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891.
The presence of superoxide dismutase in bovine and human milk was investigated by ultrafiltration, gel filtration, and isoelectric focusing. Conclusive evidence for the presence of this enzyme in both milks is presented. The molecular weight of the enzyme was estimated by gel filtration on Sephadex G-100 to be 30,000, which is consistent with reported values for the copper, zinc form of superoxide dismutase. In addition, enzyme activity was inhibited by cyanide, thus eliminating the possibility that the enzyme was present in the manganese form. Several isoenzymes were detected by isoelectric focusing in polyacrylamide gel, and the isoenzyme pattern in bovine milk was the same as that found for bovine plasma, suggesting that milk superoxide dismutase originates from plasma. It may be that the presence of copper, zinc superoxide dismutase in milk is important for the maintenance of its oxidative stability.  相似文献   
892.
A method to quantitate lectin activity based on hemagglutination assay in microtiter plates is described. In addition to the normal method of visual titer evaluation an electronic particle counter is used for counting of nonagglutinated cells in the microtiter wells; this allows a rapid, quantitative determination of the amount of lectin required to agglutinate 50% of the countable single cells. It is also recommended that counting results should be related to a standard curve of concanavalin A to improve the reproducibility of the assay.  相似文献   
893.
The anion-binding characteristics of ferredoxin from Halobacterium of the Dead Sea have been studied by 35Cl? NMR. It is found that the binding constant of Cl? to halophilic ferredoxin is ca. 0.09 at 28 °C and that the binding enthalpy is positive. It is also found that the correlation time for chloride ions bound to halophilic ferredoxin is about 10 ns. The effect on the 35Cl?1 NMR signal of adding competing anions is also studied. Halophilic proteins like ferredoxin which have a high negative charge bind anions with low affinity but the 35Cl? quadrupole relaxation technique can conveniently monitor such weak binding.  相似文献   
894.
A new technique, the quantitative determination of total enzyme concentrations by specific immunoprecipitation with purified, radioiodinated antibodies, was used to investigate the presence and possible roles of inactive enzyme in the regulation of chalcone synthase. Dark-grown cell suspension cultures from parsley (Petroselinum hortense) contained neither catalytically active nor detectable amounts of immunoprecipitable chalcone synthase. Irradiation induced large increases and subsequent decreases of both. Significant differences in the peak positions and in the half-lives of active and total chalcone synthase indicated that induced cells contained inactive as well as active enzyme forms. The presence of inactive enzyme could be explained by two different modes of regulation, (i) simultaneous de novo synthesis of active and inactive enzyme (“Simultaneous Model”), or (ii) de novo synthesis of active enzyme only, with sequential steps of inactivation and degradation (“Sequential Model”). Both models were compatible with experimental results, as analyzed mathematically by investigating the relations between curves for rate of enzyme synthesis, enzyme activity, total enzyme, and half-lives of active and total enzyme. However, the “Simultaneous Model” postulated that de novo synthesis of inactive enzyme represented always the vast majority of total enzyme synthesis, while the Sequential Model integrated inactive enzyme with facility in a sequence of irreversible inactivation and degradation of active enzyme. Experiments with repeated induction indicated that cells containing large amounts of inactive enzyme increased enzyme activity by de novo synthesis rather than by activation of preexisting inactive enzyme.  相似文献   
895.
Temporal and regional aspects of early neural crest cell migration in relation to extracellular matrix (ECM) organization and distribution in the embryonic axolotl trunk were studied by light microscopy, TEM, and SEM. The dominating structure of the interstitial ECM is a complex network of fibrils, which are indicated by ruthenium red staining to consist of collagen in association with ruthenium red-positive components, probably including glycosaminoglycans. The ECM fibrils, which are largely used as substratum for locomotion by the crest cells, have a temporally and regionally specific organization and distribution. Increase in ECM fibrils on the neural tube, ahead of the crest cell front, is correlated with initiation of crest cell emigration, and it is suggested that the fibrils may stimulate this process by providing a suitable substratum for cell locomotion. An increase in ECM fibrils in extracellular spaces surrounding the crest cell population is correlated with an expansion of these spaces and with progressing crest cell migration into them. It is proposed that the spatial organization of the ECM fibrils influences crest cell shape and orientation during early migration.  相似文献   
896.
The roles of rabbit liver cytochrome b5, epoxide hydrase and various forms of cytochrome P-450 in the NADPH-dependent metabolism of benzo(a)pyrene were examined. After incorporation of the purified enzymes into phospholipid vesicles, using the cholate gel filtration technique, the various types of cytochrome P-450 did exhibit different stereospecificities in the oxygenation of the substrate. Cytochrome P-450LM2 was found to efficiently convert benzo(a)pyrene in the presence of epoxide hydrase to 4,5-dihydroxy-4,5-dihydrobenzo(a)pyrene whereas cytochrome P-450LM4 primarily participated in the formation of 9,10-dihydroxy-9,10-dihydrobenzo(a)pyrene. By contrast, benzo(a)pyrene was not metabolized by cytochrome P-450LM3. Cytochrome b5 enhanced cytochrome P-450LM2-catalyzed oxygenations 5-fold, whereas cytochrome P-450LM4-dependent oxygenations proceeded at a 3 times higher rate when cytochrome b5 was present in the membrane.  相似文献   
897.
A slow reacting substance, produced by murine mastocytoma cells, has been shown to have the structure 5(S)-hydroxy-6(R)-S-glutathionyl-7,9,11-trans-14-cis-eicosatetraenoic acid (11-trans leukotriene C, previously referred to as leukotriene C-2) by ultraviolet spectroscopy, amino acid analyses, lipoxygenase conversion and comparisions with a synthetic compound of known structure and stereochemistry.  相似文献   
898.
Slow reacting substance (SRS), produced by rat peritoneal mononuclear cells after stimulation with ionophore A23187, consists of two main components (Bach, M.K. et al. (1979) J. Immunol. 122, 160–165). One of these components was recently identified as leukotriene C-1. The other component has now been identified as leukotriene D.  相似文献   
899.
Preparations of RuBP carboxylase are shown to carry out an oxygen dependent decarboxylation of L-3-phosphoglyceric acid. The product of this reaction is probably phosphoglycollate. L-3-phosphoglyceric acid, formed by RuBP carboxylase is therefore proposed to be the primary substrate for photorespiration.  相似文献   
900.
Heparin, heparan sulphate, and various derivatives thereof have been oxidised with periodate at pH 3.0 and 4° and at pH 7.0 and 37°. Whereas oxidation under the latter conditions destroys all of the nonsulphated uronic acids, treatment with periodate at low pH and temperature causes selective oxidation of uronic acid residues. The reactivity of uronic acid residues depends on the nature of neighbouring 2-amino-2-deoxyglucose residues. d-Glucuronic acid residues are susceptible to oxidation when flanked by N-acetylated amino sugars, but resistant when adjacent residues are either unsubstituted or N-sulphated. L-Iduronic acid residues in their natural environment (2-deoxy-2-sulphoamino-d-glucose) are resistant to oxidation, whereas removal of N-sulphate groups renders a portion of these residues periodate-sensitive. Oxidised uronic acid residues in heparin-related glycans may be cleaved by alkali, producing a series of oligosaccharide fragments. Thus, periodate oxidation-alkaline elimination provides an additional method for the controlled degradation of heparin.  相似文献   
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