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A laboratory calibration study was undertaken with juvenile Sepia officinalis (80-85 g initial wet weight) to investigate the effects of different food rations and different starving intervals on RNA/dry weight (DW) ratios and RNA/DNA ratios in cephalopod mantle muscle at two different temperatures. The digestive gland index was also used as an additional indicator of recent growth. High food rations and low temperature went along with high RNA/DW ratios and high RNA/DNA ratios. Starving resulted in a linear decline in growth performance and a concomitant decrease in RNA/DW and RNA/DNA ratio, with RNA/DNA ratios representing the growth data better. RNA/DNA ratios decreased faster at higher temperatures. A fluorimetric assay for nucleic acid analysis was optimized for cephalopod mantle tissues and yielded reproducible RNA/DNA ratios with a relative variance below 10%. Thus, it may be possible to use this estimator of recently encountered feeding regime for the evaluation of mortality rates of early teuthid paralarvae to eventually support stock management. Also, log relative digestive gland weight showed a strong relationship with starving time, but, surprisingly, not with temperature. Data from the two temperatures analyzed could be combined to form a common regression line of relative digestive gland index with starving time. This indicator for recent growth might be especially suitable for large specimens with a well-developed digestive gland.  相似文献   
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Deglycosylation of ricin may be necessary to prevent the entrapment of antibody-ricin conjugates in vivo by cells of the reticuloendothelial system which have receptors that recognise the oligosaccharide side chains on the A- and B-chains of the toxin. Carbohydrate-deficient ricin was therefore prepared by recombining the A-chain, which had been treated with alpha-mannosidase, with the B-chain, which had been treated with endoglycosidase H or alpha-mannosidase or both. By recombining treated and untreated chains, a series of ricin preparations was made having different carbohydrate moieties. The removal of carbohydrate from the B-chain did not affect the ability of the toxin to agglutinate erythrocytes, and alpha-mannosidase treatment of the A-chain did not affect its ability to inactivate ribosomes. The toxicity of ricin to cells in culture was only reduced in those preparations containing B-chain that had been treated with alpha-mannosidase, when a 75% decrease in toxicity was observed. The toxicity of the combined ricin preparation to mice varied from double to half that of native ricin, depending on the chain(s) treated and the enzymes used. Removal of carbohydrate greatly reduced the hepatic clearance of the toxin and the levels of toxin in the blood were correspondingly higher. These results suggest that antibody-ricin conjugates prepared from deglycosylated ricin would be cleared more slowly by the liver, inflict less liver damage, and have greater opportunity to reach their target.  相似文献   
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Bordetella pertussis, the etiologic agent of whooping cough, produces a calmodulin-sensitive adenylate cyclase which elevates intracellular cAMP in a variety of eucaryotic cells. Exogenous calmodulin added to the partially purified adenylate cyclase has been shown to inhibit invasion of animal cells by this enzyme (Shattuck, R. L., and Storm, D. R. (1985) Biochemistry 24, 6323-6328). In this study, several properties of the calmodulin-sensitive adenylate cyclase are shown to be influenced by Ca2+ in the absence of calmodulin. The presence or absence of Ca2+ during QAE-Sephadex ion exchange chromatography produced two distinct chromatographic patterns of adenylate cyclase activity. Two different forms of the enzyme (Pk1 and Pk2EGTA) were isolated by this procedure. Pk1 adenylate cyclase readily elevated intracellular cAMP levels in mouse neuroblastoma cells (N1E-115) while Pk2EGTA adenylate cyclase had no effect on cAMP levels in these cells. Gel exclusion chromatography of Pk1 adenylate cyclase gave apparent Stokes radii (RS) of 43.5 A (+/- 1.3) in the presence of 2 mM CaCl2 and 33.8 A (+/- 0.94) in the presence of 2 mM EGTA [( ethylenebis (oxyethylenenitrilo)]tetraacetic acid). These Stokes radii are consistent with molecular weights of 104,000 (+/- 6,400) and 61,000 (+/- 3,600), respectively. Pk2EGTA adenylate cyclase had an apparent RS of 33.0 (+/- 1.2) (Mr = 60,600 (+/- 2,800] in the presence of Ca2+ or excess EGTA. At 60 degrees C, Pk1 adenylate cyclase exhibited a Ca2+-dependent heat stability with a half-life for loss of enzyme activity of 10.3 min in 5 mM CaCl2 and a half-life of 2.8 min in the presence of 0.1 microM CaCl2. The stability of Pk2EGTA adenylate cyclase was not affected by changes in free Ca2+. The adenylate cyclase preparations described above were submitted to sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis, and enzyme activity was recovered from gel slices by extraction with detergent containing buffers. The catalytic subunit isolated from SDS-polyacrylamide gels was activated 7-fold in the presence of Ca2+ with maximum activity observed at 1 microM free Ca2+. With both preparations, the apparent molecular weight of the catalytic subunit on SDS gels was 51,000 in the presence of 2 mM CaCl2 and 45,000 in the presence of 2 mM EGTA. The catalytic subunit of the enzyme was purified to apparent homogeneity by preparative SDS-polyacrylamide gel electrophoresis and resubmitted to SDS gel electrophoresis in the presence or absence of free Ca2+. The purified catalytic subunit also exhibited a Ca2+-dependent shift in its mobility on SDS gels.(ABSTRACT TRUNCATED AT 400 WORDS)  相似文献   
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Seasonal carbon isotope discrimination in a grassland community   总被引:11,自引:0,他引:11  
Summary Grassland communities of arid western North America are often characterized by a seasonal increase in ambient temperature and evaporative demand and a corresponding decline in soil moisture availability. As the environment changes, particular species could respond differently, which should be reflected in a number of physiological processes. Carbon isotope discrimination varies during photosynthetic activity as a function of both stomatal aperture and the biochemistry of the fixation process, and provides an integrated measure of plant response to seasonal changes in the environment. We measured the seasonal course of carbon isotope discrimination in 42 grassland species to evaluate changes in gas exchange processes in response to these varying environmental factors. The seasonal courses were then used to identify community-wide patterns associated with life form, with phenology and with differences between grasses and forbs. Significant differences were detected in the following comparisons: (1) Carbon isotope discrimination decreased throughout the growing season; (2) perennial species discriminated less than annual species; (3) grasses discriminated less than forbs; and (4) early flowering species discriminated more than the later flowering ones. These comparisons suggested that (1) species active only during the initial, less stressful months of the growing season used water less efficiently, and (2) that physiological responses increasing the ratio of carbon fixed to water lost were common in these grassland species, and were correlated with the increase in evaporative demand and the decrease in soil moisture.  相似文献   
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Multinuclear (1H and 31P) nuclear magnetic resonance (NMR) spectroscopy and quasi-elastic light scattering have been used to characterize molecular aggregates formed in dilute sodium taurocholate--egg lecithin solutions. When mixed micelles (1.25 g/dL) are diluted with 150 mM aqueous sodium chloride, light-scattering measurements suggest a transformation from mixed micelles to unilamellar vesicle species. Decreased 1H NMR line widths for bile salt resonances are consistent with predominance of a monomer form. The concurrent appearance of a second phospholipid choline methyl resonance indicates two types of phospholipid environment in slow chemical exchange: this behavior is consistent with small unilamellar vesicles. The appearance of bilayer vesicles in dilute model bile solutions is confirmed by addition of a lanthanide shift reagent (Pr3+), which splits the 1H or 31P head-group peak into two components with distinct chemical shift sensitivities. These mixed micelle and vesicle aggregates are also distinguished by their susceptibility to the lipolytic enzyme phospholipase A2 from cobra venom.  相似文献   
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A rapid, semiautomated cytophotometry system for quantitative histochemistry and cytochemistry was constructed. The system consists of a Fairchild charge coupled device (CCD) image camera, a Zeiss Universal microscope, a Datacube analog to digital converter, and a digital Equipment Corporation LSI 11/23 computer operating under RT-11. Computer programs were written in FORTRAN and the MACRO assembly language for the acquisition of data from the CCD device. These data were then used for image segmentation, image display, and calculation of total optical density, perimeter, cell area, and several shape features. The reproducibility of measurement made with the CCD-based cytophotometry system was tested by repeated measurements. The coefficient of variation was estimated to be 1.7% for total optical density and 0.9% for cell area. The CCD-based cytophotometry system was further evaluated by comparing results with measurements made on the same cells with a scanning stage cytophotometer using the HIDACSYS computer programs. Correlation coefficients of 0.96 for total optical density and 0.91 for cell area were obtained between the two systems. We conclude that the high-speed, dimensional stability, small size, and linearity of the CCD-based cytophotometry system will make it useful for quantitative histochemistry and cytochemistry.  相似文献   
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