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1.
T H Nahm S W Lee A Fausto Y Sonn L V Avioli 《Biochemical and biophysical research communications》1979,89(2):396-402
Serum and hepatic 25-hydroxyvitamin D (25OHD), and serum calcium, phosphate, 25OHD3 binding capacity and binding affinity were measured in male and female trout. Both serum and hepatic 25OHD levels are decreased in female trout with elevations in protein bound calcium and phosphate. Whereas the apparent dissociation constant (Kd) for serum binding of 25OHD3 of 1.0–2.0 × 10?9M is similar in males and females, the 25OHD3 binding capacity of hypercalcemic spawning trout (1.39 × 10?7M) is significantly less than that of male fish (1.88 × 10?7M). At circulating serum concentrations of 25OHD which average 9.5 × 10?9M only 5–7% of trout serum 25OHD binding sites are occupied. 相似文献
2.
Thomas L. Rost 《Journal of Plant Growth Regulation》1984,3(1-4):51-63
Intact and excised cultured pea roots (Pisum sativum L. cv Alaska) were treated with chlorsulfuron at concentrations ranging from 2.8 ×10?4 M to 2.8×10?6 M. At all concentrations this chemical was demonstrated to inhibit the progression of cells from G2 to mitosis (M) and secondarily from G1 to DNA synthesis (S). The S and M phases were not directly affected, but the transition steps into those phases were inhibited. Total protein synthesis was unaffected by treatment of intact roots with 2.8×10?6 M chlorsulfuron. RNA synthesis was inhibited by 43% over a 24-h treatment period. It is hypothesized that chlorsulfuron inhibits cell cycle progression by blocking the G2 and G1 transition points through inhibition of cell cycle specific RNA synthesis. 相似文献
3.
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 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
4.
Danijela Z. Krstić Mirjana Čolović Mojca Bavcon kralj Mladen Franko Katarina Krinulović Polonca Trebše 《Journal of enzyme inhibition and medicinal chemistry》2013,28(4):562-573
Inhibition of bovine erythrocyte acetylcholinesterase (free and immobilized on controlled pore glass) by separate and simultaneous exposure to malathion and malathion transformation products which are generally formed during storage or through natural or photochemical degradation was investigated. Increasing concentrations of malathion, its oxidation product malaoxon, and its isomerisation product isomalathion inhibited free and immobilized AChE in a concentration-dependent manner. KI, the dissociation constant for the initial reversible enzyme inhibitor-complex, and k3, the first order rate constant for the conversion of the reversible complex into the irreversibly inhibited enzyme, were determined from the progressive development of inhibition produced by reaction of native AChE with malathion, malaoxon and isomalathion. KI values of 1.3 × 10? 4 M? 1, 5.6 × 10? 6 M? 1 and 7.2 × 10? 6 M? 1 were obtained for malathion, malaoxon and isomalathion, respectively. The IC50 values for free/immobilized AChE, (3.7 ± 0.2) × 10? 4 M/(1.6 ± 0.1) × 10? 4, (2.4 ± 0.3) × 10? 6/(3.4 ± 0.1) × 10? 6 M and (3.2 ± 0.3) × 10? 6 M/(2.7 ± 0.2) × 10? 6 M, were obtained from the inhibition curves induced by malathion, malaoxon and isomalathion, respectively. However, the products formed due to photoinduced degradation, phosphorodithioic O,O,S-trimethyl ester and O,O-dimethyl thiophosphate, did not noticeably affect enzymatic activity, while diethyl maleate inhibited AChE activity at concentrations > 10 mM. Inhibition of acetylcholinesterase increased with the time of exposure to malathion and its inhibiting by-products within the interval from 0 to 5 minutes. Through simultaneous exposure of the enzyme to malaoxon and isomalathion, an additive effect was achieved for lower concentrations of the inhibitors (in the presence of malaoxon/isomalathion at concentrations 2 × 10? 7 M/2 × 10? 7 M, 2 × 10? 7 M/3 × 10? 7 M and 2 × 10? 7 M/4.5 × 10? 7 M), while an antagonistic effect was obtained for all higher concentrations of inhibitors. The presence of a non-inhibitory degradation product (phosphorodithioic O,O,S-trimethyl ester) did not affect the inhibition efficiencies of the malathion by-products, malaoxon and isomalathion. 相似文献
5.
J.K. Sheehan C. Arundel C.F. Phelps 《International journal of biological macromolecules》1983,5(4):222-228
Light scattering and viscometric studies have been carried out on two preparations, A and B, of rooster comb hyaluronate. Sedimentation rate studies have also been performed with A. Light scattering measurements in 0.2 m KCl for preparation A gave a molecular weight of 3.3 × 106 and for B, 1.0 × 106. In (0.1–0.3) M NaCl similar measurements gave a particle weight for A of (4.4–6.4 × 106 and for B (1.7–2.8 × 106. In 0.066 m CaCl2 molecular weight values of 9.5 × 106 for A and 1.7 × 106 for B were obtained. Thus in the presence of Na+ and Ca2+ ions aggregates of chains persisted into dilute solution. Measurements by light scattering on A and B in 4 m guanidinium chloride gave values in the same range as those obtained in 0.2 m KCl. Sedimentation rate studies on A gave values of 10.3 Svedbergs in 0.2 m KCl and 12.2 Svedbergs in 0.2 m NaCl and 0.066m CaCl2. The shear dependence of the viscosity was studied using a conicylindrical viscometer at shear rates between 0.5 and 20 s?1. Preparation A in 0.2 m KCl and NaCl yielded values for (νsp/cc→0 of 5000 and 7100 ml g?1 respectively in keeping with the tendency to aggregate. The behaviour for preparation B was similar. In 0.066 m CaCl2 there was a marked dependence of viscosity on shear speed below 10 s?1 for all concentrations and the value of (νsp/c)→0 at 0 s?1 for preparation A was 7700 ml g?1 while at a shear rate of 8 s?1 (νsp/c)c→0 ? 5000 ml g ?1. Similar effects were found for preparation B and the data suggest associations of chains disruptable by weak shear forces. The increase in viscosity with concentration in the presence of 0.066 m CaCl2 was much less than in the presence of KCl or NaCl, suggesting that the Ca2+ had a marked effect on the ”rigidity’ of the molecules in solution. A viscometric titration experiment with Ca2? showed that a level of 0.02 m CaCl2 in 0.2 m NaCl was sufficient to produce the change in viscosity presented above and that significant perturbations of the viscosity were present at 0.005?0.01 m CaCl2. 相似文献
6.
Inhibition of the neutrophil oxidative response to a chemotactic peptide by inhibitors of arachidonic acid oxygenation 总被引:5,自引:0,他引:5
N-formylmethionylphenylalanine stimulates a short burst of antimycin A-insensitive O2 uptake, O2? production and hexosemonophosphate shunt oxidation of glucose by guinea pig peritoneal neutrophils. The stimulated oxidative metabolism, as well as release of lysosomal enzymes ± cytochalasin B, are inhibited by 5,8,11,14-eicosatetraynoic acid (ID50 1.5 × 10?5 M). High concentrations of indomethacin inhibit the peptide-stimulated oxidations (ID50 1.6 × 10?4 M) while acetylsalicylic acid (2.5 × 10?3 M) does not. Digitonin-stimulated oxidative metabolism and enzyme release are not inhibited by 5,8,11,14-eicosatetraynoic acid or indomethacin at concentrations that depress effects of the N-formylated peptide. 相似文献
7.
William McChesney Moore Robert N. Brady 《Biochimica et Biophysica Acta (BBA)/General Subjects》1976,444(1):252-260
Specific binding of 125I-labeled α-bungarotoxin to a 34 800 × g pellet of a whole rat brain homogenate has been obtained at levels 2 pmol toxin per g of whole brain with a Kd of 8·10?9 M. Binding is reduced 90% by 10?5 M (+)- tubocurarine chloride and 10?4 M nicotine, whereas concentrations of 10?4 M choline chloride, atropine sulfate and eserine sulfate have essentially no effect on toxin binding. These results compare closely with those obtained from binding studies with 125I-labeled α-bungarotoxin and soluble acetylcholine receptor protein preparations form Torpedo nobiliana; suggesting that this mammalian receptor protein is nicotinic in character.Extraction of the 34 800 × g pellet with 1% Emulphogene yields a soluble fraction with specifically binds 125I-labeled α-bungarotoxin with a Kd of 5·10?9 M. Nicotine and α-bungarotoxin at concentrations of 10?5 M abolish toxin- receptor complex formation and carbachol and (+)-tubocurarine chloride reduce complex formation 35–40% at similar concentrations. Eserine sulfate, atropine sulfate, decamethonium, and pilocarpine had no effect on complex formation at concentrations of 10?5 M. 相似文献
8.
Properties of the fully developed phosphate transport system in the fertilized egg of the sea urchin, Strongylocentrotus purpuratus, were investigated. The rates of phosphate transport at concentrations of external phosphate of 1 to 44 μM, both in the absence and in the presence of 100 μM arsenate, exhibit typical saturation kinetics. At sea water concentrations of 2 μM phosphate, the rate of uptake is about 2 × 10?9 μm/egg/minute at 15°C. Arsenate is a competitive inhibitor of phosphate transport, fully and immediately reversible in its effects, yielding Ki values ranging from 10.5 to 14.1 × 10?6 M in comparison to the corresponding apparent KM (Michaelis-Menten) constants for phosphate of 5.6 to 7.5 × 10?6 M (pH 8.0, 15°C). The rate of arsenate uptake in a phosphate deficient medium amounts to 2.8 to 2.9 × 10?10 μm arsenate/egg/minute at an arsenate concentration of 2.9 to 10.2 μM arsenate (HAsO4??), which is 9.5 and 5.6% of the rate of phosphate uptake at corresponding phosphate concentrations. Arsenate has essentially the same developmental effects at initial concentrations of 5–10 μM and 100 μM arsenate, namely no observable effects for exposure periods of 7.5 hours, although longer periods result in blockage of development at the early blastula stage. Outward flux of phosphate ions cannot be demonstrated by washing prelabelled eggs with sea water containing low or high concentrations of phosphate, even when phosphorylation has been blocked by exposing the eggs to a metabolic inhibitor. Phosphate uptake rates measured in the pH range from 5.0 to 10.0 reveal a sharp optimum at pH 8.8–8.9. Reference to the apparent pK' values of the phosphoric acid system indicate that the entering species is the HPO4?? ion. The effects on rates of phosphate uptake of exposure to sea water at pH values between 7 and 10 for 30 minute periods are fully reversible, but at lower pH values, reversal is delayed, and is only partial. Sodium molybdate (0.01 M), sodium pyrophosphate (1.5 × 10?4 M), and adenosine triphosphate (1–5 × 10?4 M) for exposure periods ranging from 40 to 180 minutes did not significantly affect phosphate uptake. Omission of Ca++ ion from artificial sea water is without effect on phosphate uptake but the absence of both Ca++ and Mg++ results in profound and irreversible depression of both phosphate uptake and development. The data of this and the following paper are consistent with the conclusion that the transport of phosphate involves a surface located carrier. The apparent secondary and tertiary ionization constants of phosphoric acid in sea water (ionic strength = 0.6885) were measured, resulting in a value for pK′2 = 6.14 and for pK′3 = 10.99, at 15°C and phosphate at infinite dilution. 相似文献
9.
R Donato 《Journal of neurochemistry》1976,27(2):439-447
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
10.
C V Rao 《Biochemical and biophysical research communications》1975,64(1):416-424
The cell membranes isolated from bovine corpora lutea bound 3H-prostaglandin (PG) F2α with high affinity and specificity. The specific binding of 3H-PGF2α was detectable at 10?10M added 3H-PGF2α and reached saturation at 10?7M to 10?6M. Unlabeled PGF2α, as low as 10?9M, inhibited the binding of 3H-PGF2α with complete inhibition occurring at 10?6M. The Scatchard analysis of equilibrium binding data revealed that the PGF2α receptors are heterogeneous: Kd1?5.1 × 10?9M, n?289 fmoles/mg protein; Kd2?1.8 × 10?8M, n?780 fmoles/mg protein. The relative affinities of various other PGs for binding to PGF2α receptors were (PGF2α?100%): PGF1α?17.5; PGE1?0.8; PGE2?22.4; PGA1?0.007; PGB1?0.01. The specificity and affinity of 3H-PGF2α binding is consistent with the possibility that this receptor interaction may reflect an initial event in the action of PGF2α as a luteolytic agent. 相似文献
11.
Prostacyclin (PGI2) produced a biphasic response in canine isolated basilar arteries. In low doses (1 × 10?8M?1 × 10?7M) PGI2 caused a slight but consistent relaxation of resting muscle tone. In low concentrations (1 × 10?8M?1 × 10?6M) PGI2 antagonized muscle contractions caused by serotonin or prostaglandin (PG) F2α. This relaxant effect with low doses of PGI2 on the isolated cerebral artery contrasts with findings obtained with other PGs and supports the hypothesis that PGI2 is a mediator of vasodilatation. However, in 1 × 10?5M concentrations PGI2 contracted the arterial muscle and did not antagonize contractions induced by serotonin or PGF2α. 相似文献
12.
Intact human platelets bind cytochalasin B (CB) with a capacity of 100– 120 p mols CB/mg protein or approximately 7 × 104 molecules/cell and dissociation constants (KD) ranging from 2 × 10?8 to 10?6 M. Up to 85% of this saturable binding is displaced by 10?5 M cytochalasin E (CE). This CE-sensitive binding also appears heterogeneous with KD similar to those of the overall binding. The CE-insensitive binding, however, appears as a single component with KD ≌ 4 × 10?7 M. The sedimentable constituents from frozen, thawed, and washed cells also bind CB with KD ranging from 2.4 × 10?8 to 1.5 × 10?6 M and a total capacity of approximately 39 p mols/mg protein which accounts for only 4% of the ligand binding to the intact cell. The major portion (60–80%) of this CB binding is displaceable by 500 mM D-glucose and has a KD of 1.5 × 10?6M, while only 10–15% is CE-sensitive with a KD of 2.4 ± 10?8 M. It is concluded that 95% of the saturable CB binding in platelets is associated with the cytosol of which 80–85% is sensitive to CE and that only 3% of the cellular binding is glucose sensitive, membrane-associated binding. If the CE-sensitive binding associated with the cytosol is entirely to actin, the stoichiometry of this binding is approximately one CB to 30 actin monomers, which is greater by an order of magnitude than that for CB binding to muscle actin. 相似文献
13.
Somatostatin binding to pituitary plasma membranes. 总被引:3,自引:0,他引:3
J W Leitner R M Rifkin A Maman K E Sussman 《Biochemical and biophysical research communications》1979,87(3):919-927
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
14.
D A Rigas C Eginitis-Rigas C Head 《Biochemical and biophysical research communications》1979,88(2):373-379
A new type of toxicity biphasically dependent on concentration was observed with diethyldithiocarbamate, a metal chelator utilized in medicine. As judged by cell survival and [3H]Urd incorporation, diethyldithiocarbamate was maximally toxic to T lymphocytes and polymorphonuclears at 2.5×10?5 M (first phase) and at higher than 2.5×10?3 M (second phase), but was not toxic at intermediate concentrations around 2.5×10?4 M. The response of chelator treated T lymphocytes to phytohemagglutinin was also biphasic. The first toxic phase was partially reversed by 2.5×10?5 M ZnCl2, while the second phase was partially reversed by 10?2 M CuCl2. This suggests that inhibition of Zn-metalloenzymes in the first phase and of Cu-metalloenzymes in the second may play a crucial role in the mechanism of toxicity. The second toxic phase may be in part due to the observed inhibition of superoxide dismutase rendering the cells susceptible to oxygen toxicity, like obligate anaerobes. 相似文献
15.
Abstract: Pridefine (AHR-1118) is a pyrrolidine derivative with clinically established antidepressant efficacy. Previous work from this laboratory indicates that pridefine is a reuptake blocker of catecholamines and serotonin with weak releasing activity. This study characterized the mode of amine uptake inhibition by pridefine as noncompetitive. The uptake experiments were performed utilizing ouabain instead of zero-degree controls to differentiate between the passive and active components of uptake. Furthermore, the passive component was resolved into diffusion and binding of substrate. Correction was made for the effects of ouabain on binding. Kinetic constants determined from Lineweaver-Burk plots were: Km= 3 × 10?7 M for NE, Km= 9 × 10?8 M for DA, and Km= 3 × 10?8 M for 5-HT. Dixon analyses of uptake at various pridefine concentrations indicated noncompetitive inhibition with Ki= 2.5 × 10?6 M for NE uptake, Ki= 2.0 × 10?6 M for DA uptake, and Ki= 1 × 10?5 M for 5-HT uptake. These constants compare well with IC50 values for the same transmitters: NE, IC50= 2.4 × 10?6 M; DA, IC50= 2.8 × 10?6 M; 5-HT, IC50= 1.0 × 10?5 M. The in vitro results indicate that pridefine is relatively specific as a catecholamine uptake blocker. It differs from tricyclic antidepressants which are reportedly competitive inhibitors of monoamine uptake. The possible mechanisms by which pridefine acts as a noncompetitive inhibitor are discussed. 相似文献
16.
Ch.V. Rao 《Prostaglandins & other lipid mediators》1973,4(4):567-576
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), PGF1α and PGF2α (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
17.
M.I. Schimerlik D.A. Malencik S.R. Anderson Y. Shalitin 《Biochemical and biophysical research communications》1982,106(4):1331-1339
Anthroylcholine was utilized as an extrinsic fluorescent probe in rapid kinetic studies of calcium dissociation from calmodulin (koff = 10 S?1) and the calmodulin-troponin I complex (koff = 6 S?1). At concentrations lower than 70 μM, the mechanism of dye binding agreed with the simple kinetic scheme in which the dye binds exclusively to the respective calcium complexes of calmodulin and calmodulin-troponin I. The sensitivity of anthroylcholine also made possible the estimation of values for the association (1.0 ± 0.8) × 108 S?1) and dissociation rate constants (2 ± 170 S?1) for troponin I binding to the calcium4-calmodulin complex. 相似文献
18.
S. Nicosia H.J. Crowley D. Oliva A.F. Welton 《Prostaglandins & other lipid mediators》1984,27(3):483-494
Leukotriene (LTC4) is one of the components of Slow Reacting Substance of Anaphylaxis (SRS-A) and is a potent constrictor of guinea pig ilea. The contraction is likely to be a receptor-mediated process. Here we report the existence of specific binding sites for 3H-LTC4 in a crude membrane preparation from guinea pig ileal longitudinal muscle.At 4°C in the presence of 20 mM Serine-borate, binding increases linearly with protein concentration, reaches equilibrium in 10 minutes, and is reversible upon addition of 3 × 10?5M unlabelled LTC4. The dissociation curve is consistent with the existence of more than one class of binding site. Ca++ and Mg++ greatly enhance the binding of 3H-LTC4 at equilibrium. In the presence of 5mM CaCl2 and MgCl2 not only LTC4 (IC50 10?7M), but also LTD4 (albeit with much lower affinity, IC50 = 6 × 10?5M) and the SRS-A antagonist FPL 55712 (IC50 = 10?5M) can compete with 3H-LTC4 for its binding sites. FPL 55712 only displaces 60–70% of the total amount bound, while LTC4 displaces 90–95%.These studies indicate that multiple classes of binding sites exist for 3H-LTC4 in guinea pig ileal longitudinal muscle, and that at least part of these binding sites might be related to the ability of LTC4 to contract guinea pig ilea. 相似文献
19.
We have studied the affinity of methylmalonyl CoA mutase for its required cofactor, adenosylcobalamin, in extracts of control and mutant human cultured fibroblasts. Control enzyme has an apparent Km for adenosylcobalamin of 6–7 × 10?8 M. Five mutant cell lines from patients with methylmalonicacidemia due to a mutase apoenzyme defect were studied. Three have undetectable mutase activity (<0.15% of control) at all cofactor concentrations. Two others, however, have markedly altered Km's for adenosylcobalamin of 2.8 × 10?4 M and 1.7 × 10?5 M. These mutant lines synthesize adenosylcobalamin normally and, by complementation analysis, are genetically identical to all other mutase apoenzyme mutants tested. We conclude that the mutase deficiency in these two cell lines results from structurally altered mutase apoenzymes with markedly reduced affinities for adenosylcobalamin. 相似文献
20.
4-oxo-N,N,N-trimethylpentanaminium chloride is a competitive inhibitor of eel acetylcholinesterase with KI = 8 × 10?6 M at 25°, 0.1 M NaCl, 0.04 M MgCl2, pH 7.5. Its binding decreases at low pH with pKa = 6.0. N,N,N-trimethylpentanaminium bromide has KI = 4 × 10?4 M under the same conditions. Its binding also decreases with pH with pKa = 5.35. Comparison with literature data indicates that the ketone binds much more strongly than substrates and that its binding shows the pH dependence expected for a transition state analog. 相似文献