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排序方式: 共有270条查询结果,搜索用时 31 毫秒
51.
52.
The role of singlet oxygen in bilirubin photo-oxidation 总被引:8,自引:0,他引:8
A F McDonagh 《Biochemical and biophysical research communications》1971,44(6):1306-1311
53.
G W Lynch H S Slayter B E Miller J McDonagh 《The Journal of biological chemistry》1987,262(4):1772-1778
Thrombin activation of platelets induces the release of a high molecular weight glycoprotein, thrombospondin. On treatment with factor XIII transglutaminase and [3H]putrescine, thrombospondin undergoes specific incorporation of this labeled amine, with 2-3 mol of putrescine being incorporated per mol of thrombospondin. Analysis of plasmin digests of [3H]putrescine-thrombospondin showed that the Mr 53,000-core peptide contains the glutamine site for amine incorporation. In the absence of amine substrate, thrombospondin was found to provide both donor (glutamine) and acceptor (lysine) sites for intermolecular cross-links by factors XIIIa, and high molecular weight protein complexes were formed. Homopolymers of thrombospondin were also observed by electron microscopy. Thrombin-cleaved thrombospondin has more cross-linking sites accessible for [3H]putrescine incorporation or for cross-linkage to itself than does the uncleaved native protein. Examination of thrombospondin cross-linkage in the presence of other protein substrates (fibronectin, collagen, fibrinogen, and von Willebrand factor) for factor XIIIa, resulted in reduced thrombospondin polymer formation. Electron microscopy and autoradiography of fibrin clots formed in the presence of 125I-thrombospondin showed an association of thrombospondin with fibrin fibrils. However, confirmation that this association involves covalent epsilon-(gamma-glutamyl)lysyl cross-links between thrombospondin and fibrin was not obtained. 相似文献
54.
Influence of Ca2+ on the structure of reptilase-derived and thrombin-derived fibrin gels. 总被引:1,自引:0,他引:1
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The effects of Ca2+ ion on the structure of thrombin-derived and reptilase-derived fibrin gels formed at various ionic strengths were studied turbidimetrically. For both enzymes clotting times were shorter, final gel turbidities were higher and fibre mass/length ratios were increased as the ionic strength was lowered. The addition of 5 mM-Ca2+ augmented each of these effects for any given ionic strength. In the thrombin system, Ca2+ increased the final gel turbidity from 0.04 to 0.26 A632.8 at ionic strength 0.15. Under identical conditions in the reptilase system, the final gel turbidity increased from 0.03 A632.8 in the absence of Ca2+ to 0.345 A632.8 in the presence of 5 mM-Ca2+. In the thrombin system, fibre mass/length ratios increased from 0.4 X 10(12) to 6.9 X 10(12) Da/cm in the absence of Ca2+, and from 4.4 X 10(12) to 7.9 X 10(12) Da/cm in the presence of Ca2+, as the ionic strengths were decreased from 0.15 to 0.08 and to 0.11 respectively. In the reptilase system, the mass/length ratios increased from 0.9 X 10(12) to 5.8 X 10(12) Da/cm in the absence of Ca2+, and from 4.8 X 10(12) to 8.7 X 10(12) Da/cm in the presence of Ca2+, as the ionic strengths were decreased from 0.15 to 0.08 and to 0.10 respectively. At ionic strengths below 0.10, the presence of 5 mM-Ca2+ caused precipitation and macroscopic aggregation of fibrinogen upon the addition of either enzyme. In the presence of 5 mM-Ca2+, the fibres composing thrombin-induced and reptilase-induced gels were virtually identical. 相似文献
55.
P. F. McDonagh 《The Yale journal of biology and medicine》1983,56(4):303-311
The aim of thrombolysis, angioplasty, and coronary artery bypass surgery is to "reperfuse" ischemic myocardium; however, reperfusion can cause further cardiac damage and compromise the coronary microcirculation. Because nutrient supply and exchange and delivery of pharmacologic agents require a patent microvasculature, the coronary microcirculation plays a major role in myocardial recovery from ischemia. It is known that ischemia-reperfusion can cause an increase in coronary permeability and microvascular plugging (No-reflow). The permeability to macromolecules is increased more than the permeability to smaller molecules. The permeability increase leads to extravasation of plasma proteins and a permeability edema. Furthermore, proteins that normally remain extravascular are now free to wash out the heart. Both microvascular effects, increased coronary permeability and No-reflow, compromise cardiac function. The degree of damage depends on the nature (No-flow versus low-flow) and length of ischemia. Unfortunately, both the increase in coronary permeability and the reduction in perfused capillarity advance with time during early reperfusion. Although the increase in permeability does not require the presence of platelets or leukocytes, it is apparent that the No-reflow response does. Mechanisms that may explain the microvascular responses to ischemia include cell swelling, damage caused by oxygen free radicals, and inflammatory responses that may or may not involve granulocytes. The permeability response may involve a calcium-mediated endothelial contraction because the macromolecular leakage that follows ischemia can be prevented by pretreating hearts with the calcium blocker nisoldipine. Protection of the coronary microcirculation should be included in any attempt to improve treatment of occlusive coronary artery disease. 相似文献
56.
The effect of plasmin on the subunit polypeptides of factor XIII has been investigated. purified human plasma (a2b2) and platelet (a2) zymogens and the enzyme (a2) were incubated with plasmin at plasmin: factor XIII ratios of 0.03-0.5 casein units per mg protein. Under conditions in which plasmin readily digested fibrinogen and casein, it had no effect on either a2b2 or a2. There was no evidence for cleavage of peptide bonds in the zymogens, and all the potential catalytic activity was retained after prolonged incubation. Similarly a2*, either in the presence or absence of b subunit, was also unaffected by plasmin incubation. 90% of the activity was recovered after incubation of factor XIII with plasmin. b subunit was also not degraded. Additionally, no evidence was obtained that plasmin could activate factor Xiii. These results indicate that in purified systems there is no significant interaction between plasmin and factor XIII. 相似文献
57.
T D Elich A F McDonagh L A Palma J C Lagarias 《The Journal of biological chemistry》1989,264(1):183-189
Etiolated Avena seedlings grown in the presence of 4-amino-5-hexynoic acid, an inhibitor of 5-aminolevulinic acid synthesis in plants, contain less than 10% of the spectrally detectable levels of phytochrome found in untreated seedlings (Elich, T.D., and Lagarias, J.C. (1988) Plant Physiol. 88, 747-751). In this study, incubation of explants from such seedlings with [14C]biliverdin IX alpha led to rapid covalent incorporation of radiolabel into a single 124-kDa polypeptide in soluble protein extracts. Immunoprecipitation experiments confirmed that this protein was phytochrome. Parallel experiments were performed with four unlabeled linear tetrapyrroles, the naturally occurring biliverdin IX alpha isomer, two non-natural isomers, biliverdin XIII alpha and biliverdin III alpha, and phycocyanobilin-the cleaved prosthetic group of the light-harvesting antenna protein C-phycocyanin. In all cases, except for the III alpha isomer of biliverdin, a time-dependent recovery of photoreversible phytochrome was observed. The newly formed phytochrome obtained after incubation with biliverdin IX alpha exhibited spectral characteristics identical with those of the native protein. In contrast, the spectral properties of phytochromes formed during incubation with biliverdin XIII alpha and phycocyanobilin differed significantly from those of the native chromoprotein. These results indicate that biliverdin IX alpha is an intermediate in the biosynthesis of the phytochrome chromophore and that phytochromes with prosthetic groups derived from bilatrienes having non-natural D-ring substituents are photochromic. 相似文献
58.
F. Villagra C. B. Cooke M. J. N. McDonagh 《European journal of applied physiology and occupational physiology》1993,67(6):549-553
These experiments investigated the oxygen consumption and work efficiency of adults and children performing identical movement patterns. Adult men (mean age 24) and male children (mean age 12) performed squatting exercises with and without a pause at the lowest point of the squat. The former were termed no rebound squats and the latter were termed rebound squats. Subjects performed the exercises without load and with loads equal to 5%, 10% and 15% of body mass.The results showed that the children consumed 10% more oxygen per unit total body mass than the adults. The gross efficiency of the adults was significantly greater than that of the children. Net and apparent efficiencies were not significantly different between the age groups. Gross and net efficiencies declined with load. Rebound squats required 13% less oxygen than no rebound squats. The gross, net and apparent efficiency of rebound squats was significantly greater than that of no rebound squats. It is suggested that the greater gross efficiencies of adults is related to their lower basal metabolic rate and that the greater efficiency of rebound exercise is related to the storage of energy in elastic tissues. 相似文献
59.
60.
Raynner RD Barboza Wedson de MS Souto José da S Mourão 《Journal of ethnobiology and ethnomedicine》2007,3(1):1-14