1977

Detection of amphiphilic proteins and peptides in complex mixtures. Charge-shift crossed immunoelectrophoresis and two-dimensional charge-shift electrophoresis.

Charge-shift electrophoresis has been suggested as a simple and novel method for differentiating between emphiphilic and hydrophilic proteins (Helenius, A. and Simons, K. (1977) Proc. Natl. Acad. Sci. U.S. 74, 529-532.) This communication reports on the combination of charge-shift electrophoresis with second dimensional quantitative immunoelectrophoresis, and on a two-dimensional modification of the charge-shift electrophoresis technique. From results obtained with unfractionated human plasma proteins and human erythrocyte membrane proteins we conclude that these modifications reliably permit detection of amphiphilic proteins and peptides in complex mixtures.

Blood Proteins↗