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1.
Three peaks of methyltransferase activity specific for MNNG alkylated DNA have been identified from extracts of chemically adapted M. luteus. They are designated as TI to TIII in order to their elution from a Sephadex G-75 column. The first one of these peaks has been purified to homogeneity. TI, is an inducible, unusually salt resistant, heat labile protein which corrects O6-methylguanine in alkylated DNA by the transfer of the O6-alkyl group to a cysteine amino acid in the TI protein. There is a stoichiometric relationship between the loss of O6-methylguanine from the DNA and the production of S-methylcysteine. Partially purified TII & TIII proteins show specificity for O4-alkylthymine and methyl phosphotriesters respectively. The mode of repair by the isolated methyltransferases is similar yet there is no competition for substrate specificity. The apparent molecular weights of TI, TII & TIII proteins are 31Kd, 22Kd, and 13Kd respectively. 相似文献
2.
Summary Studies with the atypical muscarinic antagonist pirenzepine provide convincing evidence for the classification of muscarinic acetylcholine receptors (mAChRs) into two subtypes, M1 and M2. The present study examines the heterogeneity of the M2 subtype employing the newly developed competitive muscarinic antagonist, AFDX-116. Comparison of the binding affinities of pirenzepine, atropine, and AFDX-116 to mAChRs in microsomes from the rabbit cerebral cortex, heart, and iris smooth muscle shows that iris mAChRs, which are pharmacologically of the M2 subtype, can be distinguished from M2 cardiac receptors based on their affinity for AFDX-116. These results are consistent with the hypothesis that the M2 receptor subtype consists of a heterogeneous population of receptors.Abbreviations mAChRs
Muscarinic Acetylcholine Receptors
- CCh
Carbachol
- NMS
N-Methylscopolamine
- AFDX-116
11-[[2-[(diethylamino)methyl]-1-piperidinyl]acetyl]-5,11-dihydro-6Hpyrido[2,3-b][1,4]benzodiazepine-6-one 相似文献
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4.
Abstract: Effects of the neuropeptide corticotropin-(1–24) -tetracosapeptide (ACTH) on the endogenous and exogenous phosphorylation of lipids and endogenous phosphorylation of proteins were investigated in microsomes and a 110,000 ×g supernatant fraction [30–50% (NH4)2SO4 precipitate; ASP30–50] obtained from rabbit iris smooth muscle. Subcellular distribution studies revealed that both of these fractions are enriched in diphosphoinositide (DPI) kinase. The 32P labeling of lipids and proteins was measured by incubation of the subcellular fractions with [γ-32P]ATP. The labeled lipids, which consisted of triphosphoinositide (TPI), DPI, and phosphatidic acid (PA) were isolated by TLC. The microsomal and ASP30–50 fractions were resolved into six and nine labeled phosphoprotein bands, respectively, by sodium dodecyl sulfate polyacrylamide gel electrophoresis. The basal labeling of both lipids and proteins was rapid (30–60 s), and it was dependent on the presence of Mg2+ in the incubation medium; in general it was inhibited by high concentrations (>0.2 mM) of Ca2+. ACTH stimulated the labeling of TPI and inhibited that of PA in a dose-dependent manner, with maximal effect observed at 50–100 μ of the peptide. ACTH appears to increase TPI labeling by stimulating the DPI kinase. Under the same experimental conditions ACTH (100 μM) inhibited significantly the endogenous phosphorylation of six microsomal phosphoproteins (100K, 84K, 65K, 53K, 48K, and 17K). In the ASP30–50 fraction, ACTH inhibited the phosphorylation of three phosphoproteins (53K, 48K, and 17K) and stimulated the labeling of six phosphoprotein bands (117K, 100K, 84K, 65K, 42K, and 35K). The effects of ACTH on lipid and protein phosphorylation are probably Ca2+-independent; thus the neuropeptide effects were not influenced by either 1 μM EGTA or low concentrations of Ca2+ (50 μ.M). We conclude that a relationship may exist between polyphosphoinositide metabolism and protein phosphorylation in the rabbit iris smooth muscle. 相似文献
5.
Drought is an important environmental factor that can affect rhizobial competition and N2 fixation. Three alfalfa (Medicago sativa L. and M. falcata L.) accessions were grown in pots containing soil from an irrigated (Soil 1) and a dryland (Soil 2) alfalfa field in northern
Utah, USA. Mutants of three strains of Rhizobium meliloti Dang. from Pakistan (UL 136, UL 210, and UL 222) and a commercial rhizobial strain 102F51a were developed with various levels
of resistance to streptomycin. Seeds inoculated with these individual streptomycin-resistant mutants were sown in the two
soils containing naturalized rhizobial populations. Soils in the pots were maintained at −0.03, −0.5, and −1.0 MPa. After
10 weeks, plants were harvested and nodule isolates were cultured on agar medium with and without streptomycin to determine
nodule occupancy (proportion of the nodules occupied by introduced rhizobial strains). Number of nodules, nodule occupancy,
total plant dry weight, and shoot N were higher for Soil 1 than Soil 2. Number of nodules, plant dry weight, and shoot N decreased
as drought increased from −0.03 to −1.0 MPa in the three alfalfa accessions. Rhizobial strains UL 136 and UL 222 were competitive
with naturalized alfalfa rhizobia and were effective at symbiotic N2 fixation under drought. These results suggest that nodulation, growth, and N2 fixation in alfalfa can be improved by inoculation with competitive and drought-tolerant rhizobia and may be one economically
feasible way to increase alfalfa production in water-limited environments.
Joint contribution from USDA-ARS and the Utah Agric. Exp. Sta., Utah State Univ., Logan, UT 84322-4810, USA. Journal Paper
No. 4931.
Joint contribution from USDA-ARS and the Utah Agric. Exp. Sta., Utah State Univ., Logan, UT 84322-4810, USA. Journal Paper
No. 4931. 相似文献
6.
Requirement for calcium ions in acetylcholine-stimulated phosphodiesteratic cleavage of phosphatidyl-myo-inositol 4,5-bisphosphate in rabbit iris smooth muscle 总被引:18,自引:11,他引:7
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1. The mechanism of acetylcholine-stimulated breakdown of phosphatidyl-myo-inositol 4,5-bisphosphate and its dependence on extracellular Ca(2+) was investigated in the rabbit iris smooth muscle. 2. Acetylcholine (50mum) increased the breakdown of phosphatidylinositol bisphosphate in [(3)H]inositol-labelled muscle by 28% and the labelling of phosphatidylinositol by 24% of that of the control. Under the same experimental conditions there was a 33 and 48% increase in the production of (3)H-labelled inositol trisphosphate and inositol monophosphate respectively. Similarly carbamoylcholine and ionophore A23187 increased the production of these water-soluble inositol phosphates. Little change was observed in the (3)H radioactivity of inositol bisphosphate. 3. Both inositol trisphosphatase and inositol monophosphatase were demonstrated in subcellular fractions of this tissue and the specific activity of the former was severalfold higher than that of the latter. 4. The acetylcholine-stimulated production of inositol trisphosphate and inositol monophosphate was inhibited by atropine (20mum), but not tubocurarine (100mum); and it was abolished by depletion of extracellular Ca(2+) with EGTA, but restored on addition of low concentrations of Ca(2+) (20mum). 5. Calcium-antagonistic agents, such as verapamil (20mum), dibenamine (20mum) or La(3+) (2mm), also abolished the production of the water-soluble inositol phosphates in response to acetylcholine. 6. Release of inositol trisphosphate from exogenous phosphatidylinositol bisphosphate by iris muscle microsomal fraction (;microsomes') was stimulated by 43% in the presence of 50mum-Ca(2+). 7. The results indicate that increased Ca(2+) influx into the iris smooth muscle by acetylcholine and ionophore A23187 markedly activates phosphatidylinositol bisphosphate phosphodiesterase and subsequently increases the production of inositol trisphosphate and its hydrolytic product inositol monophosphate. The marked increase observed in the production of inositol monophosphate could also result from Ca(2+) activation of phosphatidylinositol phosphodiesterase. However, there was no concomitant decrease in the (3)H radioactivity of this phospholipid. 相似文献
7.
R Agarwal M Athar D R Bickers H Mukhtar 《Biochemical and biophysical research communications》1990,173(1):34-41
In recent years, choloroaluminum phthalocyanine tetrasulfonate (A1PCTS) has been shown to be a promising photosensitizer for the photodynamic therapy (PDT) of cancer. Although its mechanism of photodynamic action is not well defined, A1PCTS is going to be under clinical trials of PDT. In this study, in vitro addition of A1PCTS to a suspension of rat epidermal microsomes followed by irradiation with red light (approximately 675 nm) resulted in significant destruction of cytochrome P-450 and associated monooxygenase activities. The photodestructive effect was dependent on both the dose of A1PCTS and the duration of light exposure. Studies using various quenchers of reactive oxygen species showed that only scavengers of singlet oxygen such as histidine, 2,5-dimethylfuran, beta-carotene and sodium azide afforded substantial protection against photodestruction. Our data indicate the direct involvement of singlet oxygen in the A1PCTS-mediated photodestructive process. 相似文献
8.
9.
Amin Ghafuri-Esfahani Rahman Shokri Athar Sharifi Lida Shafiee Roya Khosravi 《Preparative biochemistry & biotechnology》2020,50(8):834-841
AbstractSeveral factors may affect erythropoietin (EPO) sugar structures including designing cell culture procedure, pH, concentration of additives, dissolved oxygen, and other physicochemical parameters. In this study, we investigated the influence of changes in effective parameters and compounds on the growth rate of Chinese hamster ovary cell (CHO) cells producing recombinant EPO. Cell culture was performed at different temperature, buffering conditions, and varied concentrations of additives such as pyruvic acid, insulin, GlutaMAX, and sodium butyrate. Results indicated that the optimal temperature and pH were 37?°C and 7.2, respectively. Also, optimal concentrations for pyruvic acid, butyrate, glutamate, and insulin were obtained to be 20?mM, 1?mM, 2?mM, and 40?μg/mL, respectively. Then, cell culture was performed in microcarrier-coated spinner flasks under the optimized condition. The results showed recombinant human EPO (rhEPO) production with adequate purity. Optimization of physicochemical conditions and culture media are important factors to improve the quantity and quality of protein products. This study showed that cell growth and recombinant EPO protein production significantly increased under the optimized conditions. The results of this research can also be used in scale-up to increase the efficiency of EPO production. Abbreviations: EPO: erythropoietin; CHO cell: Chinese hamster ovary cell; rhEPO: recombinant human EPO; DMEM: modified eagle’s medium; FBS: fetal bovine serum; SDS-PAGE: sodium dodecyl sulfate–polyacrylamide gel electrophoresis; IGF-1: insulin-like growth factor 1 相似文献
10.
Molecular Biology Reports - Alzheimer’s disease (AD) is a neurodegenerative old age disease that is complex, multifactorial, unalterable, and progressive in nature. The currently approved... 相似文献