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1.
Galloway RE  Mets L 《Plant physiology》1982,70(6):1673-1677
A uniparentally inherited 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU)-resistant mutant of Chlamydomonas reinhardii, Dr2, which has a resistance mechanism of the type defined as `primary,' has been isolated. In vitro Hill reactions catalyzed by isolated thylakoid membranes reveal a reduced apparent affinity of the thylakoids for DCMU. These changes in membrane properties quantitatively account for the resistance of mutant Dr2 to herbicide inhibition of growth. The properties of this mutant show that all of the Hill reaction-inhibiting DCMU binding sites are under identical genetic control. Mutant Dr2 is a useful new uniparental genetic marker, since it has a novel phenotype and it may be possible to identify its altered gene product. The low cross-resistance of Dr2 to atrazine suggests that there may be considerable flexibility in exploiting induced herbicide resistance of crop plants for improving herbicide specificity.  相似文献   

2.
Maximum levels of binding of α-bungarotoxin to foetal human brain membranes were found to remain essentially constant at 30–50 fmol/mg protein (1.1–1.5 pmol/g wet weight in whole brain) between gestational ages of 10 and 24 weeks. Equilibrium binding of α-bungarotoxin to both membranes and to detergent extracts showed saturable specific binding to a single class of sites with Kd (app) values of 3.5 × 10?9 M and 2.4 × 10?9 M respectively. Association rate constants, determined from time courses of binding of α-bungarotoxin to membranes and detergent extracts, were 2.3 × 105 M?1 sec?1 and 2.6 × 105 M?1 sec?1 respectively. Dissociation of α-bungarotoxin from both membrane and detergent extracts showed a rapid initial rate with T12 approx 15 min which, in the case of the detergent extract, was followed by a slower dissociation accounting for the remaining 20% of the bound ligand. Competition studies with a number of cholinergic ligands indicated that the α-bungarotoxin-binding sites in foetal brain display a predominantly nicotinic profile.  相似文献   

3.
Two mutant strains (denoted as DCMUr-I and DCMUr-II) of theblue-green alga Aphanocapsa 6714, capable of growing in thepresence of 10–5 M DCMU (an inhibitor of electron transporton the acceptor side of photosystem II), were isolated. The DCMU sensitivity of growth rates and of two photosystemII activities, O2 emission and fluorescence, was investigatedin the mutant cells and compared with that of the wild type.The DCMU sensitivity of isolated thylakoids was also studied.The sensitivity of the mutant cells to other DCMU-type inhibitors(o-phenanthroline and atrazine) was tested. The results suggest that strain DCMUr-I resistance could bedue to the acquisition of a cellular permeability barrier toDCMU, expressed only after an adaptation phase in the presenceof the inhibitor. DCMUr-II resistance seems to be due primarilyto an alteration of the thylakoid membranes of the photosyntheticapparatus itself. (Received June 4, 1979; )  相似文献   

4.
Somatostatin binding to pituitary plasma membranes.   总被引:3,自引:0,他引:3  
A method has been developed for the study of somatostatin binding to anterior pituitary plasma membranes. When 5×10?9M [125I]Tyr1-somatostatin (SA 18 Ci/mmol) was incubated with isolated pituitary plasma membranes (protein = 100 μg), 13.6% of total radioactivity was bound excluding nonspecific binding. The Scatchard plot could be resolved into two distinct components and analyzed to yield: K1diss = 3.3×10?8M and K2diss = 7.7×10?6M. This binding was shown to be specific for somatostatin.  相似文献   

5.
The specific binding of [3H] Prostaglandin (PG) F2α to bovine corpus luteum cell membranes prepared in homogenizing buffer containing either 1 mM EDTA (H-EDTA) or 1 mM Ca2+ (HCa2+) was examined. The membranes prepared in H-EDTA buffer bound less [3H] PGF2α and had a single class of PGF2α receptors with an apparent dissociation constant (Kd) of 2.7 × 10?8M. The addition of Ca2+ to these membranes resulted in increased binding with the appearance of new PGF2α receptors of Kd = 4.3 × 10?9M. The membranes prepared in HCa2+ buffer contained two classes of receptors with Kds = 2.9 × 10?9M and 2.9 × 10?8M. The removal of Ca2+ from these membranes resulted in lower binding as well as a complete disappearance of receptors of Kd = 2.9 × 10?9M. These results suggest the dependency of high affinity PGF2α receptors, in bovine corpus luteum cell membranes, on cations.  相似文献   

6.
Results from this study indicate that adult rat brain posesses guanylate cyclase activity sensitive to serotonin (5-HT) and localized in the synaptic plasma membrane. The enzyme appears to have multiple activation sites for 5-HT with specific activity maxima at the 5-HT concentrations of 5 × 10?10M and 7 × 10?8M respectively. The rates of guanosine-3′:5′-monophosphate (cyclic GMP) formation at these concentrations of 5-HT are, respectively, 170% and 307% above the endogenous or basal production rate of 2.7±0.3picomoles/minute/milligram of synaptosomal membrane protein. We have also been able to identify four distinct types (Type #1, #2, #3, and #4) of high affinity, specific binding sites for 5-HT on isolated synaptosomal membranes from rat brain. Dissociation constants of 2.6 × 10?10M, 2.5 × 10?9M, 7.0 × 10?9M, and 4.6 × 10?8M, characterize the binding of 5-HT to our sites of Type #1 through Type #4 respectively. The specific, high affinity binding was saturated at 5-HT concentrations of 5 × 10?10M for the Type #1 sites, 5 × 10?9M for our Type #2 sites, 1 × 10?8M for our Type #3 sites, and 7 × 10?8M for our Type #4 sites. The 5-HT concentrations producing saturation of our specific binding sites of Type #1 and Type #4 are virtually identical to those that elicit the two maxima of 5-HT stimulated cyclic GMP production, indicating that a membrane-bound guanylase cyclase may be closely associated with certain 5-HT receptors and/or re-uptake sites.  相似文献   

7.
Abstract— The specific interaction of S-100 protein with disrupted synaptosomes was further investigated. The specific binding is a saturable and reversible process, and is time, temperature, and strictly Ca2+ -dependent. Two affinities affect the interaction (Kins= 7.04 × 10?9 M. 1.28 × 1012 binding sites/ mg protein; Kins2= 3.91 × 10?7M, 2.96 × 1013 binding sites/mg protein). The half-saturation time is about 5.5 min at 37°C. The half-life of the complex is 17 min at 37°C. At 0°C the binding is 75% slower than at 37° C, and only one-third of the binding sites are involved. The binding capacity is decreased by high NaCl concentrations and by pretreating membranes at high temperatures. Digestion of membranes with trypsin practically abolishes the specific binding. Treatment of membranes with phospholipase C decreases the specific binding, while phospholipase D enhances it to some extent. Other lipid extractors decrease significantly the extent of the interaction. Synaptic plasma membranes seem to be the synaptosomal component involved in the high affinity binding. The S-100 binding activity seems to undergo developmental changes, the adult values of kinetic parameters being reached around the 16th postnatal day in the rat. The results are discussed also in relation to the membrane-bound fraction of S-100.  相似文献   

8.
Triiodothyronine, reverse triiodothyronine and thyroxine were found to inhibit 125I labelled thyrotropin binding to human thyroid plasma membranes in vitro. Both the thyrotropin binding and the effect of the above iodoamino-acids on this binding were pH, temperature and time dependent, 50% inhibition of thyrotropin binding was observed at 2×10?7M concentration of reverse triiodothyronine or thyroxine and at 1.1 × 10?6M concentration of triiodothyronine. The kinetic studies of thyrotropin binding revealed that the maximal capacity of receptor sites for the pituitary hormone is unaffected by the presence of thyroid hormones. On the other hand the association and dissociation constants for thyrotropin binding changed when iodoaminoacids were present in the incubation medium /Ka 8.13 × 107M?1 vs 1.6 × 108M?1 and Kd 1.14 × 10?8M vs 4.55 × 10?9M respectively, depending on the pH/. The double reciprocal plots showed competitive mechanism of inhibition. The present study suggest that triiodothyronine, reverse triiodothyronine and thyroxine are able to modify the thyrotropin binding to membrane receptors.  相似文献   

9.
3H-nicotine binding was performed on intact and solubilized rat brain membranes as well as membranes from the electric organ of the Torpedo fish. The Kd for binding to intact and solubilized rat brain membranes was 5.6 × 10?9 M and 1.1 × 10?8M respectively, and the binding capacity 2.0 × 10?14 and 3.0 × 10?13 moles /mg protein respectively. The Kd for Torpedo membranes was 3.1 × 10?7M and the binding capacity 6.8 × 10?13 moles/mg protein. The binding was stereospecific with the affinity of the (?)-nicotine being about 8 times greater than the (+)-nicotine with all three preparations. The relative affinity for the nicotine binding site of nicotinic cholinergic drugs was considerably less in rat brain than in Torpedo membranes, where the sites are mainly cholinergic. A comparison was made of the ability of a variety of cholinergic drugs and nicotine derivatives to compete with 3H-nicotine binding and their relative pharmacologic potency to produce or inhibit a characteristic prostration syndrome caused by (?)-nicotine administered intraventricularly to rats. From such studies it was concluded that nicotine, in part, may be interacting at noncholinergic sites in rat brain.  相似文献   

10.
The cell membranes exhibited specific binding to 3H-prostaglandin E1 (3H-PGE1) and 125I-human chorionic gonadotropin (125I-HCG). Unlabeled PGE1,PGE2 (1.4 × 10?7M), PGF and PGF (1.4 × 10?5M) decreased 3H-PGE1 binding by more than 80%. The binding of 125I-HCG was completely inhibited by 5 × 10?8M unlabeled HCG. However, the unlabeled PGE1 (1.15 × 10?6M) and HCG (8.4 × 10?7M) had no effect on 125I-HCG and 3H-PGE1 binding respectively. A PG antagonist, 7-oxa-13-prostynoic acid, inhibited only 3H-PGE1 binding but not 125I-HCG binding. These results suggest the presence of specific receptors for PGE1 and HCG in the cell membranes and that the binding occurs either at two different sites on the same receptor or that each binds to a “different” receptor molecule.  相似文献   

11.
D T Wong  J S Horng 《Life sciences》1973,13(11):1543-1556
Membranes from homogenates of corpus striatum bound 3H-dihydromorphine in a saturable fashion with a Km value of 1 × 10?9M. The binding of 3H-dihydromorphine to the membranes was reduced to about 10% by 10?7M levorphanol but not by 10?7M dextrorphan. The binding of 3H-dihydromorphine became less sensitive to 10?7M levorphanol when the concentration of 3H-dihydromorphine was greater than 2 × 10?9M. Other opiate narcotics, e.g. morphine and l-methadone, were as effective as levorphanol in competition for the binding 3H-dihydromorphine with ED50 values of 2–4 × 10?9M. d-Methadone and dextrorphan were about 1/50 and 1/2000 as effective as their respective levo-isomers. The opiate antagonist, naloxone, also competed effectively for the binding sites with an ED50 value of 3.3 × 10?9M. Substances like acetylcholine, choline, serotonin, norepinephrine and dopamine were ineffective. Only ionophores specific for divalent cations stimulated the binding of 3H-dihydromorphine suggesting that some endogenous divalent cations may be inhibitory to the binding of the opiate narcotic. The receptors of 3H-dihydromorphine probably exist in the membranes of nerve endings and have a density of 6 × 1012 sites per g in corpus striatum. We conclude that the described technique can successfully detect the opiate narcotic receptors in the central nervous system without the usual method of displacement.  相似文献   

12.
Two herbicide-resistant mutants of the unicellular cyanobacterium, Anacystis nidulans R2, were obtained by mutagenesis with N-methyl-N′-nitro-N-nitrosoguanidine. These mutants, A. nidulans R2D1 and R2D2, were selected by growth of mutagenized cells in the presence of 10?6 M and 10?5 M 3-(3,4-dichlorophenyl)-1,1-dimethyl urea (DCMU), respectively. Both were found to be cross-resistant to 2-chloro-4-ethylamino-6-isopropylamino-s-triazine (atrazine) and 2-n-heptyl-4-hydroxyquinoline-n-oxide (HQNO) by measurement of Photosystem II activity in the presence of the inhibitors. The DCMU-resistance trait from each mutant was transferred to a wild-type genetic background by DNA-mediated transformation of A. nidulans cells. The two resulting transformants, A. nidulans R2D1-X1 and R2D2-X1, were similar to the original mutants with respect to DCMU- and HQNO-resistance. However, both exhibited increased sensitivity to atrazine relative to the mutants from which they were derived. Polyacrylamide gel electrophoretic analysis revealed that the mutants and transformants were deficient in a 34 kDa, surface-exposed polypeptide which was present in the wild-type strain; the transformants exhibited a new polypeptide of 35.5 kDa which was also highly surface-exposed.  相似文献   

13.
《Plant science》1986,46(1):5-10
Cyanobacterin, a secondary metabolite produced by the cyanobacterium, Scytonema hofmanni, inhibits the growth of algae and plants. This compound is a potent inhibitor of photosynthetic electron transport and acts at a site in photosystem II (PS II). To further define the site of action of cyanobacterin, the effects of this natural product were investigated in a herbicide-resistant mutant of the cyanobacterium, Anacystis nidulans R2D2-X1. A. nidulans R2D2-X1 was reported to grow and maintain photosynthetic electron transport in the presence of 20 μM 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) and 6.0 μM atrazine. Resistance was attributed to an altered 32 kDa (quinone-binding, QB) protein [6]. In the presence of Hill electron acceptors, K3Fe(CN)6 and dichlorophenol-indophenol (DCPIP), spheroplasts of A. nidulans R2D2-X1 were inhibited by cyanobacterin at the same concentration as wild type spheroblasts. Under these same conditions, spheroplasts of the mutant maintained their resistance to DCMU. Similar results were obtained with isolated thylakoid membranes. In contrast, silicomolybdate reduction, which is resistant to DCMU inhibition, was very sensitive to cyanobacterin. We conclude that cyanobacterin inhibits electron transport in PS II at a unique site which is different from that of DCMU.  相似文献   

14.
U Gehring  G M Tomkins 《Cell》1974,3(1):59-64
Mouse kidney cytosol contains specific receptors that reversibly bind dihydrotestosterone at a concentration of 43 f moles/mg protein. [Nonstandard abbreviation: DHT, dihydrotestosterone, 17 β-hydroxy-5 α-androstan-3-one.] The equilibrium dissociation constant of the receptor-dihydrotestosterone complex is 1.3 × 10?9M for females and 1.7 × 10?9M for castrated males. The complex sediments at 8–9S in glycerol gradients. In males bearing the androgen-insensitivity mutation (analogous to human testicular feminization), the specific dihydrotestosterone receptor activity is decreased about 8 fold. The residual binding activity has wild type affinity (KD = 1.5 × 10?9M) for dihydrotestosterone and also sediments at 8–9S. Kidney cytosol from castrated mutant mice displays a new binding component with low affinity and high capacity for dihydrotestosterone.  相似文献   

15.
Membrane receptors for Vicia graminea (Vg) lectin on human red cells were analyzed using deoxycholate lysates obtained from 125I-erythrocyte membranes incubated with a purified lectin immobilized on Sepharose 4B. The glycoproteins (GP) specifically bound to the gel were eluted and analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and autoradiography. Using native erythrocytes the results obtained demonstrate that N red cells have exposed Vg receptors located on GPα (synonym glycophorin A) and GPδ (synonym glycophorin B) whereas on M erythrocytes the Vg receptors are restricted to GPδ. The presence of Vg receptors was also found on the hybrid glycoprotein (made of the N-ter of GPδ and C-ter of GPα) carried by St(a+) erythrocytes. A similar amount of radioactivity was bound to Vg-Sepharose incubated with neuraminidase-treated N or M membranes. The material eluted was tentatively identified as asialo GPα and asialo GPδ, suggesting that numerous receptors have been uncovered mainly on asialo GPα species from M erythrocytes. No glycoprotein component could be identified from the material eluted from Vg Sepharose incubated with native or neuraminidase-treated membrane from a Tn(+) individual. Scatchard plot analysis obtained from binding experiments at equilibrium with M, N, and St(a+) cells revealed the existence of at least two classes of receptors both on native and neuraminidase-treated erythrocytes. Desialylation of the M, N, and St(a+) erythrocytes resulted in an increase in the number of low- and high-affinity binding sites but had no significant effect on the association constants. However, high-affinity binding constants were about six times higher with N (7.07 × 107 and 6.61 × 107m?1 for native and neuraminidase-treated N cells, respectively) as compared to M erythrocytes (1.13 × 107 and 1.17 × 107m?1 for native and neuraminidase-treated M cells, respectively) whereas the low-affinity binding constants were similar for all types of cells (in the range of 0.1 to 0.3 × 107m?1). The number of Vg binding sites increases from 0.085 × 105 to 0.8 × 105 (high affinity) and from 2.10 × 105 to 6.25 × 105 (low affinity) per native and neuraminidase-treated N cell, respectively. On native and neuraminidase-treated M cells the number of Vg receptors increases from 0.011 × 105 to 0.51 × 105 (high affinity) and 0.13 × 105 (low affinity), respectively. The large increase in the number of Vg receptors on neuraminidase-treated M cells is correlated with a large increase in agglutinability. Under similar treatment St(a+) cells behave like N erythrocytes whereas only 0.16 × 105 Vg receptors of low affinity could be detected on neuraminidase-treated Tn erythrocytes. The results demonstrate that sialic acid is not required for binding and favor the view that the binding site of V. graminea lectin accommodates with two types of erythrocyte membrane receptors, one including both a contribution of polypeptide and oligosaccharide chains and a second which involves a simple interaction with sugar sequence Galβ1–3GalNAc available only when sialic acids are removed. The latter disaccharide is recognized by the Arachis hypogea lectin which therefore inhibits further binding of the V. graminea to neuraminidase-treated erythrocytes.  相似文献   

16.
The binding characteristics and the inhibitory power of atrazine and DCMU towards uncoupled electron flow activity were studied in acyl lipid-depleted thylakoid membranes from atrazine-susceptible and-resistant biotypes of Solanum nigrum L. For this purpose, phospholipase A2 from Vipera russelli and the lipase from Rhizopus arrhizus were used to obtain a selective lipid class (phospholipids or galactolipids) depletion which was restricted to the outer monolayer. Neither phospholipid nor galactolipid removal affected the dissociation constant and the number of binding sites of atrazine. In contrast, the dissociation constant of DCMU was increased in phospholipid-depleted thylakoid membranes but remained unchanged after galactolipid depletion. The number of DCMU binding sites decreased significantly after both lipase treatments, but only in the resistant biotype. The inhibitory effectiveness of the herbicide was either decreased or increased (to different extents) depending on the lipid class which was removed from the membrane and on the biotype considered. These results are discussed with reference to the possible conformational changes of the 32 kDa herbicide-binding polypeptide occurring after lipase treatments.Abbreviations Atrazine 2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine - BSA bovine serum albumin - DCMU diuron, 3-(3,4-dichlorophenyl)-1,1-dimethylurea - DGDG digalactosyldiacylglycerol - LRa lipase from Rhizopus arrhizus - MGDG monogalactosyldiacylglycerol - PC phosphatidylcholine - PG phosphatidylglycerol - PLA2 phospholipase A2 - R atrazine-resistant - S atrazinesusceptible  相似文献   

17.
The rate of [3H]dopamine binding to crude synaptic membranes from canine caudate nucleus was considerably increased by 2 mM ATP, 5′-adenylylimidodiphosphate and GTP or by 1 mM 5′-guanylyl-imidodiphosphate, while strongly inhibited by 2 mM ADP and GDP. Half maximal concentrations of [3H]dopamine to bind to the membranes were 1.11 × 10?7M and 8.75 × 10?6M in the absence of 4 mM ATP, indicating a negative cooperativity of the dopamine receptor, and 9.25 × 10?7 M in its presence. Hill coefficient was increased from 0.70 to 1.04 by addition of 4 mM ATP. The optimal concentration of ATP for [3H]dopamine binding was in the range of 0.5 to 5 mM.  相似文献   

18.
Streptomyces lividans 1326 carries inducible mercury resistance genes on the chromosome, which are arranged in two divergently transcribed operons. Expression of the genes is negatively regulated by the repressor MerR, which binds in the intercistronic region between the two operons. The merR gene was expressed in E. coli using a T7 RNA polymerase/promoter expression system, and MerR was purified to around 95% homogeneity by ammonium sulfate precipitation, gel filtration and affinity chromatography. Gel filtration showed that the native MerR is a dimer with a molecular mass of 31?kDa. Two DNA binding sites were identified in the intercistronic mer promoter region by footprinting experiments. No evidence for cooperativity in the binding of MerR to the adjacent operator sequences was observed in gel mobility shift assays. The dissociation constants (KD) for binding of MerR were: binding site I, 8.5?×?10?9?M; binding site II, 1.2?×?10?8?M; and for the complete promoter/operator region 1?×?10?8?M. The half-life of the MerR-DNA complex was 19.4?min and 18.8?min for binding site I and binding site II, respectively. The KD value for binding of mercury(II)chloride to MerR, again determined by mobility shift assay, was 1.1?×?10?7?M.  相似文献   

19.
Escherichia coli heat-stable enterotoxin (STa) was found to bind on the surface of human colonic (COLO 205) cells. The binding of [125I]STa to cell membranes was found to be specific, reversible and saturable. Scatchard analysis of the equilibrium binding demonstrated a single class of binding sites with a Kd of 0.5×10−10 M. Autoradiographic analysis of polyacrylamide gel electrophoresis revealed the specific incorporation of [125I]STa into a single STa binding protein with a molecular mass of 95 kDa. Following incubation of COLO 205 cells with STa, a rise of intracellular cGMP was also evident.  相似文献   

20.
The effect of hormone-like compounds at different concentrations: 2,4-D (2 × 10?6; 2 × 10?5; and 2 × 10?4M) and 1-NAA (2 × 10?7; 2 × 10?6; 2 × 10?5; 4 × 10?5, and 6 × 10?5 M) on the growth and production of phenolic compounds, including flavans and lignin, was investigated in callus culture of tea plant (Camellia sinensis L., a highly productive strain IFR ChS-2). The growth of the culture was vigorous, and production of phenolic compounds therein was efficient in the medium containing 2 × 10?5 M 2,4-D. Substitution of 1-NAA for 2,4-D in all the cases decelerated the growth of the culture. These changes were more pronounced when 2 × 10?7 and 2 × 10?6 M 1-NAA was used; in this case, biomass accumulation decreased by 1.5–2.0 times as compared with control material growing on the medium with 2 × 10?5 M 2,4-D. In the presence of 1-NAA, the content of total soluble phenolic compounds and flavans in the calli rose by 30% on the average as compared with control material. Accumulation of lignin remained essentially the same. Therefore, the replacement of 2,4-D with 1-NAA in the nutrient medium used for the growing of highly productive strain of tea plant callus did not induce considerable changes in its ability to produce phenolic compounds.  相似文献   

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