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81.
Cartilage proteoglycan aggregates. Electronmicroscopic studies of native and fragmented molecules
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1. Proteoglycan aggregates from bovine nasal cartilage were studied by using electron microscopy of proteoglycan/cytochrome c monolayers. 2. The aggregates contained a variably long central filament of hyaluronic acid with an average length of 1037nm. The proteoglycan monomers attached to the hyaluronic acid appeared as side chain filaments varying in length (averaging 249nm). They were distributed along the central filament at an average distance of about 36nm. 3. Chondroitin sulphate side chains were removed from the proteoglycan monomers of the aggregates by partial chondroitinase digestion. The molecules obtained had the same general appearance as intact aggregates. 4. Proteoglycan aggregates were treated with trypsin and the largest fragment, which contains the hyaluronic acid, link protein and hyaluronic acid-binding region, was recovered and studied with electron microscopy. Filaments that lacked the side chain extensions and had the same length as the central filament in the intact aggregate were observed. 5. Hyaluronic acid isolated after papain digestion of cartilage extracts gave filaments with similar length and size distribution as observed for the central filament both in the intact aggregate and in the trypsin digests. 6. Umbilical-cord hyaluronic acid was also studied and gave electron micrographs similar to those described for hyaluronic acid from cartilage. However, the length of the filament was somewhat shorter. 7. The electron micrographs of both intact and selectively degraded proteoglycans corroborate the current model of cartilage proteoglycan structure. 相似文献
82.
The activities of NADPH and NADH oxidase were determined in homogenates of isolated pure parenchymal and nonparenchymal rat liver cells at neutral (7.4) and acid (5.5) pH. The NADPH oxidase at pH 7.4 is about equally active in parenchymal and nonparenchymal cells and in both cell types is rather insensitive to KCN (1 mm) inhibition. By lowering the pH to 5.5, the NADPH oxidase of the nonparenchymal cells is stimulated (twofold) while the activity in parenchymal cells is decreased. The NADH consumption at neutral pH in parenchymal cells is 75% inhibited by KCN, while this activity in nonparenchymal cells is relatively insensitive to KCN. The NADH oxidase in both parenchymal and nonparenchymal liver cells is less active when the pH is lowered from 7.4 to 5.5. The distribution of NAD(P)H oxidases between parenchymal and nonparenchymal liver cells and the effect of pH on their activities suggest that in the nonparenchymal cells, the NADPH oxidase might play a role in the synthesis of H2O2 within the phagocytic vacuole. A scheme is proposed which describes the metabolic events involved in H2O2 formation and catabolism of endo(phago)cytosed particles in nonparenchymal liver cells. 相似文献
83.
84.
Sixteen growing pigs were fed a vitamin E and selenium deficient diet; half of the animals (Group 2) were given a daily supply of vitamin E and selenium. After having been fed these diets for 53 days, the pigs were infected orally with minced colonic material from cases with typical swine dysentery. This exposure resulted in outbreaks of swine dysentery in both groups. The incubation times were, however, distinctly shorter and the clinical symptoms much more pronounced in Group 1 than in Group 2. The patho^morphological lesions in the colon also differed between the 2 groups. In the pigs of Group 1 evident pseudomembraneous lesions were observed in the spiral colon. In Group 2, the colonic alterations consisted predominantly of a catarrhal enteritis; pseudomembranes occurred in a minor part of colon in only 4 pigs. Both the clinical and the chemical observations and the pathological findings indicated a much better vitamin E and selenium balance in the pigs of Group 2. It is concluded that the treatment with vitamin E and selenium in Group 2 greatly increased resistance to swine dysentery. 相似文献
85.
86.
Johan B. Ubbink W. J. Hayward Vermaak Siegbert Bissbort 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》1991,565(1-2)
A rapid, isocratic high-performance liquid chromatographic (HPLC) method is described for the determination of total homocysteine levels in human serum. Prior to reversed-phase HPLC analysis, the serum thiols were derivatized with SBD-F (ammonium 7-fluorobenzo-2-oxa-1,3-diazole-4-sulphonate), a thiol-specific fluorogenic probe which is commercially available. Retention of SBD-homocysteine was sensitive to pH, and a mobile phase pH of 2.1 ensured baseline separation of serum thiols within 6 min. The method is simple, sensitive, reproducible (between-run coefficient of variation of 6.6%) and very suitable for routine determination of serum homocysteine levels in a clinical pathology laboratory. 相似文献
87.
Johan C. Sanders M. Francesca Ottaviani Arie van Hoek Antonie J. W. G. Visser Marcus A. Hemminga 《European biophysics journal : EBJ》1992,21(5):305-311
Model membranes with unsaturated lipid chains containing various amounts of M13 coat protein in the -helical form were studied using time-resolved fluorescence and ESR spectroscopy. The lipid-to-protein (L/P) ratios used were > 12 to avoid protein-protein contacts and irreversible aggregation leading to -polymeric coat protein. In the ESR spectra of the 12-SASL probe in dioleoyl phosphatidylcholine (DOPC) bilayers no second protein induced component is observed upon incorporation of M13 coat protein. However, strong effects are detected on the ESR lineshapes upon changing the protein concentration. The ESR lineshapes are simulated by assuming a fixed ratio between the parallel (D) and perpendicular (D) diffusion coefficients of 4, and an order parameter equal to zero. It is found that increasing the protein concentration from L/P to L/P 15 results in a decrease of the rotational diffusion coefficient D from 3.4 × 107 to 1.9 × 107 s–1. In the time-resolved fluorescence experiments with DPH-propionic acid as a probe, it is observed that increasing the M13 coat protein concentration causes an increase of the two fluorescent lifetimes, indicating an increase in bilayer order. Analysis of the time-resolved fluorescence anisotropy decay allows one to quantitatively determine the order parameters P2 and P4, and the rotational diffusion coefficient D of the fluorescent probe. The order parameters P2 and P4 increase from 0.34 to 0.55 and from 0.59 to 0.77, respectively, upon adding M13 coat protein to DOPC bilayers with an L/P ratio of 35. The rotational diffusion coefficient D of the DPH-propionic acid probe decreases on incorporating M13 coat protein, in accordance with the ESR results. It is concluded that M13 coat protein in the -monomeric state is not able to produce a long living lipid boundary shell and consequently an immobilization of the lipids. An overall effect on the lipids is induced, resulting in a reduction in the dynamics and an increase in average lipid order. The hydrophobic region of M13 coat protein is proposed to perfectly match the lipid bilayer, resulting in a relatively small distortion of the bilayer structure of the lipid system. 相似文献
88.
The feeding habits of the filter-feeding fairy shrimp Streptocephalus proboscideus are documented experimentally by offering them ciliates, Volvox, rotifers, nematodes and small crustaceans as prey. Escape capabilities (e.g. swimming speed) rather than size or shape were found to determine these animals' vulnerability to predation by the fairy shrimp. Ingestion rates for Volvox increased hyperbolically with size and, at the high temperatures in which they live, fairy shrimps may daily remove the equivalent of their body weight from the environment. 相似文献
89.
Johan Verreth 《Hydrobiologia》1990,203(1-2):53-61
To elucidate the effect of the horizontal distribution of different zooplankton populations on the accuracy of population density estimates in a fish pond, 40 samples were taken according to a rectangular grid which divided the pond into 5 longitudinal rows and 10 transversal columns. The zooplankton consisted of 55% copepods (mainly Acanthocyclops viridis), 43% cladocerans (mainly Daphnia longispina and Bosmina longirostris) and 2% Rotatoria. The index of patchiness was mostly higher than 1, revealing a strongly clumped distribution. B. longirostris and D. longispina aggregated in the centre of the pond, exhibiting a shore avoiding behaviour. Chydoridae and Ceriodaphnia quadrangula were concentrated in the littoral zone. Besides this habitat related dispersion, a more passive wind induced distribution was detected for most taxonomic groups. Copepod nauplii were concentrated at the leeward side of the pond while elder copepod stages of A. viridis were found in higher densities at the windward end. Based on the calculated coefficients of variation, a table of the accuracies of the density estimates in relation to the number of samples was presented. For more detailed studies on a particular species population, about 25 samples (column samples of 10 L each) are needed to obtain an accuracy varying between 10 an 20%, depending upon the taxonomic group. A slightly higher precision can be obtained, however at a strongly increasing effort. For the practice of fish farming, two to five sample stations should suffice to estimate the total zooplankton abundance with a 30 to 10% accuracy respectively. 相似文献
90.