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41.
MTBE is a colorless, relatively volatile liquid that has found widespread use as an octane‐enhancing gasoline additive. In 1987, the Environmental Protection Agency's (EPA) Interagency Testing Committee identified MTBE for priority testing consideration based on large production volume, potential widespread exposure, and limited data on chronic health effects. In response, the industry formed the MTBE Health Effects Testing Task Force, which in 1988 signed a Consent Agreement with the EPA requiring the task force member companies to perform toxicological testing on MTBE.

The testing program, which began in the second quarter of 1988, consists of a full complement of short‐ and long‐term tests. The testing completed to date includes genotoxicity (in vivo bone marrow cytogenetics and Drosophila sex‐linked recessive lethal assays), developmental toxicity, acute and subchronic neurotoxicity (motor activity, functional observation battery, and neuropathology), subchronic toxicity, reproductive/fertility effects, and pharmacokinetic studies. There is also an ongoing oncogenicity study in rats and mice. The final report for this chronic study is expected at the end of 1992. The total cost for the program is approximately $3.75 million, which is funded by the 11 Task Force member companies based on market share.

These studies were sponsored by the MTBE Health Effects Testing Task Force, Oxygenated Fuels Association, Washington, D.C.  相似文献   

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Thirty minutes of total cerebral ischemia (decapitation) decreased total glutathione (GSH + GSSG) by 7% but had no detectable effect on the concentration of oxidized glutathione (GSSG), reduced ascorbate, or total ascorbate. In a model of reversible, bilateral hemispheric ischemia (four-vessel occlusion) no changes in glutathione or ascorbate were detected after 30 min of ischemia. During 24 h of reperfusion following such an insult no detectable change in total ascorbate, reduced ascorbate, or oxidized glutathione was noted; however, total brain glutathione declined by 25%. The findings are discussed in relation to the hypothesis that the deleterious effects of ischemia are due to an increase in free radical production which in turn leads to increased lipid peroxidation.  相似文献   
45.
Chromosomal DNA fiber autoradiography was used to examine the replicon properties of root-tip meristem cells of Helianthus annuus intact seedlings grown at temperatures from 10 to 38° C and those of root-tip cells grown in vitro at 23°. The average replicon size was approximately 22 m and it did not change with temperature nor when the roots were grown in culture. The average fork rate was 6 m/h at 10° and it rose gradually to 12 m/h at 38°. The responses of replication fork movement and of the duration of S to temperature were of three types: those in which change in fork rate was primarily (more than 90%) responsible for change in the duration of S, those in which the fork rate remained constant while S increased nearly twofold, and those in which the duration of S increased even though the replication forks were moving faster. The first type of response listed was observed at temperatures from 20 to 35°, the second type listed was observed at 10 to 15°, and the third, was produced at 38°.  相似文献   
46.
The yellow-cheeked vole (Microtus xanthognathus) shows two electrophoretic hemoglobin components. Electrophoresis of the polypeptide chains from the separated hemoglobin components shows identical β-chains but two α-chains of different mobility, α f and α s . The composition of soluble tryptic peptides was determined for each α-chain. Amino acid differences were found in peptides αT1 and αT9; the compositions of the remainder of the homologous peptides were identical. Differences in αT1, found at α4 (α s -Gly-α f -Val) and α5 (α s -Thr-α f -Asp), were confirmed after a run to residue 20 of the fast component in an automatic sequencer. The differences in charge between αT1 peptides can account for the electrophoretic pattern of two hemoglobins. This is the first time that it has been possible to identity the residues which can account for the charge difference between the two hemoglobins observed in a Microtus species.  相似文献   
47.
We have previously reported that lymphocytes from W/Fu rats immunized with syngeneic (C58NT)D tumor cells were cytotoxic against these cells in a 4-hr 51Cr release assay. We have investigated the feasibility of cryopreserving lymphocytes and target cells and have selected freezing conditions which provide good yields of viable cells and functional activity. Lymphocytes from different animals had a recovery of 60–80% viability which resulted in a corresponding 55–75% recovery of cytotoxic activity. Repeated testing of lymphocyte cytotoxicity from a pool of frozen spleen cells against either fresh or frozen (C58NT)D cells gave reproducible cytotoxicity. In addition, recovery of high levels of lymphocyte function was also demonstrated when cryopreserved cells were employed in long-term cytotoxic assays, i.e., 3H-proline and 125IUdR release assays, in the lymphoproliferative response to mitogens (PHA and Con A)3 or tumor cells (MLTI) as measured by 3H-thymidine incorporation, and in the in vitro generation of secondary cytotoxicity.By employing these cryoprotective techniques it is possible to have: 1) a population of lymphoid cells with known functional activity and 2) a pool of target cells with known susceptibility to lysis and antigenic content. Furthermore, the use of frozen cells as internal standards in each test also permits the analysis of assay variation as well as the study of variation in various cell types.  相似文献   
48.
The predominant sulfated polysaccharide, ?-carrageenan, was localized in the middle lamella of epidermal, cortical and medullary cells of Eucheumanudum J. Agardh. Autoradiographic studies with 35SO4= indicated that the label was first incorporated in the inner wall and ultimately deposited in the middle lamella of all cells, and in an outer wall layer of the epidermal cells. There was no evidence for cytoplasmic incorporation of the label. The middle lamella stained with alcian blue, was γ-metachromatic with toluidina blue O and bound diaminobenzidine-osmium tetroxide. This region was also positive with periodic acid-Schiff's (PAS) ragent, possibly demonstrating cellulose and/or a nonsulfated precursor of ?-carrageenan. A proposed model for extracellular sulfation includes production and secretion of a nonsulfated polygalactan and sulfotransferase enzyme(s) by the golgi apparatus and endoplasmic reticulum, respectively. Free sulfate in the wall would be bound to the precursor polysaccharide, with much of the resulting carrageenan migrating to the middle lamella facilitating mutual cell growth.  相似文献   
49.
The ultrastructure of chloroplasts from 28 of the 73 species of Caulerpa Lamouroux (Chlorophyta, Caulerpales) has been studied to aid in interpreting phylogenetic relationships among the 12 recognized sections. Variations of systematic value include pyrenoid occurrence and fine structure, thylakoid architecture and amount of photosynthate storage. Comparisons of field and culture specimens indicate these characters are consistent. Chloroplast thylakoids are grouped into bands, with the distribution of bands differing among species. In the most common arrangement, bands are evenly distributed throughout the chloroplast. A few species show lateral displacement of bands whereas others have a majority of bands arranged at one end of the chloroplast. Starch is stored cither as one or two large grains (> 1 μm diam.) or numerous small grains (< 0.5 μm diam.). Electron-transparent regions are common in other species in which chloroplasts rarely store starch. Simple, embedded pyrenoids are present in several species of section Sedoideae. An opaque region occurs in chloroplasts of C. elongata which may represent an intermediate stage in the evolutionary loss of the pyrenoid. It is suggested that the chloroplast of Caulerpa evolved, from a large, complex, pyrenoid-containing organelle housing both photosynthetic and amylogenic functions, to a small, structurally simpler one, specialized for photosynthesis alone. A phylogeny of the 12 sections of Caulerpa is constructed, based on chloroplast evolution which agrees with an earlier morphology-based hypothesis on the origin and evolution of Caulerpa.  相似文献   
50.
The inhibitory effect of a series of analogs of CPTA, 2-(4-chlorophenylthio)-triethylamine-HCl, and ammonia derivatives on carotenoid biosynthesis in Phycomyces blakesleeanus mutants was studied. The types of inhibition exhibited allowed no firm conclusions about the biosynthetic route to β-carotene from either β-zeacarotene or lycopene. However, the evidence suggests at present that both pathways are operative. It was found that a slight change in structure of inhibitor resulted in a different type of action. Conclusions based on a single inhibitor could be cited as “evidence” for a certain pathway.  相似文献   
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