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Assembly properties of two CNBr fragments of avian desmin that correspond to the headpiece domain and helix 1B 总被引:2,自引:0,他引:2
To study how different domains of the muscle-specific intermediate filament protein, desmin, contribute to its polymerization, two of its CNBr fragments were examined as to their oligomeric structure under assembly conditions. One of these, D88, covers residues 1-88 and represents almost the entire headpiece; the other, D109, covers residues 145-254, and includes the entire Helix 1B and part of linker L12 of the intact molecule. Chemical cross-linking followed by SDS-PAGE, and analytical gel filtration, revealed that in 10 mM Tris-HCl, pH 8.5, conditions that favor tetramerization of intact desmin D88 formed only dimers. D109, on the other hand, formed primarily a dimeric species but low levels of trimeric and tetrameric species were also detectable. These data are consistent with the proposal that, during assembly of intact protein molecules into IF, the headpiece and Helix 1 contribute to dimerization of two polypeptides into a parallel, in-register coiled-coil. However, additional interactions, including headpiece-to-rod binding and hydrophobic interaction along the entire rod domain, are required to stabilize the tetramers and full-size IF. 相似文献
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Selenocysteine's mechanism of incorporation and evolution revealed in cDNAs of three glutathione peroxidases 总被引:5,自引:0,他引:5
G T Mullenbach A Tabrizi B D Irvine G I Bell J A Tainer R A Hallewell 《Protein engineering》1988,2(3):239-246
The nonsense codon, UGA, has for the first time recently been shown to encode selenocysteine in two proteins, mouse glutathione peroxidase (GSH-Px) (EC 1.11.1.9) and bacterial formate dehydrogenase. A co-translational rather than post-translational selenium-incorporation mechanism has been implicated. Furthermore, high expression levels of GSH-Px have suggested that suppression of termination is efficient and specific. We have isolated and characterized pituitary, kidney and placenta cDNAs for bovine, human and mouse GSH-Px respectively. It is demonstrated that this novel suppression event occurs in diverse tissues, in at least three mammalian species and at the translational step. Surprisingly, GSH-Px is shown to be extramitochondrially encoded, indicating a cytosolic suppression event rather than one utilizing the mitochondria's well-documented extended codon-reading ability. Sequence analysis reveals that a simple proximal contextual pattern responsible for readthrough does not exist. Analysis of predicted secondary structures of mRNAs, however, has revealed a conformation which may be unique to selenocysteine proteins and may prove useful as a tool for artificial incorporation of selenocysteines. A human intron for GSH-Px from an unspliced mRNA has been isolated whose position indicates an ancient, divergent evolutionary relationship with thioredoxin-S2, rather than an independent convergent one. 相似文献
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In this study we describe the discovery and characterization of a substance in human amniotic fluid that stimulates prostaglandin biosynthesis by a microsome-enriched preparation of bovine seminal vesicles. The stimulatory activity is not retained substantially upon anisotropic ultrafiltration through a filter with a molecular weight exclusion limit of 500. Stimulation of prostaglandin biosynthesis by this substance is time- and concentration-dependent; maximal stimulation of approx. 200% being observed within 20 min of commencing incubation with 1 ml-equivalent of stimulant fraction. Stimulatory activity is demonstrable both in the presence of reduced glutathione (1.3 mM) and L-tryptophan (20 mM), either separately or combined, and in the presence of exogenous arachidonic acid (5-120 microM). In the absence of added cofactors, the stimulatory substance increases the rates of biosynthesis of prostaglandin E2 and prostaglandin F2 alpha to equal extents. The amount of stimulatory substance added to incubations is correlated positively with increased oxygen consumption during incubations. The stimulatory substance is stable to heating at 100 degrees C for 10 min but is inactivated substantially (to less than 20% of original activity) by treatment with pronase. It is concluded that human amniotic fluid contains a substance of relatively low molecular weight, which is proteinaceous in character, that stimulates prostaglandin endoperoxide synthase activity. 相似文献
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Benzyl 2-acetamido-2-deoxy-3-O-methyl-α-d-glucopyranoside (3) was obtained by deacetalation of its 4,6-O-benzylidene derivative (2). Compound 2 was prepared by methylation of benzyl 2-acetamido-4,6-O-benzylidene-2-deoxy-α-d-glucopyranoside with methyl iodide-silver oxide in N,N-dimethylformamide. Diol 3 was selectively benzoylated and p-toluenesulfonylated, to give the 6-benzoic and 6-p-toluenesulfonic esters (4 and 5, respectively). Displacement of the sulfonyl group of 5 with sodium benzoxide in benzyl alcohol afforded the 6-O-benzyl derivative (6). Glycosylation of 4 with 2,3,4,6-tetra-O-acetyl-α-d-galactopyranosyl bromide (7) in dichloromethane, in the presence of 1,1,3,3-tetramethylurea, furnished the disaccharide derivative 8. Similar glycosylation of compound 6 with bromide 7 gave the disaccharide derivative 10. O-Deacetylation of 8 and 10 afforded disaccharides 9 and 11. The structure of compound 9 was established by 13C-n.m.r. spectroscopy. Hydrogenolysis of the benzyl groups of 11 furnished the disaccharide 2-acetamido-2-deoxy-4-O-β-d-galactopyranosyl-3-O-methyl-d-glucopyranose (N-acetyl-3-O-methyllactosamine). 相似文献
6.
A versatile and simple continuous-culture apparatus is described. With this apparatus, independent control of limiting growth factors and other nutrilites is possible and the conditions of each experiment are reproducible. In view of the synchronized speed of the feeder syringes, flow variation troubles are not encountered. The device allows the performance of growth experiments at different dilution rates simultaneously in a single run which makes the comparison of the results more reliable. The operation of the device has been tested successfully with a study of adenine deaminase induction in yeast. 相似文献
7.
Summary Petiolar felt-sheath of palm (Livistona chinensis) has been successfully used as a new biostructural matrix for the immobilization of fungal hyphae. The reticulated felt-sheath is made up of fibrous bundles having irregularly scattered membranous-foliose and fibrous outgrowths woven into a cohesive multi-layered mesh. Immobilization of Aspergillus niger was achieved with both spore and hyphal suspensions as the inoculum. Growth in immobilized cultures was 19% greater than in free cultures. 相似文献
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