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101.
The specificity of thermitase (EC 3.4.21.14), a microbial thermostable serine proteinase fromThermoactinomyces vulgaris, with several oligo- and polypeptide substrates was investigated. Preferred hydrolysis of peptide bonds with a hydrophobic amino acid at the carboxylic site was observed. The proved carboxypeptidolytic splitting of Leu5-enkephalin and bradykinin, as well as the noncleavability of casomorphins by thermitase, can be explained by the position of the glycine and proline residues in these substrates. Major cleavage sites in the oxidized insulin B chain in a 15-min incubation with thermitase at Gln4-His5, Ser9-His10, Leu11-Val12, Leu15-Tyr16 and in the oxidized insulin A chain at Cys SO3H11-Ser12, Leu13-Tyr14, and Leu16-Glu17 were observed. Additional cleavages of the bonds His5-Leu6, Arg22-Gly23, Phe24-Phe25, Phe25-Tyr26, and Tyr26-Thr27 in the oxidized B chain and Cys SO3H6-Cys SO3H7 and Tyr19-Cys SO3H20 in the oxidized A chain in 2-h incubations with thermitase were also noted. Hydrolysis of salmine A I component in a 10-min incubation was observed mainly at four peptide bonds: Arg5-Ser6, Ser6-Ser7, Arg18-Val19, and Gly27-Gly28. The cleavage sites of thermitase in both insulin chains were similar to those reported in the studies of subtilisins. 相似文献
102.
Seven microbial peptide inhibitors—chymostatin, antipain, elastatinal, leupeptin, pepstatin, bestatin, and phosphoramidon—were tested for their efficiency to inhibit thermitase, a thermostable serine protease fromThermoactinomyces vulgaris. Chymostatin and antipain were the most effective inhibitors, with Ki values of 7×10–8
M and 2×10–7
M, respectively. Except for leupeptin, all inhibitors resist hydrolysis by thermitase. Leupeptin, however, is cleaved by thermitase between the two leucylresidues. Further, a close relationship in specificity between thermitase and subtilisin BPN and their distinct discrimination from elastase specificity was demonstrated by using these inhibitors. 相似文献
103.
Schönheit Peter Beimborn Dieter B. Perski Hans-Joachim 《Archives of microbiology》1984,140(2-3):247-251
Cultures of Methanobacterium thermoautotrophicum (Marburg) growing on media low in potassium accumulated the cation up to a maximal concentration gradient ([K+]intracellular/[K+]extracellular) of approximately 50,000-fold. Under these conditions, the membrane potential was determined by measuring the equilibrium distribution of the lipophilic cation (14C) tetraphenylphosphonium (TPP+). This cation was accumulated by the cells 350-to 1,000-fold corresponding to a membrane potential (inside negative) of 170–200 mV. The pH gradient, as measured by equilibrium distribution of the weak acid, benzoic acid, was found to be lower than 0.1 pH units (extracellular pH=6.8). The addition of valinomycin (0.5–1 nmol/mg cells) to the culture reduced the maximal concentration gradient of potassium from 50,000-to approximately 500-fold, without changing the membrane potential. After dissipation of the membrane potential by the addition of 12C-TTP+ (2 mol/mg cells) or tetrachlorosalicylanilide (3 nmol/mg cells), a rapid and complete efflux of potassium was observed.These data indicate that potassium accumulation in the absence of valinomycin is not in equilibrium with the membrane potential. It is concluded that at low extracellular K+ concentrations potassium is not accumulated by M. thermoautotrophicum via an electrogenic uniport mechanism.Non-common abbreviations TPP+
Tetra phenylphosphonium bromide
- DTE
Dithioerythritol
- TCS
3,5,3,4-Tetrachlorosalycylanilide 相似文献
104.
105.
The herbicides amiprophosmethyl (APM) trifluralin, and oryzalin as well as the fungicides methylbenzimidazolyl carbamate (MBC), O-isopropyl N-phenyl carbamate (IPC), and chlorisopropyl N-phenyl carbamate (CIPC), which are known to cause the destruction of microtubules in vivo but do not interfere with tubulin polymerization in vitro, have been examined with respect to their ability to affect Ca2+ transport in isolated cell organelles. In contrast to colchicine which has no effect on Ca2+ transport in isolated mitochondrial and microsomal fractions, all of the substances investigated caused considerable reduction of ca2+ net uptake into mitochondrial but not into microsomal fractions. This reduction has been shown to be due to an increase in passive Ca2+ efflux. These results have been extrapolated to in vivo situations where they are postulated to act by raising cytoplasmic Ca2+ levels.Abbreviations APM
amiprophosmethyl
- CIPC
chlorisopropyl N-phenyl carbamate
- IPC
O-isopropyl N-phenyl carbamate
- MBC
methylbenzimidazolyl carbamate
- Mops
3-(N-Morpholino) propanesulfonic acid
- DMSO
dimethylsulfoxide 相似文献
106.
Analysis of a drosophila tRNA gene cluster 总被引:23,自引:0,他引:23
107.
A study of the subcellular distribution of radioactivity in rat uterus after injection of labelled corticosterone showed that the radioactivity was observed in all fractions from 5 min. to 120 min. A maximum uptake was observed 10 min. after application of the labelled steroid. Competitive uptake of radioactive progesterone and unlabelled corticosterone was assayed 10 min. after injection of the hormone mixture. The ratio between radioactive progesterone and unlabelled corticosterone was 1 : 1 and 1 : 2 (moles:moles), respectively. Compared with control experiments with rats which had received radioactive progesterone alone, the results gave evidence that progesterone found in all subcellular fractions and in the total homogenate was not depressed by unlabelled corticosterone. However, unlabelled progesterone reduced the tritiated progesterone in uterine tissue. This observation demonstrates that the uptake of progesterone by rat uterus is specific. 相似文献
108.
Effects of Indoleacetic Acid on the Quantity of Mitochondria, Microbodies, and Plastids in the Apical and Expanding Cells of Dark-grown Oat Coleoptiles 总被引:1,自引:1,他引:0 下载免费PDF全文
We determined the number of mitochondria, microbodies, and plastids in dark-grown oat (Avena sativa) coleoptiles following incubation in indoleacetic acid (IAA) for a period of 60 minutes at 6-minute intervals. In the apical outer epidermis of coleoptiles, the mitochondria increased from 31.4 to 35 per cell section with a 6-minute incubation in IAA, and this trend persisted over the 60-minute incubation. Neither the microbodies, plastids, nor the dicytosomes (Gawlik and Miller 1974 Plant Physiol 54:217-221) responded to the hormone. The apical parenchyma showed no change in quantity of any of the organelles including the dictyosomes during IAA incubation. The quick response of mitochondria in the coleoptile tip could be interpreted as an association of this organelle with hormone transport, growth, or perhaps with gravity perception. In the subapical expansion region, IAA caused significant reductions of mitochondria, microbodies, and dictyosomes in the outer epidermis compared to the control, the timing of which preceded the IAA-induced elongation and of geotropism. The fast response of organelles in the various cells is probably a change in organelle volume rather than number. That microbodies show a response to the plant hormone in the permanently achlorophyllous epidermis indicates that these organelles, in addition to their peroxisomal functions in green leaves, also may have a growth regulation function. IAA treatment was without effect on the quantity of the various types of plastids (including the amyloplasts) in the different oat coleoptile cells. 相似文献
109.
Saccharomyces cerevisiae nuclear membranes were prepared from isolated nuclei by digesting chromatin with deoxyribonuclease and ribonuclease, washing of residual nuclei with 0.5 M MgCl2, and discontinuous gradient centrifugation in buffered Ficoll solutions. Electron microscopic examination of the preparations showed single membrane and double membrane vesicles and membrane sheets. Pores or residual pores were often visible. In double membrane profiles the two unit membranes were often separated by the remains of the perinuclear cistern. The nuclear membrane fragments contained 58% protein, 23.8% phospholipid, 6% sterols, 7.1% neutral acylglycerols, 4.8% RNA, and 0.3% DNA. The phospholipid content of the membrane preparations was influenced by a phospholipase activity with acidic pH optimum. 相似文献
110.
Eberhard Spieß Beatrice Neuer Dieter Werner 《Biochemical and biophysical research communications》1982,104(2):548-556
Distinct polypeptides, 54,000–68,000 daltons in size, are alkali-stably bound to eukaryotic DNA. DNA fragments several hundred base pairs in length associated with these polypeptides are preferentially retained on glass fibre filters from solutions containing 1 M sodium chloride. About 50 percent of the protein/DNA complexes present in total DNA are retained on filters together with about 2 percent of the DNA. This preferential binding is demonstrated (a) by the ratio of 3H and 35S radioactivity retained on filters after filtration of DNA from [3H]thymidine and L-[35S]methionine labelled cells, (b) radioiodination of the material retained on filters and passing filters respectively and (c) by electron microscopical visualisation of the polypeptide component in the complexes after chemical modification with dinitrofluorobenzene (DNFB) followed by incubation with dinitrophenyl (DNP) specific antibodies. 相似文献