The Antiplatelet Effect and Chemical Activity of N6-Chloroadenosine Phosphate

Biophysics - A technology has been developed for the preparation of novel chloramine compounds related to adenosine derivatives. The optical absorption characteristics of...     

The role of myeloperoxidase, a product of the polymorphonuclear leukocytes, in the pathogenesis of cataract]

The capacity of myeloperoxidase which is the product of polymorphonuclear leucocytes to induce the lens opacity was studied in young and old rabbits. It was found that the injection of myeloperoxidase solution into anterior chamber of the eye causes the irreversible lens opacification in old rabbits, not in young ones. Light microscopy of the lens section has shown the following alterations: the local thickening of the anterior capsule, disorderly accumulation of epithelial cells, formation of so-called "bladder cells" under the lens epithelium. Changes in experimental eyes are typical for cataract.     

D-glyceraldehyde-3-phosphate dehydrogenase purified from rabbit muscle contains phosphotyrosine.

Homogeneous preparations of D-glyceraldehyde-3-phosphate dehydrogenase purified from rabbit muscle were found to contain 0.2-0.7 moles of covalently bound phosphate per mole of the enzyme. With the use of anti-phosphotyrosine antibodies, evidence was obtained that the enzyme is phosphorylated at tyrosine residues.     

Peroxidation of phosphatidylcholine and cholesterol in mixed monolayers]

Peroxidation of phosphatidylcholine and cholesterol in mixed monolayers at the air-water surface is studied. It is shown that the rate of phosphatidylcholine peroxidation is abruptly decreased in the presence of cholesterol.     

European checkerspots (Melitaeini: Lepidoptera,Nymphalidae) are not aposematic – the point of view of great tits (Parus major)

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Family 28 carbohydrate-binding module of the thermostable endo-1,4-β-glucanase CelD from <Emphasis Type="Italic">Caldicellulosiruptor bescii</Emphasis> maximizes enzyme activity and irreversibly binds to amorphous cellulose

The nucleotide sequence of a chromosome fragment of the thermophilic anaerobic bacterium Caldicellulosiruptor bescii (syn. Anaerocellum thermophilum) has been determined. The fragment contains four open reading frames with the second encoding a 749 aa multimodular endo-1,4-β-glucanase CelD (85019 Da). The N-terminal region of the protein includes a signal peptide and a catalytic module of glycoside hydrolase family 5 (GH5), followed by a carbohydrate-binding module of family 28 (CBM28). The C-terminal region bears three SLH modules. The recombinant endoglucanase and its two separate modules, the catalytic module and CBM28, were produced in E. coli cells and purified to homogeneity. An analysis of the catalytic properties showed CelD to be an endo-1,4-β-glucanase with maximum activity on barley β-glucan at pH 6.2 and 70°C. The enzyme was stable at 50°C for 30 days. Upon removal of the C-terminal CBM28, the activity of GH5 was decreased on cellulose substrates, and its thermostability has dropped. Binding of CBM28 to amorphous cellulose has been almost irreversible as it could not be removed from this substrate in a range of pH of 4–11, temperatures of 0–75°C, and NaCl concentrations of 0–5 M. Only 100% formamide or 1% SDS have been able to remove the protein.     

A comparative spin trapping study of the interaction of hypobromous and hypochlorous acids with <Emphasis Type="Italic">tert</Emphasis>-butyl hydroperoxide

Hypochlorite (HOCl/OCl^?) and hypobromite (HOBr/OBr^?) are shown to react with tert-butyl hydroperoxide with close rate constants (10.8 and 8.9 M^?1 s^?1, respectively). Using a spin trap α-(4-pyridyl-1-oxide)-N-tert-butyl nitrone, both reactions are shown to proceed through decomposition of the hydroperoxide yielding butylperoxyl [˙OOC(CH₃)₃] and butoxyl [˙OC(CH₃)₃] radicals in a ratio depending on the hydroperoxide concentration. Thus, like hypochlorite, hypobromite can generate free radicals in reactions with organic hydroperoxides, which can be important for intensification of free-radical processes, e.g., lipid peroxidation at the chain branching stage.     

Dimers generated from tetrameric phosphorylating glyceraldehyde-3-phosphate dehydrogenase from Bacillus stearothermophilus are inactive but exhibit cooperativity in NAD binding

Tetrameric phosphorylating glyceraldehyde-3-phosphate dehydrogenase (GAPDH) from Bacillus stearothermophilus has been described as a "dimer of dimers" with three nonequivalent interfaces, P-axis (between subunits O and P and between subunits Q and R), Q-axis (between subunits O and Q and between subunits P and R), and R-axis interface (between subunits O and R and between subunits P and Q). O-P dimers, the most stable and the easiest to generate, have been created by selective disruption of hydrogen bonds across the R- and Q-axis interfaces by site-directed mutagenesis. Asp-186 and Ser-48, and Glu-276 and Tyr-46, which are hydrogen bond partners across the R- and Q-axis interfaces, respectively, have been replaced with glycine residues. All mutated residues are highly conserved among GAPDHs from different species and are located in loops. Both double mutants D186G/E276G and Y46G/S48G were dimeric, while all single mutants remained tetrameric. As previously described [Clermont, S., Corbier, C., Mely, Y., Gerard, D., Wonacott, A., and Branlant, G. (1993) Biochemistry 32, 10178-10184], NAD binding to wild type GAPDH (wtGAPDH) was interpreted according to the induced-fit model and exhibited negative cooperativity. However, NAD binding to wtGAPDH can be adequately described in terms of two independent dimers with two interacting binding sites in each dimer. Single mutants D186G, E276G, and Y46G exhibited behavior in NAD binding similar to that of the wild type, while both dimeric mutants D186G/E276G and Y46G/S48G exhibited positive cooperativity in binding the coenzyme NAD. The fact that O-P dimer mutants retained cooperative behavior shows that (1) the P-axis interface is important in transmitting the information induced upon NAD binding inside the O-P dimer from one subunit to the other and (2) the S-loop of the R-axis-related subunit is not directly involved in cooperative binding of NAD in the O-P dimer. In both O-P dimer mutants, the absorption band of the binary enzyme-NAD complex had a highly decreased intensity compared to that of the wild type and, in addition, totally disappeared in the presence of G3P or 1,3-dPG. However, no enzymatic activity was detected, indicating that the formed ternary enzyme-NAD-G3P or -1, 3-dPG complex was not catalytically efficient. In the O-P dimers, the interaction with the S-loop of the R-axis-related subunit is disrupted, and therefore, the S-loop should be less structured. This resulted in increased accessibility of the active site to the solvent, particularly for the adenosine-binding site of NAD. Thus, together, this is likely to explain both the lowered affinity of the dimeric enzyme for NAD and the absence of activity.     

Comparative assessment of resting myocardial perfusion in patients with postinfarct cardiosclerosis by electron-beam tomography and 99mTc-MIBI myocardial single-photon tomography

The purpose of the study was to compare myocardial perfusion assessed by electron beam computed tomography (EBCT) with that obtained by 99mTc-sestamibi single photon emission computed tomography (SPECT) in patients with old myocardial infarction and control subjects at rest. A total of 42 patients with suspected and known ischaemic heart disease (IHD) were included in the study. 20 pts had a history of Q-wave myocardial infarction (MI), 12 pts had an old non-Q-wave MI and 10 served as controls (without perfusion defects on SPECT images at rest). Assessment of the myocardial perfusion by EBCT was performed using the short axis view and multislice mode (MSM) during injection of 50 ml of the nonionic contrast medium at 4 ml/s via cubital vein. Perfusion defects were localized by SPECT according to 6-segment model of the LV (septal, anterior, lateral, posterior, inferior and apical). Overall concordance between EBCT and SPECT was 67% for normal versus abnormal perfusion. Agreement between the 2 methods for each of the 6 segments was 81% (K = 0.62) for the anterior segment, 71% (K = 0.42) for the septal segment, 71% (K = 0.43) for the apical, 69% (K = 0.3) for the lateral segment, 48% (K = 0.13) for the posterior segment and 60% (K = -0.13) for the inferior segment. Discrepancies between the two of techniques were most notable in the posterior region. Beam hardening during passage of the contrast medium through the heart chambers and descending aorta is possible explanation of the artifacts on EBCT images. This study demonstrates that nowadays EBCT is not yet alternative to SPECT in the assessment of the myocardial perfusion in patients and further improvements of scanning techniques are necessary.