共查询到20条相似文献,搜索用时 46 毫秒
1.
Héctor S. Barra Carlos E. Argaran˜a 《Biochemical and biophysical research communications》1982,108(2):654-657
Spermine, spermidine and putrescine produce dose dependent stimulation of the invitro tubulinyl-tyrosine carboxypeptidase. Maximal stimulation was obtained with spermine, spermidine or putrescine at 0.06 mM, 1 mM and 6 mM, respectively. At higher concentrations, the enzyme activity was inhibited. The enzyme was also activated by Mg++; the concentration formaximal effect was 4–6 mM. The stimulation produced by optimal concentration of each amine was unaffected by Mg++ up to 2 mM; higher concentration of Mg++ showed inhibitory effect. At optimal Mg++ concentration, the carboxypeptidase activity was inhibited by increasing amine concentration. The amines at 0.5 or 5 mM did not produce any effect on the incorporation of tyrosine catalyzed by tubulin tyrosine ligase. 相似文献
2.
Frederick L. Kiechle Halina Malinski Diane M. Dandurand Janet B. McGill 《Molecular and cellular biochemistry》1990,93(2):195-206
Summary The ability of polyamines and other cationic compounds including monoamines, amino acids, poly-L-arginine, poly-D-lysine and poly-L-lysine, to alter pyruvate dehydrogenase (PDH) activity in mitochondria from rat epididymal adipocytes was determined. PDH was assayed with the substrate [1-14C] pyruvate in the presence of 0.05 mM Ca2+ and Mg2+. Nine of the fourteen compounds tested at 0.1 mM caused a significant increase (procaine, 3-(-morpholinopropionyl) benzo[b]thiophene [VII], spermine, spermidine, putrescine, lysine and tryptophan) or decrease (poly-L-arginine, 3-(-piperidinopropionyl) benzo[b]thiophene) in PDH activity. None of these compounds nonenzymatically decarboxylated [1-14C] pyruvate to release 14CO2. NaF, a PDH phosphatase inhibitor, suppressed the stimulatory effects of those compounds tested: procaine, tryptophan, VII, spermine and spermidine. These results imply that these five compounds activate PDH activity through stimulation of the PDH phosphatase. When the Mg2+ concentration was increased from 0.05 to 4.5 mM, the stimulatory effect of spermine was increased, consistent with the finding by others that spermine lowers the Km of the enzyme for Mg2+. However, at Mg2+ concentrations greater than 0.3 mM, the stimulatory effect of VII was unaltered, procaine failed to alter PDH activity, lysine inhibited PDH activity, and poly-L-lysine stimulated PDH activity. Therefore, polyamines and other positively charged small molecules may be physiologic regulators of PDH activity. 相似文献
3.
Joseph D. Robinson 《Journal of bioenergetics and biomembranes》1980,12(3-4):165-174
The (Na+ + K+)-dependent ATPase exhibits substrate sites with both high affinity (K
m near 1 µM) and low affinity (K
m near 0.1 mM) for ATP. To permit the study of nucleotide binding to the high-affinity substrate sites of a canine kidney enzyme preparation in the presence as well as absence of MgCl2, the nonhydrolyzable - imido analog of ATP, AMP-PNP, was used in experiments performed at 0–4°C by a centrifugation technique. By this method theK
D for AMP-PNP was 4.2 µM in the absence of MgCl2. Adding 50 µM MgCl2, however, decreased theK
D to 2.2 µM; by contrast, higher concentrations of MgCl2 increased theK
D until, with 2 mM MgCl2, theK
D was 6 µM. The half-maximal effect of MgCl2 on increasing theK
D occurred at approximately 1 mM. This biphasic effect of MgCl2 is interpreted as Mg2+ in low concentrations favoring AMP-PNP binding through formation at the high-affinity substrate sites of a ternary enzyme-AMP-PNP-Mg complex; inhibition of nucleotide binding at higher MgCl2 concentrations would represent Mg2+ acting through the low-affinity substrate sites. NaCl in the absence of MgCl2 increased AMP-PNP binding, with a half-maximal effect near 0.3 mM; in the presence of MgCl2, however, NaCl increased theK
D for AMP-PNP. KCl decreased AMP-PNP binding in the presence or absence of MgCl2, but the simultaneous presence of a molar excess of NaCl abolished (or masked) the effect of KCl. ADP and ATP acted as competitors to the binding of AMP-PNP, although a substrate for the K+-dependent phosphatase reaction also catalyzed by this enzyme,p-nitrophenyl phosphate, did not. This lack of competition is consistent with formulations in which the phosphatase reaction is catalyzed at the low-affinity substrate sites. 相似文献
4.
Akerman KE 《Journal of bioenergetics and biomembranes》1977,9(2):141-149
The activation energy of mitochondrial Ca2+ transport has been studied in various conditions by Arrhenius plots in the temperature range 6–20°C. In the presence of Mg2+ the activation energy is decreased to 18 kJ/mole from that of 40 kJ/mole found in a sucrose medium. In the presence of the polyamine spermine the activation energy is practically 0 kJ/mole. A lanthanide Eu3+, which is a potent inhibitor of Ca2+ transport, has no significant effect on the activation energy. In a KCl medium the activation energy is increased to 70 kJ/mole. When both K+ and Mg+ are present the activation energy is nonlinear between 11 and 18°C. In the presence of K+ and spermine it is about 0 kJ/mole between 6 and 13°C and at higher temperatures 68 kJ/mole. Neither Mg2+ nor spermine affect the slope of the Arrhenius plot for state 4 respiration. Spermine decreases slightly the activation energy of Ca2+-stimulated respiration. Spermine also decreases the activation energy of valinomycin- or gramicidin-induced safranine uptake by liposomes from 68 to almost 0 kJ/mole between 17 and 30°C. The results indicate that Ca2+ binding to the polar head groups of the phospholipids at the membrane surface is the rate-limiting step of mitochondrial Ca2+ transport, because agents that inhibit Ca2+ binding to these sites (Mg2+, spermine, K+) have the most marked effect, whereas Eu3+, which, because of the small concentration used, ought to interact mainly with the mitochondrial Ca2+ transport system, has no significant effect on the temperature sensitivity of mitochondrial Ca2+ transport. 相似文献
5.
Garçon DP Lucena MN França JL McNamara JC Fontes CF Leone FA 《The Journal of membrane biology》2011,244(1):9-20
We investigated the effect of the exogenous polyamines spermine, spermidine and putrescine on modulation by ATP, K+, Na+, NH4
+ and Mg2+ and on inhibition by ouabain of posterior gill microsomal Na+,K+-ATPase activity in the blue crab, Callinectes ornatus, acclimated to a dilute medium (21‰ salinity). This is the first kinetic demonstration of competition between spermine and
spermidine for the cation sites of a crustacean Na+,K+-ATPase. Polyamine inhibition is enhanced at low cation concentrations: spermidine almost completely inhibited total ATPase
activity, while spermine inhibition attained 58%; putrescine had a negligible effect on Na+,K+-ATPase activity. Spermine and spermidine affected both V and K for ATP hydrolysis but did not affect ouabain-insensitive ATPase activity. ATP hydrolysis in the absence of spermine and
spermidine obeyed Michaelis–Menten behavior, in contrast to the cooperative kinetics seen for both polyamines. Modulation
of V and K by K+, Na+, NH4
+ and Mg2+ varied considerably in the presence of spermine and spermidine. These findings suggest that polyamine inhibition of Na+,K+-ATPase activity may be of physiological relevance to crustaceans that occupy habitats of variable salinity. 相似文献
6.
《Life sciences》1995,57(7):685-694
The metabolism of phosphoinositides plays an important role in the signal transduction pathways. We report here that naturally occuring polyamines affect the activities of phosphatidylinositol (PI) 3-kinase and PI 4-phosphate (PIP) 5-kinase differently. While polyamines inhibited the PI 3-kinase activity, they stimulated the activity of PIP 5-kinase in the order of spermine > spermidine > putrescine. Spermine inhibited the PI 3-kinase activity in a concentration-dependent manner with an IC50 of 100 μM. On the other hand, spermine (5 mH) stimulated the activity of PIP 5-kinase 2–3 fold. Kinetic studies of spermine-mediated inhibition of PI 3-kinase revealed that it was noncompetitive with respect to ATP. The effect of Mg2+ and PIP, concentration on kinase activity was sigmoidal, with spermine inhibiting PI 3-kinase activity at all PIP2 concentrations. While 1 mH calcium stimulated PI 3-kinase activity at submaximal concentrations of Mg2+ (1.25 mH), inhibition was observed at optimal concentration of Mg2+(2 mM). We propose that spermine may modulate the cellular signal by virtue of its differential effects on phosphoinositide kinases. 相似文献
7.
The characteristics and specific requirements for the formation of polyphenylalanine from Phe-[14C] in a barley ribosome cell-free incorporation system were detailed. The polyamines spermine, spermidine and putrescine, and the inorganic cations Ca2+, Ba2+ and Mn2+ demonstrated different capabilities for replacing the Mg2+ requirement in the incorporation system. Spermine was extremely efficient in this respect, followed by spermidine; all of the cations tested showed discrete concentration ranges of effectiveness. The data supported the suggestion that, at least to a certain extent, the cation requirement for protein syntheis may be non-specific. 相似文献
8.
Effects of Polyamines on the Oxidation of Exogenous NADH by Jerusalem Artichoke (Helianthus tuberosus) Mitochondria 总被引:1,自引:1,他引:0
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The effect of polyamines (putrescine, spermine, and spermidine) on the oxidation of exogenous NADH by Jerusalem artichoke (Helianthus tuberosus L. cv. OB1) mitochondria, have been studied. Addition of spermine and/or spermidine to a suspension of mitochondria in a low-cation medium (2 millimolar-K+) caused a decrease in the apparent Km and an increase in the apparent Vmax for the oxidation of exogenous NADH. These polycations released by screening effect the mitochondrially induced quenching of 9-aminoacridine fluorescence, their efficiency being dependent on the valency of the cation (C4+ > C3+). Conversely, putrescine only slightly affected both kinetic parameters of exogenous NADH oxidation and the number of fixed charges on the membranes. Spermine and spermidine, but not putrescine, decreased the apparent Km for Ca2+ from about 1 to about 0.2 micromolar, required to activate external NADH oxidation in a high-cation medium, containing physiological concentrations of Pi, Mg2+ and K+. The results are interpreted as evidence for a role of spermine and spermidine in the modulation of exogenous NADH oxidation by plant mitochondria in vivo. 相似文献
9.
Karl E. O. Åkerman 《Journal of bioenergetics and biomembranes》1977,9(1):65-72
Plots relating the initial rate of mitochondrial Ca2+ transport to the Ca2+ concentration (kinetic plots) have a hyperbolic shape in a Ca2+ concentration range of 2.5–100 µM as measured in sucrose or KCl media. In the presence of Mg2+ or a polyamine spermine, which both are competitive inhibitors of Ca2+ binding to low affinity sites at the membrane surface, the shape of the plots becomes sigmoidal. At higher concentrations of these agents linear kinetic plots are obtained as measured in a sucrose medium. In a KCl medium the sigmoidality of the kinetic plots is enhanced by an increase in the Mg2+ or spermine concentration. It is suggested that Mg2+ and spermine affect the kinetics of Ca2+ transport by interfering with Ca2+ binding to low affinity sites of the membrane surface and that the binding of Ca2+ to these sites is the first step of the mitochondrial Ca2+ transport. 相似文献
10.
Mauro Salvi 《生物化学与生物物理学报:生物膜》2004,1661(2):113-124
Mammalian mitochondria are able to enhance Ca2+ accumulation in the presence of polyamines by activating the saturable systems of Ca2+ inward transport and buffering extramitochondrial Ca2+ concentrations to levels similar to those in the cytosol of resting cells. This effect renders them responsive to regulate free Ca2+ concentrations in the physioloical range. The mechanism involved is due to a rise in the affinity of the Ca2+ transport system, induced by polyamines, most probably exhibiting allosteric behaviour. The regulatory site of this mechanism is the so-called S1 binding site of polyamines, which operates in physiological conditions and is located in the energy well between the two peaks present in the energy profile of mitochondrial spermine transport. Spermine is bidirectionally transported across teh inner membrane by cycling, in which influx and efflux are driven by electrical and pH gradients, respectively. Most probably, polyamine affects the Ca2+ transport system when it acts from the outside-that is, in the direction of its uniporter channel, in order to reach the S1 site. Important physiological functions are related to activation of Ca2+ transport systems by polyamines and their interactions with the S1 site. These functions include a rise in the metabolic rate for energy supply and modulation of mitochondrial permeability transition induction, with consequent effects on the triggering of the apoptotic pathway. 相似文献
11.
Calmodulin stimulation of calcium uptake and (Ca2+-Mg2+)-ATPase activities in microsomes from canine tracheal smooth muscle 总被引:2,自引:0,他引:2
The role of calmodulin in the regulation of microsomal 45Ca2+ transport in canine tracheal smooth muscle was studied. Calmodulin stimulated ATP-dependent 45Ca2+ uptake and (Ca2+Mg2+)-ATPase activities in microsomes treated with 0.5 mM EDTA and 0.5 mM EGTA. Oxalate also stimulated ATP-dependent 45Ca2+ uptake and (Ca2+Mg2+)-ATPase activities and the stimulation was additive to the effects of calmodulin. The (Ca2+Mg2+)-ATPase and ATP-dependent 45Ca2+ uptake activities are probably related as they exhibited similar [Ca2+]free- and [calmodulin]-dependencies. These results indicate that calmodulin may play a role in the control of the cytosolic [Ca2+]free in canine tracheal smooth muscle. 相似文献
12.
Mata A Marques D Martínez-Burgos MA Silveira J Marques J Mesquita MF Pariente JA Salido GM Singh J 《Molecular and cellular biochemistry》2008,307(1-2):193-207
This study investigated the effects of extracellular Mg2+ ([Mg2+]o) on basal and acetylcholine (ACh)-evoked amylase secretion and intracellular free Ca2+ ([Ca2+]i) in rat parotid acinar cells. In a medium containing 1.1 mM [Mg2+]o, ACh evoked significant increases in amylase secretion and [Ca2+]i. Either low (0 mM) or elevated (5 and 10 mM) [Mg2+]o attenuated ACh-evoked responses. In a nominally Ca2+ free medium, elevated [Mg2+]o attenuated basal and ACh-evoked amylase secretion and [Ca2+]i. In parotid acinar cells incubated with either 0, 1.1, 5 or 10 mM [Mg2+]o, ACh evoked a gradual decrease in [Mg2+]i. These results indicate that the ACh-evoked Mg2+ efflux is an active process since Mg2+ has to move against its gradient. Either lidocaine, amiloride, N-methyl-d-glucamine, quinidine, dinitrophenol or bumetanide can elevate [Mg2+]i above basal level. In the presence of these membrane transport inhibitors, ACh still evoked a decrease in [Mg2+]i but the response was less pronounced with either [Na+]o removal or in the presence of either amiloride or quinidine. These results indicate marked interactions between Ca2+ and Mg2+ signalling in parotid acinar cells and that ACh-evoked Mg2+ transport was not dependent upon [Na+]o. 相似文献
13.
Vacuolar membrane vesicles of Saccharomyces cerevisiae accumulated spermine and spermidine in the presence of ATP, not in the presence of ADP. Spermine and spermidine transport at pH 7.4 showed saturation kinetics with Km values of 0.2 mM and 0.7 mM, respectively. Spermine uptake was competitively inhibited by spermidine and putrescine, but was not affected by seven amino acids, substrates of active transport systems of vacuolar membrane. Spermine transport was inhibited by the H(+)-ATPase-specific inhibitors bafilomycin A1 and N,N'-dicyclohexylcarbodiimide, but not by vanadate. It was also sensitive to Cu2+ or Zn2+ ions, inhibitors of vacuolar H(+)-ATPase. Both 3,5-di-tert-butyl-4-hydroxybenzilidenemalononitrile (SF6847) and nigericin blocked completely the spermine uptake, but valinomycin did not. [14C]Spermine accumulated in the vesicles was exchangeable with unlabeled spermine and spermidine. However, it was released by a protonophore only in the presence of a counterion such as Ca2+. These results indicate that a polyamine-specific transport system depending on a proton potential functions in the vacuolar membrane of this organism. 相似文献
14.
The thermodynamic efficiency of the calmodulin-activated form of the Ca2+-pumping ATPase of the bovine cardiac sarcolemma (SL) was evaluated in sealed vesicles under reversible conditions. The free internal Ca2+ concentration ([Ca2+]i) established in the SL vesicle lumen by action of the ATPase was determined as a function of the [ATP]/([ADP][Pi]) ratio for the following experimental conditions: 250mM sucrose, 100mM KCI, 0.1mM Mg2+, 25mM HEPES, 25mM Tris, pH 7.40, at 37°C, [Ca2+]o=50nM (1mM Ca/EGTA buffer), 0.75mM Mg-ATP, 0.1mM Pi, variable [ADP]. Under these conditions, with the pump working near itsK
m
of 64nM, the [Ca2+]i achieved was 18mM, decreasing with increasing [ADP] for [ADP] 0.84mM. A plot of the square of the [Ca2+]i/[Ca2+]o ratio against [ATP]/([ADP][Pi]) gave a straight line with a slope of 1.5×107M. This was in agreement, within the experimental error, with the equilibrium constant for ATP hydrolysis under these conditions (1.09×107M). These results demonstrate (1) tight coupling between Ca2+ transport and ATP hydrolysis with a stoichiometry of 2 Ca2+ moved per ATP split and (2) a low degree of passive leakage. Analysis at low [ADP] (<0.83mM) showed the unexpected result that ADP increases the rate of theforward reaction of the pump. The maximal effect on the initial rate is a 96±5% increase, with an EC50 of approximately 0.4mM (ADP). Similar but lesser stimulation was observed with CDP. The implications of the above results for the energetics of the pump and for its physiological function in the beating heart are discussed. 相似文献
15.
Muhammad Akbar Anjum 《Acta Physiologiae Plantarum》2010,32(5):951-959
Six-month-old, uniform-sized seedlings of Cleopatra mandarin growing in hydroponics in Hoagland nutrient solution under glasshouse
conditions were subjected to salinity treatment (NaCl 75 mM). Addition of NaCl to the nutrient medium reduced plant growth
(shoot height and leaf number), leaf chlorophyll content, chlorophyll fluorescence yields (Fv/Fm), net photosynthesis, stomatal
conductance, transpiration rate, intracellular CO2 concentration, N, K+ and Ca2+ + Mg2+ contents of the leaves; and increased total putrescine (Put), proline and Na+ and Cl− contents of the leaves. Addition of d-arginine (1 mM) to the saline medium further reduced the values of all the parameters except Fv/Fm, photosynthesis and related
parameters and Ca2+ + Mg2+ contents of the leaves, and increased total spermine (Spm) content of the leaves. However, total Put contents were decreased;
spermidine (Spd) contents and Na+ and Cl− titres of the leaves were unaffected. Weekly spray of d-arginine (5 mM) was less harmful than its addition to the nutrient medium (1 mM). Addition of 0.5 mM Spd to the medium alleviated
the adverse effects of d-arginine by improving plant growth, leaf chlorophyll content, total Put, Spd, Spm, N, P, K+ and Ca2+ + Mg2+ contents of the leaves. Weekly spray of Spd (5 mM) was less effective than its addition in the nutrient medium (0.5 mM). 相似文献
16.
D Konecki G Kramer P Pinphanichakarn B Hardesty 《Archives of biochemistry and biophysics》1975,169(1):192-198
The salt wash fraction removed from rabbit reticulocyte ribosomes with 0.5 m KCl contains dialyzable components required for maximum in vitro synthesis of globin peptides. The active substances were identified as spermidine and spermine. Rabbit reticulocyte ribosomes contain spermine and spermidine in a 1:3 ratio of which about 75% is removed in the 0.5 m KCl wash fraction. Dialyzed salt wash can be reactivated for in vitro protein synthesis by addition of either spermine, spermidine, or Mg2+ ion. A twofold higher leucine incorporation into protein was obtained with the optimum concentration of either polyamine than with Mg2+. Spermidine is effective in lowering the Mg2+ requirement for initiation of phenylalanine peptides in the poly(U)-directed system, apparently by formation of an initiation complex. Also, spermidine competitively interferes with edeine inhibition of globin chain initiation. These results indicate that spermidine may play a special role in peptide initiation. 相似文献
17.
The effects of extracellular Mg2+ on both dynamic changes of [Ca2+]i and apoptosis rate were analysed. The consequences of spatial and temporal dynamic changes of intracellular Ca2+ on apoptosis, in thapsigargin- and the calcium-ionophore 4BrA23187-treated MCF7 cells were first determined. Both 4BrA23187 and thapsigargin induced an instant increase of intracellular Ca2+ concentrations ([Ca2+]i) which remained quite elevated (> 150 nM) and lasted for several hours. [Ca2+]i increases were equivalent in the cytosol and the nucleus. The treatments that induced apoptosis in MCF7 cells were systematically associated with high and sustained [Ca2+]i (150 nM) for several hours. The initial [Ca2+]i increase was not determinant in the events triggering apoptosis. Thapsigargin-mediated apoptosis and [Ca2+]i rise were abrogated when cells were pretreated with the calcium chelator BAPTA. The role of the extracellular Mg2+ concentration has been studied in thapsigargin treated cells. High (10 mM) extracellular Mg2+, caused an increase in basal [Mg2+]i from 0.8 ± 0.3 to 1.6 ± 0.5 mM. As compared to 1.4 mM extracellular Mg2+, 1 M thapsigargin induces, in 10 mM Mg2+, a reduced percentage from 22 to 11% of fragmented nuclei, a lower sustained [Ca2+]i and a lower Ca2+ influx through the plasma membrane. In conclusion, the cell death induced by thapsigargin was dependent on high and sustained [Ca2+]i which was inhibited by high extracellular and intracellular Mg2+. 相似文献
18.
Kazuei Igarashi Kazuo Kishida Seiyu Hirose 《Biochemical and biophysical research communications》1980,96(2):678-684
Effect of polyamines on the methylation of adenine in 16S rRNA was examined using the purified methylating enzyme. When 23S core particles were used as substrate, the activity was stimulated by Mg2+, Ca2+ and monovalent cations. Even in the presence of optimal concentrations of Mg2+ and NH4+, the addition of 1 mM spermidine stimulated the methylation approximately 1.7-fold. When 30S ribosomal subunits were used as substrate, the rate of methylation was 20% of that of the methylation of 23S core particles. The activity was not influenced significantly by Mg2+, Ca2+ or monovalent cations. The addition of spermidine inhibited the methylation. 相似文献
19.
Dagmar Siliprandi A. Toninello F. Zoccarato Michela Rugolo N. iliprandi 《Journal of bioenergetics and biomembranes》1978,10(1-2):1-11
Addition to rat liver mitochondria of 2 mM inorganic phosphate or 0.15 mM diamide, a thiol-oxidizing agent, induced an efflux of endogenous Mg2+ linear with time and dependent on coupled respiration. No net Ca2+ release occurred under these conditions, while a concomitant release of K+ was observed. Mg2+ efflux mediated either by Pi or low concentrations of diamide was completely prevented by EGTA, Ruthenium red, and NEM. These reagents also inhibited the increased rate of state 4 respiration induced both by Pi and diamide. At higher concentrations (0.4 mM), diamide induced an efflux of Mg2+ which was associated also with a release of endogenous Ca2+. Under these conditions EGTA completely prevented Mg2+ and K+ effluxes, while they were only partially inhibited by Ruthenium red and NEM. It is assumed that Mg2+ efflux, occurring at low diamide concentrations or in the presence of phosphate, is dependent on a cyclic in-and-out movement of Ca2+ across the inner mitochondrial membrane, in which the passive efflux is compensated by a continuous energy linked reuptake. This explains the dependence of Mg2+ efflux on coupled respiration, as well as the increased rate of state 4 respiration. The dependence of Mg2+ efflux on phosphate transport is explained by the phosphate requirement for Ca2+ movement.Abbreviations Diamide
diazenedicarboxylic acidbis-dimethylamide
- FCCP
p-trifluoromethoxyphenylhydrazone
- EGTA
ethylene glycol-bis-(2-amino ethyl ether)-N,N-tetracetic acid
- Pi
inorganic phosphate
- Ruthenium red
Ru2(OH)2Cl4 · 7NH3 · 3H2O
- state 4
controlled state of respiration in the presence of substrate
- RCI
respiratory control index
- NEM
N-ethyl maleimide
A partial and preliminary report of these results has been published inBiochem. Biophys. Res. Comm.,78 (1977) 23. 相似文献
20.
Ian J. Reynolds 《Journal of neurochemistry》1994,62(1):54-62
Abstract: This study investigated the binding of [3H] CGP 39653, a novel high-affinity antagonist of the N-methyl-D- aspartate (NMDA) recognition site of the NMDA receptor complex. [3H] CGP 39653 bound to the NMDA receptor in well washed rat brain membranes with an affinity of about 15 nM. Other NMDA site drugs inhibited [3H] CGP 39653 binding with the following order of potency: DL-(tetrazol-5- yl)glycine > glutamate > CGS 19755 > DL-2-amino-5- phosphonovalerate (DL-AP5) > NMDA. Glycine and 5, 7- dichlorokynurenate partially inhibited binding. The poly-amines spermine and spermidine increased [3H] CGP 39653 binding (EC50 values of 10 and 22 μM, respectively). This effect was mimicked by arcaine, 1, 5-diethylaminopiperidine, diaminodecane, diethylenetriamine, and Mg2+. The increase in [3H] CGP 39653 was a result of an increased affinity of the binding site for the ligand with very little effect on binding site density. Spermine and Mg2+also increased the affinity of the antagonists DL-AP5 and CGS 19755, but had only minor effects on the affinity of glutamate and NMDA. Arcaine did not reverse the enhancement of [3H] CGP 39653 binding by spermine, spermidine, or Mg2+. Channel-blocking dissociative anesthetics, including dizocilpine and ketamine, did not alter basal or Mg2+-stimulated [3H] CGP 39653 binding. Spermine did not alter either the enhancement of [3H]- dizocilpine by glutamate or the inhibition of [3H]dizocilpine by DL-AP5 or CGS 19755. These studies show that poly-amines and divalent cations selectively enhance the affinity of antagonists for the agonist binding site on the NMDA receptor complex. However, this effect is mediated by a site independent of the primary polyamine site defined using [3H] dizocilpine binding. 相似文献