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51.
Peterson PA 《Genetics》1966,54(1):249-266
52.
Richard P. Bunge Mary Bartlett Bunge Edith R. Peterson 《The Journal of cell biology》1965,24(2):163-191
53.
Plasma concentrations of pituitary hormones in 2,3,7,8-tetrachlorodibenzo-p-dioxin-treated male rats 总被引:1,自引:0,他引:1
R W Moore J A Parsons R C Bookstaff R E Peterson 《Journal of biochemical toxicology》1989,4(3):165-172
Experiments were conducted to test the hypothesis that acute TCDD toxicity is associated with pituitary hypofunction. Sexually mature male Sprague-Dawley rats were given graded doses of TCDD (0-100 micrograms/kg) and evaluated 7 days later. Despite pronounced hypophagia and body weight loss, plasma concentrations of growth hormone (GH), follicle-stimulating hormone (FSH), and luteinizing hormone (LH) were not significantly affected by any dose of TCDD. Only prolactin (PRL) concentrations were reduced, while, as previously reported, thyroid-stimulating hormone concentrations were elevated. Also, plasma LH, PRL, and adrenocorticotropic hormone (ACTH) concentrations were not significantly affected 1, 2, 3, 4, 5, or 7 days after a single dose of TCDD (50 micrograms/kg). We conclude that (1) pituitary hypofunction is not a major cause of the initial stages of acute TCDD toxicity, (2) growth retardation in TCDD-treated rats is not the result of a deficiency of GH, (3) alterations in plasma corticosterone concentrations are due to altered responsiveness of the adrenal to ACTH stimulation rather than to changes in plasma ACTH concentrations, and (4) that impaired spermatogenesis is not associated with a decrease in plasma FSH concentrations. In addition, the lack of a consistent effect on plasma PRL concentrations suggests that alterations in plasma PRL concentrations do not play a critical role in the toxicity of TCDD. Finally, because TCDD treatment causes a serious androgenic deficiency without increasing the rates at which androgens are catabolized or excreted, the fact that plasma LH concentrations were unaffected indicates that TCDD treatment must reduce the responsiveness of the testis to LH stimulation.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
54.
The role of litter in an old-field community: impact of litter quantity in different seasons on plant species richness and abundance 总被引:10,自引:0,他引:10
Summary We studied the effect of removing and adding plant litter in different seasons on biomass, density, and species richness in a Solidago dominated old-field community in New Jersey, USA. We removed all the naturally accumulated plant litter in November (658 g/m2) and in May (856 g/m2) and doubled the amount of litter in November and May in replicated plots (1 m2). An equal number of plots were left as controls. Litter removal and addition had little impact on total plant biomass or individual species biomass in the growing season following the manipulations. Litter removal, however, significantly increased plant densities but this varied depending upon the season of litter removal, species, and life history type. Specifically, the fall litter removal had a much greater impact than the spring litter removal suggesting that litter has its greatest impact after plant senescence in the fall and prior to major periods of early plant growth in spring. Annual species showed the greatest response, especially early in the growing season. Both spring and fall litter removal significantly increased species richness throughout the study. Litter additions in both spring and fall reduced both plant densities and species richness in June, but these differences disappeared near the end of the growing season in September. We concluded than in productive communities where litter accumulation may be substantial, litter may promote low species richness and plant density. This explanation does not invoke resource competition for the decline in species richness. Finally, we hypothesize that there may be broad thresholds of litter accumulation in different community types that may act to either increase or decrease plant yield and diversity. 相似文献
55.
D M Gawlowski B A Benjamin T V Peterson N R Harding H J Granger 《Proceedings of the Society for Experimental Biology and Medicine. Society for Experimental Biology and Medicine (New York, N.Y.)》1990,194(2):131-135
Natriuretic peptides elaborated by atrial myocytes promote marked renal sodium and water excretion as a mechanism for fluid and electrolyte balance. Recent evidence suggests that atriopeptin (ANP) also targets the non-renal vasculature as a site for enhanced fluid exchange. It remains unclear whether ANP alters microvascular integrity to facilitate the efflux of both plasma and proteins across the endothelial barrier, or if fluid exchange is selectively enhanced. This study evaluated the influence of ANP on macromolecular transport through the direct observation of microvessels in the hamster cheek pouch using fluorescent intravital microscopy. Fluorescein isothiocyanate conjugated to either bovine serum albumin or dextran 150,000 Mw was utilized as a permeability probe. Macromolecular efflux was quantified as fluorochrome clearance. The clearance of fluorescein-conjugated bovine serum albumin (57.94 +/- 7.03) or fluorescein-conjugated dextran 150 (4.09 +/- 1.35) remained unaltered by intravascular injection of 1 microgram/kg ANP. Topical application of 40 ng to cheek pouch microvessels produced similar results. All pouches demonstrated positive leakage response to histamine 2.5 x 10(-6) M, increasing fluorochrome clearance approximately 2- to 11-fold. Bolus injection of 1 microgram/kg ANP reduced mean arterial pressure, increased urine flow from 6.63 +/- 2.59 microliters/min to 8.20 +/- 6.13 microliters/min, and elevated sodium excretion from 1.37 +/- 0.49 microEq/min to 2.54 +/- 0.99 microEq/min. These results suggest that ANP fails to significantly alter the integrity of the protein-transporting channels in the microvascular exchange barrier. 相似文献
56.
Since crystallographic studies on Escherichia coli aspartate transcarbamoylase (ATCase) indicate that Gln 231 is in the active site of the enzyme and participates in the binding of the substrate, aspartate, it seemed of interest to examine mutant enzymes in which Gln 231 was replaced by Asn or Ile. The two mutant forms containing amino acid substitutions were characterized by a combination of steady-state kinetics, hydrodynamic measurements, and equilibrium ligand binding techniques. Both mutant forms exhibited a dramatic reduction in the affinity of the protein for substrates and substrate analogues as well as a very large decrease in catalytic activity. Moreover, the amino acid substitutions introduced within the active site of the enzyme led to unusual allosteric properties in the mutant enzymes. Although the bisubstrate analogue N-(phosphonoacetyl)-L-aspartate promotes the characteristic global conformational change in the mutant forms that is observed with the wild-type enzyme, the combination of substrate and substrate analogue does not. Cooperativity with respect to substrate binding is largely reduced compared to wild-type ATCase. Also, the effector molecules ATP and CTP which bind to the regulatory chains have dramatic effects on the activity of the mutant enzymes containing replacements for Gln 231 in the catalytic chains. In stark contrast to the wild-type enzyme, in which effects of nucleotides are manifested primarily by changes in the K0.5 of the enzyme, ATP and CTP have large effects on the Vmax of the mutant enzymes.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
57.
We examined the lymphatic concentration of 99mTc-albumin deposited in the air spaces of anesthetized sheep to determine whether changes in the concentration reflected changes in lung epithelial function. Five control sheep were ventilated with an aerosol of 99mTc-albumin for 6 min, and the lung lymphatic concentration of the tracer was monitored for the next 2 h. During the last 45 min the lymphatic concentration stabilized at a value that was 0.03 +/- 0.01% of the estimated value in the air spaces. Pulmonary vascular hypertension, induced in seven sheep by increasing the left atrial pressure 20 cmH2O for 4 h, increased the lung lymph flow from a base-line value of 3 +/- 2 to 21 +/- 14 ml/h. This caused the concentration of the 99mTc-albumin in the lymph to double to 0.07 +/- 0.03% of the air space concentration (P less than 0.01). Lung injury induced by infusing 0.08-0.10 ml/kg oleic acid intravenously in seven other sheep increased the lymphatic concentration of the 99mTc-albumin 10-fold to 0.31 +/- 0.09% of the air space concentration (P less than 0.01). The increased tracer concentration in the sheep with pulmonary vascular hypertension could be the result of the increased lymph flow causing a diversion of tracer into the lymphatics. However, a mathematical model showed that the 10-fold increase in the lymphatic concentration in the sheep with lung injury was primarily the result of an increase in both permeability and surface area of the epithelium that participated in the transfer of the 99mTc-albumin from the air spaces into the lung tissue drained by the lymphatics.(ABSTRACT TRUNCATED AT 250 WORDS) 相似文献
58.
Microbial Utilization of Estuarine Dissolved Organic Carbon: a Stable Isotope Tracer Approach Tested by Mass Balance 总被引:2,自引:0,他引:2 下载免费PDF全文
The natural stable isotope values of different plants have been used to trace the fate of organic carbon that enters estuarine ecosystems. Experiments were designed to determine the magnitude of (delta) (sup13)C changes of dissolved organic carbon (DOC) derived from tidal marsh vegetation that occurred during bacterial decomposition. Bacteria were grown on DOC leached from estuarine Spartina alterniflora and Typhus angustifolia plants. In four experiments, 25 to 80% of the initial carbon (2.6 to 9.1 mM organic C) was converted to bacterial biomass and CO(inf2). Mass balance calculations showed good recovery of total C and (sup13)C at the end of these experiments (100% (plusmn) 14% total C; (plusmn) 1(permil) (delta) (sup13)C). The (delta) (sup13)C values of DOC, bacterial biomass, and respired CO(inf2) changed only slightly in the four experiments by average values of -0.6, +1.4, and +0.5(permil), respectively. These changes are small relative to the range of (delta) (sup13)C values represented by different organic carbon sources to estuaries. Thus, microbial (delta) (sup13)C values determined in the field helped to identify the source of the carbon assimilated by bacteria. 相似文献
59.
The degradation of cytoplasmic antigens to peptides presented by class I MHC molecules is thought to be mediated by the ubiquitin/proteasome pathway. Support for this view came from our observation that the subunit composition of proteasomes can be changed by interferon-gamma (IFN-gamma) treatment. Thereby two subunits, LMP2 and LMP7, which are encoded in the MHC class II region, are incorporated into the proteasomal complex, whereas other subunits disappear. In the experiments reported in this communication we studied the subunit changes occurring in cell lines where the expression of LMP2 or LMP7 can be regulated individually either by IFN-gamma induction or by applying a new system to control the expression of transfected LMPs. In both situations LMP2 induction leads exclusively to the disappearance of housekeeping subunit 2, whereas LMP7 affects only subunit 10. Subunit 2 was found to be 76% homologous to LMP2. Since incorporation of LMP2 into the proteasomal complex prevents processing of the subunit 2 precursor, we conclude that LMP2 displaces subunit 2 during assembly. Subunit displacement is most likely a general mechanism to modulate the catalytic activity of the proteasomal complex without changing its structure. Furthermore, the controlled incorporation of transfected subunits into the complex offers a new approach to study proteasome function in vivo. 相似文献
60.
Melvin R. Duvall Paul M. Peterson Alan H. Christensen 《American journal of botany》1994,81(5):622-629
Restriction sites for six enzymes were mapped for the plastid DNAs of 25 species of Eragrostideae, one species of Cynodonteae (Eustachys distichophylla), and one species of Pooideae. Of the 124 restriction sites observed, 67 were variably present and shared by two or more species. These data were analyzed by the parsimony method using equal and unequal weights and by bootstrap analysis. The cladistic analyses established that members of the Muhlenbergiinae, including the genera Muhlenbergia, Blepharoneuron, Bealia, Chaboissaea, Lycurus, and Pereilema, share seven restriction site mutations and are strongly supported by the data as a monophyletic subtribe. Surprisingly, Redfieldia flexuosa also clustered with the Muhlenbergiinae in the analysis, perhaps indicative of a past interspecific hybridization event. The restriction sites data also weakly support a relationship (six shared mutations) between Erioneuron, Munroa, and Dasyochloa. 相似文献