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PubMed2001

Rhizobium sp. BR816 produces a complex mixture of known and novel lipochitooligosaccharide molecules.

Rhizobial lipochitooligosaccharide (LCO) signal molecules induce various plant responses, leading to nodule development. We report here the LCO structures of the broadhost range strain Rhizobium sp. BR816. The LCOs produced are all pentamers, carrying common C18:1 or C18:0 fatty acyl chains, N-methylated and C-6 carbamoylated on the nonreducing terminal N-acetylglucosamine and sulfated on the reducing/terminal residue. A second acetyl group can be present on the penultimate N-acetylglucosamine from the nonreducing terminus. Two novel characteristics were observed: the reducing/terminal residue can be a glucosaminitol (open structure) and the degree of acetylation of this glucosaminitol or of the reducing residue can vary.

Carbohydrate Conformation↗
PubMed1995

The bark of Robinia pseudoacacia contains a complex mixture of lectins. Characterization of the proteins and the cDNA clones.

Two lectins were isolated from the inner bark of Robinia pseudoacacia (black locust). The first (and major) lectin (called RPbAI) is composed of five isolectins that originate from the association of 31.5- and 29-kD polypeptides into tetramers. In contrast, the second (minor) lectin (called RPbAII) is a hometetramer composed of 26-kD subunits. The cDNA clones encoding the polypeptides of RPbAI and RPbAII were isolated and their sequences determined. Apparently all three polypeptides are translated from mRNAs of approximately 1.2 kb. Alignment of the deduced amino acid sequences of the different clones indicates that the 31.5- and 29-kD RPbAI polypeptides show approximately 80% sequence identity and are homologous to the previously reported legume seed lectins, whereas the 26-kD RPbAII polypeptide shows only 33% sequence identity to the previously described legume lectins. Modeling the 31.5-kD subunit of RPbAI predicts that its three-dimensional structure is strongly related to the three-dimensional models that have been determined thus far for a few legume lectins. Southern blot analysis of genomic DNA isolated from Robinia has revealed that the Robinia bark lectins are the result of the expression of a small family of lectin genes.

Amino Acid Sequence↗
PubMed2000

Fractional simplex designs for interaction screening in complex mixtures.

In mixture experiments, one may be interested in estimating not only main effects but also some interactions. Main effects and significant interactions in a mixture may be estimated through appropriate mixture experiments, such as simplex-centroid designs. However, for mixtures with a large number of factors, the run size for these designs becomes impractically large. A subset of a full simplex-centroid design may be used, but the problem remains regarding which factor-level settings should be selected. In this paper, we propose a solution that considers design points with either one or p individual nonzero factor-level settings. These fractional simplex designs provide a means of screening for interactions and of investigating the behavior of many-component mixtures as a whole while greatly reducing the run size compared with full simplex-centroid designs. The means of construction of the design arrays is described, and designs for < or = 31 factors are presented. Some of the proposed methodology is illustrated using generated data.

Algorithms↗
PubMed1975

Absorption of amino acids and peptides from a complex mixture in the isolated small intestine of the rat.

Amino acid and peptide absorption from a pancreatic digest of casein at low concentration by an isolated preparation of perfused rat small intestine has been measured. 2. The rate of absorption of each amino acid (free or peptide-bound) is closely proportional to its concentration in the perfusate; this implies a constant Vmax/Km ration for all amino acids in the mixture. 3. There is a high correlation between the compositions of luminal perfusate and secretion into the tissue fluid (apart from the content of glutamic and aspartic acids and alanine). 4. The concentrations of each free amino acid are, on average, 9 times as great in secretion as in lumen; the total peptide-N concentration in secretion is approximately 4 times that in the lumen. 5. The rate of absorption of each free amino acid is highly negatively dependent on the rate of absorption of that amino acid in peptide-bound form, in addition to being positively dependent on the perfusate concentration of free amino acid. 6. While peptide-bound proline appears to be well absorbed, free proline liberated by hydrolysis appears to pass back into the lumen as well as into the tissue fluid. Substantial back flux of hydrolysis products may occur for all amino acids. 7. About one-third of the amino acids appearing in the secretion on the serosal surface are peptide-bound. 8. The rate of absorption of peptides appears to determine the rate of their hydrolysis which probably occurs mainly after entry into the mucosal cells.

Amino Acids↗
PubMed1994

Nonrepresentative PCR amplification of variable gene sequences in clinical specimens containing dilute, complex mixtures of microorganisms.

PCR amplification and DNA sequencing of the expression locus from Neisseria gonorrhoeae contained in urine sediments collected from experimentally infected human subjects produced two observations. First, different pilin sequences were obtained when separate aliquots of the same sample were amplified and sequenced. In contrast, the same pilin sequence was obtained when repeated amplifications were performed on individual colonies grown from the clinical samples. Second, mixed sequences (i.e., more than one nucleotide at variable positions in the pilin gene sequence) were observed in both the direct clinical isolates and individual cultures grown from the isolates. These results suggest that when clinical samples are directly examined by PCR amplification and sequencing, multiple amplifications may be required to detect sequence variants in the sample and minority variant sequences will not always be detected.

Adolescent↗
PubMed1983

General approach to the biological analysis of complex mixtures.

The study of potential health effects of combustion effluents involves identifying the substances present and estimating the probable health hazards of each. Unfortunately, this second step cannot be done by using present techniques. Approximations of health hazards by bacterial and human cell assays are being used to set priorities for further biological studies and to suggest needs for modifications of combustion systems. The assumptions underlying this approximation are discussed, and several examples of combustion effluents are reviewed.

Air Pollutants↗
PubMed1991

Populations at risk: addressing health effects due to complex mixtures with a focus on respiratory effects.

Some individuals in the population may be sensitive or susceptible be to the effects of air pollutants. Such sensitivity may be to specific pollutants or classes of pollutants. However, sensitivity or susceptibility in some individuals can be to all irritants, but the sensitivity is likely to be response specific or organ specific. The U.S. Clean Air Act specifically recognizes that some individuals in the population are sensitive to air pollutants and indicates that such individuals need to be protected by air quality standards. It is usually difficult to determine the cause of sensitivity, though various biological mechanisms have been studied. Biological age may be a factor, with the young being most sensitive and susceptible to being affected. An example is the heightened bronchial lability and responsiveness in the very young that appears to disappear with growth. Susceptibility may be innate (e.g., genetic) and/or induced by events/exposures. Frequently, those with preexisting illnesses are part of the sensitive population because they may often respond, sometimes hyperrespond, to a pollutant exposure that may not affect most people. Asthmatics are excellent examples of individuals who were susceptible to the disease and, once inflicted, are susceptible to the effects of many environmental and nonenvironmental agents. Usually only a fraction of the general population will respond with heightened reactions at lower doses. Such individuals require special evaluation and attention in all exposure-response studies and risk assessments. Thus, the conditions defining populations at risk and the methodologies to discover and study them can be reviewed.

Air Pollutants↗
PubMed1991

Methods to assess respiratory effects of complex mixtures.

This paper evaluates the influence of exposures on acute and chronic airway obstruction. Clinical, physiological, and immunological aspects are important in evaluating the effects of the pollutant exposures. Aspects of the exposure-response relationships important enough to record are those factors interactive with the pollutants (e.g., smoking and other personal/behavioral factors) and precursor conditions. To determine baseline status and study chronic effects, one uses standardized and modified health questionnaires and standardized pulmonary function. Confirmatory studies of responsive airways, potentially assessed first by diurnal peak flow, can be done using post-bronchodilator maximum expiratory flow volume curves and methacholine challenges. Immunoglobulin determinations for immunological status (a predisposing/susceptibility factor), allergy skin tests (for immediate hypersensitivity status), and blood counts (mostly for eosinophils) are also important. Other tests that could be performed include expired carbon monoxide and/or carboxyhemoglobin and methemoglobin (for smoking and combustion exposures). Measures of acute effects are symptomatic responses (by questionnaires and diaries), responses of the airways (as measured by spirometry and peak flows), and changes in medication usage or associated medical care (in diaries). Methodologies should also include discussions of protocols and analysis.

Air Pollutants↗
PubMed1993

Toxicological approaches to complex mixtures.

This paper reviews the role of toxicological studies in understanding the health effects of environmental exposures to mixtures. The approach taken is to review mixtures that have received the greatest emphasis from toxicology; major mixtures research programs; the toxicologist's view of mixtures and approaches to their study; and the complementary roles of toxicological, clinical, and epidemiological studies. Studies of tobacco smoke, engine exhaust, combustion products, and air pollutants comprise most of the past research on mixtures. Because of their great experimental control over subjects, exposures, and endpoints, toxicologists tend to consider a wider range of toxic interactions among mixture components and sequential exposures than is practical for human studies. The three fundamental experimental approaches used by toxicologists are integrative (studying the mixture as a whole), dissective (dissecting a mixture to determine causative constituents), and synthetic (studying interactions between agents in simple combinations). Toxicology provides information on potential hazards, mechanisms by which mixture constituents interact to cause effects, and exposure dose-effect relationships; but extrapolation from laboratory data to quantitative human health risks is problematic. Toxicological, clinical, and epidemiological approaches are complementary but are seldom coordinated. Fostering synergistic interactions among the disciplines in studying the risks from mixtures could be advantageous.

Air Pollutants↗
PubMed1993

Complex mixtures and indoor air pollution: overview of epidemiologic methods.

The likelihood of an epidemiologic study correctly identifying an adverse health outcome associated with exposure to indoor air pollutants is increased if a) substantial variation exists in the frequency or level of exposure among study subjects otherwise at similar risk of the health outcome; b) the number of study subjects or study communities is large; c) the health outcome can be assessed with accuracy; d) relevant exposure levels can be measured with accuracy; e) an unbiased sample of exposed and nonexposed subjects is selected for study; and f) other determinants of the adverse health outcome can be measured. Nonetheless, given a strong enough impact of exposure to one pollutant or a mixture of pollutants on the risk of illness, it is possible for epidemiologic studies to discern a relation even if only some of the above circumstances are present.

Air Pollution, Indoor↗
PubMed1998

Environmental complex mixture toxicity assessment.

Trichloroethylene (TCE) was found as a contaminant in the well supplying water to an aquatic testing laboratory. The groundwater was routinely screened by a commercial laboratory for volatile and semivolatile compounds, metals, herbicides, pesticides, and polychlorinated biphenyls using U.S. Environmental Protection Agency methods. Although TCE was the only reportable peak on the gas chromatograph, with average concentrations of 0.200 mg/l, other small peaks were also present, indicating the possibility that the contamination was not limited to TCE alone. A chronic 6-month carcinogenicity assay was conducted on-site in a biomonitoring trailer, using the Japanese medaka fish (Oryzias latipes) in an initiation-promotion protocol, with diethylnitrosamine (DEN) as the initiator and the TCE-contaminated groundwater as a promoter. Study results indicated no evidence of carcinogenic potential of the groundwater without initiation. There was, however, a tumor-promotional effect of the groundwater after DEN initiation. A follow-up laboratory study was conducted using reagent grade TCE added to carbon-filtered groundwater to simulate TCE concentrations comparable to those found in the contaminated groundwater. Study results indicated no promotional effects of TCE. These studies emphasize the necessity for on-site bioassays to assess potential environmental hazards. In this instance, chemical analysis of the groundwater identified TCE as the only reportable contaminant, but other compounds present below reportable limits were noted and may have had a synergistic effect on tumor promotion observed with the groundwater exposure. Laboratory toxicity testing of single compounds can produce toxicity data specific to that compound for that species but cannot take into account the possible toxic effects of mixtures of compounds.

Adenoma, Liver Cell↗