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1.
Choline oxidase catalyzes the oxidation of choline to glycine-betaine, with betaine-aldehyde as intermediate and molecular oxygen as primary electron acceptor. This study reports on the inhibitory effects of triarylmethanes (cationic malachite green; neutral leukomalachite green), phenoxazines (cationic, meldola blue and nile blue; neutral nile red) and a structurally-related phenothiazine (methylene blue) on choline oxidase, assayed at 25 degrees C in 50 mM MOPS buffer, pH 7, using choline as substrate. Methylene B acted as a competitive inhibitor with K(i) = 74 +/- 7.2 microM, pointing to the choline-binding site of the enzyme as a target site. Nile B caused noncompetitive inhibition of enzyme activity with K(i) = 20 +/- 4.5 microM. In contrast to methylene B and nile B, malachite G and meldola B caused complex, nonlinear inhibition of choline oxidase, with estimated K(i) values in the micromolar range. The difference in kinetic pattern was ascribed to the differential ability of the dyes to interact (and interfere) with the flavin cofactor, generating different perturbations in the steady-state balance of the catalytic process.  相似文献   

2.
The kinetic effects of a selection of triarylmethane, phenoxazine and phenothiazine dyes (pararosaniline (PR), malachite green (MG), methyl green (MeG); meldola blue (MB), nile blue (NB), nile red (NR); methylene blue (MethB)) and of ethopropazine on horse serum butyrylcholinesterase were studied spectrophotometrically at 25 °C in 50 mM MOPS buffer, pH 8, using butyrylthiocholine as substrate. PR, MeG, MB and ethopropazine acted as linear mixed type inhibitors of the enzyme, with respective Ki values of 4.5 ± 0.50 μM, 0.41 ± 0.007 μM, 0.44 ± 0.086 μM and 0.050 ± 0.0074 μM. MG, NB, MethB and NR caused complex, nonlinear inhibition pointing to cooperative binding at two sites. Intrinsic K′ values (≡[I]20.5 extrapolated to [S]=0) for MG, NB, NR and MethB were 0.20 ± 0.096 μM, 0.0018 ± 0.0015 μM, 0.92 ± 0.23 μM and 0.23 ± 0.08 μM. NB stood out as a potent inhibitor effective at nM levels. Comparison of inhibitory effects on horse and human serum butyrylcholinesterases suggested that the two enzymes must have distinct microstructural features.  相似文献   

3.
Blood-brain barrier (BBB) transport of choline and certain choline analogs was studied in adult and suckling rats, and additionally compared in the paleocortex and neocortex of adult rats. Saturable uptake was characterized by a single kinetic system in all cases examined, and in adult rat forebrains we determined a Km= 442 ± 60 μM and Vmax= 10.0 ± 0.6 nmol min-1 g-1. In 14–15-day-old suckling forebrains a similar Km (= 404 ± 88 μM) but higher Vmax (= 12.5 ± 1.5 nmol min-1 g-1) was determined. When choline uptake was compared in two regions of the forebrain, similar Michaelis-Menten constants were determined but a higher uptake velocity was found in the neocortex (i.e. neocortex Km= 310 ± 103 μM and Vmax= 12.6 ± 2.8 nmol min-1g-1; paleocortex Km= 217 ± 76 μM and Vmax= 7.2 ± 1.5 nmol min-1 g-1). Administration of radiolabelled choline at low (5 μM) and high (100 μM) concentrations, followed by microwave fixation 60 s later and chloroform-methanol-water separations of the homogenized brain did not suggest a relationship between concentration and the appearance of label in lipid or aqueous fractions as observed in another in-vitro study elaborating two-component kinetics of choline uptake. It was observed that 60s after carotid injection 12–14% of the radiolabel in the ipsilateral cortex was found in the chloroform-soluble fraction. Hemicholinium-3 (Ki= 111 μM), dimethylaminoethanol (Ki= 42 μM), tetraethyl ammonium chloride, tetramethyl ammonium chloride, 2-hydroxyethyl triethylammonium iodide, carnitine, normal rat serum, and to a lesser extent lithium and spermidine all inhibited choline uptake in the BBB. Unsubstituted ammonium chloride and imipramine did not inhibit choline uptake. No difference was observed in blood-brain barrier choline uptake of unanesthetised, carotid artery-catheterized animals, and comparable sodium pentobarbital-anesthetized controls.  相似文献   

4.
A sarcosine dehydrogenase was purified to homogeneity from cell free extract of Pseudomonas putida aerobically grown in a medium containing creatinine or betaine as the carbon and nitrogen sources. The enzyme catalyzed dehydrogenation of N-methyl derivatives of some amino acids but was inert toward dimethylglycine, betaine and choline. Phenazine methosulfate, 2, 6-dichlorophenol indophenol, methylene blue, meldora blue, nile blue and potassium ferricyanide served as electron carriers. The maximal activity was observed at pH 8.0–9.0. The Km and Kmax values for sarcosine were 29 mm and 1.2 μmol/min/mg, respectively. The molecular weight was estimated to be about 170,000, presumably composed of four sub-units. Spectrophotometric and fluorometric analyses indicated that the enzyme was a flavoprotein.  相似文献   

5.
A series of new monophosphates of 1-[2-(phosphonomethoxy)alkyl]thymines, such as PMPTp, 3-MeO-PMPTp, HPMPTp, and FPMPTp, were synthesized and tested for their ability to inhibit human thymidine phosphorylase. Kinetic measurements of enzyme activity were performed using thymidine and inorganic phosphate as the substrates. The data show that some monophosphates provide a considerable increase of the multisubstrate inhibitory effect. The highest inhibitory potency was found with (R)-FPMPTp 4c (K i dT = 4.09 ± 0.47 μM, K i(Pi) = 2.13 ± 0.29 μM) and (R) 3-MeO-PMPTp 4d (K i dT = 5.78 ± 0.71 μM, K i(Pi) = 2.71 ± 0.37 μM).  相似文献   

6.
Abstract: We have cloned and expressed a rat brain cDNA, TS11, that encodes a μ-opioid receptor based on pharmacological, physiological, and anatomical criteria. Membranes were prepared from COS-7 cells transiently expressing TS11 bound [3H]diprenorphine with high affinity (KD = 0.23 ± 0.04 nM). The rank order potency of drugs competing with [3H]diprenorphine was as follows: levorphanol (Ki = 0.6 ± 0.2 nM) ≈β-endorphin (Ki = 0.7 ± 0.5 nM) ≈ morphine (Ki = 0.8 ± 0.5 nM) ≈ [d -Ala2, N-Me-Phe4,Gly-ol5]-enkephalin (DAMGO; Ki = 1.6 ± 0.5 nM) ? U50,488 (Ki = 910 ± 0.78 nM) > [d -Pen2,5]-enkephalin (Ki = 3,170 ± 98 nM) > dextrorphan (Ki = 4,100 ± 68 nM). The rank order potencies of these ligands, the stereospecificity of levorphanol, and morphine's subnanomolar Ki are consistent with a μ-opioid binding site. Two additional experiments provided evidence that this opioid-binding site is functionally coupled to G proteins: (a) In COS-7 cells 50 µM 5′-guanylylimidodiphosphate shifted a fraction of receptors with high affinity for DAMGO (IC50 = 3.4 ± 0.5 nM) to a lower-affinity state (IC50 = 89.0 ± 19.0 nM), and (b) exposure of Chinese hamster ovary cells stably expressing the cloned μ-opioid receptor to DAMGO resulted in a dose-dependent, naloxone-sensitive inhibition of forskolin-stimulated cyclic AMP production. The distribution of mRNA corresponding to the μ-opioid receptor encoded by TS11 was determined by in situ hybridization to brain sections prepared from adult female rats. The highest levels of μ-receptor mRNA were detected in the thalamus, medial habenula, and the caudate putamen; however, significant hybridization was also observed in many other brain regions, including the hypothalamus.  相似文献   

7.
A series of vinyl functionalized 5,6-dimethylbenzimidazolium salts are synthesized. All compounds were fully characterized by elemental analyses, MS, 1H-NMR, 13C-NMR, and IR spectroscopy techniques. Enzyme inhibition is a very active area of research in drug design and development. In this study, the synthesized novel benzimidazolium salts were evaluated toward the human erythrocyte carbonic anhydrase I (hCA I), and II (hCA II) isoenzymes, acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) enzymes. They demonstrated highly potent inhibition ability against hCA I with Ki values of 484.8 ± 62.6–1389.7 ± 243.2 nM, hCA II with Ki values of 298.9 ± 55.7–926.1 ± 330.0 nM, α-glycosidase with Ki values of 170.3 ± 27–760.1 ± 269 μM, AChE with Ki values of 27.1 ± 3–77.6 ± 1.7 nM, and BChE with Ki values of 21.0 ± 5–61.3 ± 15 nM. As a result, novel vinyl functionalized 5,6-dimethylbenzimidazolium salts (1a–g) exhibited effective inhibition profiles toward studied metabolic enzymes. Therefore, we believe that these results may contribute to the development of new drugs particularly to treat some global disorders including glaucoma, Alzheimer's disease, and diabetes.  相似文献   

8.
The cystic fibrosis transmembrane conductance regulator (CFTR) protein contains a canonical ATP-binding cassette (ABC) signature motif, LSGGQ, in nucleotide binding domain 1 (NBD1) and a degenerate LSHGH in NBD2. Here, we studied the contribution of the conserved residues G551 and G1349 to the pharmacological modulation of CFTR chloride channels by phloxine B using iodide efflux and whole-cell patch clamp experiments performed on the following green fluorescent protein (GFP)-tagged CFTR: wild-type, delF508, G551D, G1349D, and G551D/G1349D double mutant. We found that phloxine B stimulates and inhibits channel activity of wild-type CFTR (Ks = 3.2 ± 1.6 μM, Ki = 38 ± 1.4 μM) and delF508 CFTR (Ks = 3 ± 1.8 μM, Ki = 33 ± 1 μM). However, CFTR channels with the LSGDQ mutated motif (mutation G551D) are activated (Ks = 2 ± 1.13 μM) but not inhibited by phloxine B. Conversely, CFTR channels with the LSHDH mutated motif (mutation G1349D) are inhibited (Ki = 40 ± 1.01 μM) but not activated by phloxine B. Finally, the double mutant G551D/G1349D CFTR failed to respond not only to phloxine B stimulation but also to phloxine B inhibition, confirming the importance of both amino acid locations. Similar results were obtained with genistein, and kinetic parameters were determined to compare the pharmacological effects of both agents. These data show that G551 and G1349 control the inhibition and activation of CFTR by these agents, suggesting functional nonequivalence of the signature motifs of NBD in the ABC transporter CFTR.  相似文献   

9.
Adenine uptake into human blood platelets is a carrier-mediated process with a Km of 159±21 nM and a V of 100±10 pmoles/min per 109 platelets (in citrated platelet-rich plasma). The Q10 was 2.53±0.22. A pH optimum was found at 7.5. Washing of the platelets increased the Km to 453±33 nM and V to 397±38 pmoles/min per 109 platelets. The change in shape induced in platelets by ADP was accompanied by an increase in V (2 times) and Km (1.5 times).Guanine (Ki 50 μM), hypoxanthine (Ki 390 μM), adenine-N′-oxide (Ki 40 μM), adenosine (Ki 100 μM), RA 233 (Ki 75 μM) and papaverine (Ki 15 μM) acted as competitive inhibitors. Adenosine at low concentrations, and prostaglandin E1 gave inhibition at only high adenine levels. A similar inhibition was obtained with 2-deoxy-d-glucose. Sulfhydryl-group inhibitors, pyrimidines and ouabain had no effect.  相似文献   

10.
Epileptic foci are associated with locally reduced taurine (2-aminoethanesulfonic acid) concentration and Na+, K+-ATPase (EC 3.6.1.3) specific activity. Topically applied and intraperitoneally administered taurine can prevent the development and/or spread of foci in many animal models. Taurine has been implicated as a possible cytosolic modulator of monovalent ion distribution, cytosolic “free” calcium activity, and neuronal excitability. Taurine may act in part by modulating Na+, K+-ATPase activity of neuronal and glial cells. We characterized the requirements for in vitro modulation of Na+, K+-ATPase by taurine. Normal whole brain homogenate Na+, K+-ATPase activity is 5.1 ± 0.4 (4) μmol Pi± h?1± mg?1 Lowry protein. Partial purification of the plasma membrane fraction to remove cytosolic proteins and extrinsic proteins and to uncouple cholinergic receptors yields a membrane-bound Na+, K+-ATPase activity of 204.6 ± 5.8 (4) mol Pi± h?1± mg?1 Lowry protein. Taurine activates the Na+, K+-ATPase at all levels of purification. The concentration dependence of activation follows normal saturation kinetics (K1/2= 39 mM taurine, activation maximum =+87%). The activation exhibits chemical specificity among the taurine analogues and metabolites: taurine = isethionic acid > hypotaurine > no activation =β-alanine = methionine = choline = leucine. Taurine can act as an endogenous activator/modulator of Na+, K+-ATPase. Its action is mediated by a membrane-bound protein.  相似文献   

11.
Abstract

We have shown that binding of 3H-dihydroalprenolol ([3H] DHA) to DDT1 MF-2 cells and cell membranes was of high affinity, saturable, stereoselective and reversible. The [3H]DHA dissociation constants were 0.63 ± 0.15 nM (n=6) and 0.83 ± 0.04 nM (n=5) for intact cells and cell membranes, respectively, with a binding site concentration for cells of 27,300 ± 5,200 sites/ cell (n=6) and for membranes 468 ± 24 fmoles/mg protein (n=5). The order of agonist competition for the [3H]-DHA binding site of DDT1 cell membranes was isoproterenol (Ki = 0.20 ± 0.07 μM) > epinephrine (Ki = 0.4 ± 0.2 μM) > norepinephrine (Ki = 66.5 ± 5.15 μM) consistent with a β2-selective receptor interaction. Zinterol, a β2-selective antagonist, (Ki = 0.05 ± 0.01 μM) was 18x more effective than metoprolol, a β1-selective antagonist (Ki = 0.9 ± 0.1 μM), in competing for the DHA binding site. A nonlinear iterative curve fitting analysis of zinterol and metoprolol binding isotherms indicated that (p>0.05) DDT1 cells possess a pure population of β2-adrenergic receptors. Finally, we have shown that DDT1 MF-2 cell β2-adrenergic receptor is functionally coupled to adenylate cyclase via a G/F protein complex as demonstrated in part by a guanine nucleotide requirement for isoproterenol stimulation of adenylate cyclase activity. In addition, guanine nucleotide mediated a reduction in the affinities of isoproterenol and epinephrine for the [3H]DHA binding site.  相似文献   

12.
Abstract: A series of choline analogues and nitrogen mustard derivatives were evaluated as inhibitors of high-affinity transport of choline in rat forebrain synaptosomes. When synaptosomes were preincubated for 10 min with choline mustard aziridinium ion, monoethylcholine and monoethylcholine mustard aziridinium ion, the agents appeared to be equipotent as inhibitors of high-affinity uptake (Ki=2.63, 3.15 and 2.72 μm , respectively). Acetylcholine mustard aziridinium ion was less potent than these compounds (Ki= 27.8 μm ), but it was more potent than ethoxycholine and ethoxycholine mustard aziridinium ion (Ki= 500 and 403 μm ) as a blocker of choline transport. From study with these compounds it was concluded that the high-affinity choline transport mechanism shows specificity for hydroxylated compounds over those in which the same hydroxyl has been acetylated (10-fold) and that the carbonyl oxygen of the acetylated analogues is important, as its removal (to form the ethylether derivative) decreased affinity another 20-fold. The presence of an aziridinium ring on the quaternary nitrogen in place of two methyl groups did not affect the blocking of transport at 10 min of inhibitor preincubation and replacement of a methyl group on the nitrogen by an ethyl group did not alter affinity for the high-affinity carrier. The aziridinium ring on the nitrogen of the mustard analogues was important, however, in determining the extent of reversibility of the binding of these agents to the carrier protein. Choline transport was not restored by washing synaptosomes that were incubated with choline mustard aziridinium ion or monoethylcholine mustard aziridinium ion, but was readily obtained in washed synaptosomes preincubated with monoethylcholine, hemicholinium-3, or pyrrolcholine. The results indicate that the mustard analogues may be potent alkylators of the high-affinity choline carrier and thus, useful agents in monitoring acetylcholine turnover in systems where the carrier is blocked.  相似文献   

13.
Abstract: Histamine N-methyltransferase (EC 2.1.1.8) was purified 4400–fold in 12% yield from guinea pig brain. The basic steps in the purification included differential centrifugation, calcium phosphate adsorption, DEAE-cel-lulose chromatography, and affinity chromatography on an S-adenosylhomocysteine-agarose matrix. The resulting protein was homogeneous by gel electrophoresis and was stable for at least 3 months at 80°C. It had an apparent molecular weight of 29 ,000 ± 1000 as determined by both gel filtration through Sephadex G-100 and by electrophoresis in sodium dodecyl sulfate-polyacrylamide gels. The isoelectric point of the protein was found to be 5.3. The pH optima for methylation of histamine were determined to be 7.5 and 9.0; the Kms for histamine and S-adenosyl-l-methionine were 13.57 ± 0.74 μM and 6.1 ± 0.12 μM, respectively; the Ki for S-adenosyl-l-homocysteine was 24.5 ± 1.45 μM.  相似文献   

14.
Histamine and polyamines have been implicated in the mediation of cell proliferation. Our previous work linked the growth-modulatory effects of histamine with its binding to intracellular sites in microsomes and nuclei of various tissues. In this study, we identify cytochrome P450 enzymes as a major component of microsomal intracellular sites in hepatocytes and demonstrate that polyamines compete with high affinity for histamine binding to them. Spectral measurement of histamine binding to P450 in liver microsomes resolved high and intermediate affinity binding sites (Ks1 = 2.4 ± 1.6 μM; Ks2 = 90 ± 17 μM) that corresponded to microsomal binding sites (Kd1 = 1.0 ± 0.9 μM; Kd2 = 57 ± 13 μM) resolved by 3H-histamine binding; additional low affinity (Kd3 ∼ 3 mM), and probably physiologically irrelevant, sites were resolved only by 3H-histamine radioligand studies. As determined spectrally, treatment of microsomes with NADPH/carbon monoxide decreased histamine binding to P450 by about 90% and, as determined by 3H-histamine binding, abolished the high affinity sites and reduced by 85% the number of intermediate sites. Spermine competed potently for 3H-histamine binding: in microsomes, Ki = 9.8 ± 5.8 μM; in nuclei, Ki = 13.7 ± 3.1 μM; in chromatin, Ki = 46 ± 33 nM. Polyamines inhibited the P450/histamine absorbance complex with the rank order of potency: spermine > spermidine ≫ putrescine. In contrast, histamine did not compete for 3H- spermidine binding in nuclei or microsomes, suggesting that polyamines modulate histamine binding allosterically. We propose that certain P450 isozymes that modulate gene function by controlling the level of oxygenated lipids, represent at least one common intracellular target of growth-regulatory endogenous bioamines and, as shown previously, of exogenous growth-modulatory drugs including antiestrogens, antiandrogens, and certain antidepressants and antihistamines. J. Cell. Biochem. 69:233–243, 1998. © 1998 Wiley-Liss, Inc.  相似文献   

15.
The reaction between glucose and methylene blue, catalyzed by glucose oxidase (GOD)was analysed calorimetrically. The amount of heat produced under saturating methylene blue concentrations ( > 10?2 mol/1)was measured with glucose concentration and time as parameters (kinetic procedure) Kinetic constants (pseudo one substrate kinetics) were derived from the experimental data: KM(glucose)= 1.18 × 10?3 mol/l and Vmax = 0.085 J/mg GOD min (3.89 · 10?6 mol/mg GOD min) Comparison of caloric with optical measurements gave an enthalpy of reaction of 22.52 kJ/mol. Considering the observed substrate inhibition, glucose determinations are possible up to glucose concentrations of 0.1 mol/l.  相似文献   

16.
The specific activity of dihydroorotate dehydrogenase, catalysing the conversion of l-5,6-dihydroorotate (l-DHO) to orotate, in Leishmania mexicana mexicana was found to be 22.1 ± 3.5 nmole/hr/mg protein in the amastigote, and 28.7 ± 4.6 nmole/hr/mg protein in the promastigote. The enzyme was found to be soluble and to require molecular O2 for activity in both forms of the parasite. Oxygen utilisation was not mediated through the mitochondrial cytochrome-containing respiratory chain, and phenazine methosulphate and ferricyanide could be used as electron acceptors by the enzyme in both aerobic and anaerobic conditions. The enzyme from both amastigote and promastigote had a pH optimum of 7.0, and the Km values for l-DHO were 11.8 ± 4.9 and 2.3 ± 0.4 μM, respectively. The pyrimidine analogs 5-methylorotate (Ki = 8.8 μM) and 5-aminoorotate (Ki = 57 μM) were shown to be competitive inhibitors of the promastigote enzyme, as was the reaction product orotate (Ki = 10 μM).  相似文献   

17.
Growth and pigment concentrations of the, estuarine dinoflagellate, Prorocentrum mariae-lebouriae (Parke and Ballantine) comb. nov., were measured in cultures grown in white, blue, green and red radiation at three different irradiances. White irradiances (400–800 nm) were 13.4, 4.0 and 1.8 W · m?2 with photon flux densities of 58.7 ± 3.5, 17.4 ± 0.6 and 7.8 ± 0.3 μM quanta · m?2· s?1, respectively. All other spectral qualities had the same photon flux densities. Concentrations of chlorophyll a and chlorophyll c were inversely related to irradiance. A decrease of 7- to 8-fold in photon flux density resulted in a 2-fold increase in chlorophyll a and c and a 1.6- to 2.4-fold increase in both peridinin and total carotenoid concentrations. Cells grown in green light contained 22 to 32% more peridinin per cell and exhibited 10 to 16% higher peridinin to chlorophyll a ratios than cells grown in white light. Growth decreased as a function of irradiance in white, green and red light grown cells but was the same at all blue light irradiances. Maximum growth rates occurred at 8 μM quanta · m?2· s?1 in blue light, while in red and white light maximum growth rates occurred at considerably higher photon flux densities (24 to 32 μM quanta · m?2· s?1). The fastest growth rates occurred in blue and red radiation. White radiation producing maximum growth was only as effective as red and blue light when the photon flux density in either the red or blue portion of the white light spectrum was equivalent to that of a red or of blue light treatment which produced maximum growth rates. These differences in growth and pigmentation indicate that P. mariae-lebouriae responds to the spectral quality under which it is grown.  相似文献   

18.
Designing small molecule inhibitors targeting cholinesterases (ChEs) is considered as an efficient strategy for the treatment of Alzheimer′s disease (AD). In the present study, based on a shaped-based pharmacophore (SBP) model that we reported previously, virtual screening was performed on four commercial compound databases, from which eight small molecules containing new structurally scaffolds were retained and evaluated. In general, six of these potential hits were identified to be selective ChEs inhibitors. Three compounds exhibited IC50 values and Ki values in micromolar range on acetylcholinesterase (AChE), the most active compound 4 showed IC50 value of 6.31 ± 2.68 μM and Ki value of 4.76 μM. Other three compounds displayed IC50 values and Ki values in micromolar range on butyrylcholinesterase (BChE) with high target selectivity, the most active compound 1 showed IC50 value of 3.87 ± 2.48 μM and Ki value of 1.52 μM. Multiple biological evaluations were performed to determine their cytotoxicity, cyto-protective effects, antioxidant effect as well as druglike properties. These compounds provide new cores for the further design and optimization, with the aim to discover new ChEs inhibitors for the treatment of AD.  相似文献   

19.
For various neurodegenerative disorders like Alzheimer's and Parkinson’s diseases, selective and reversible MAO‐B inhibitors have a great therapeutic value. In our previous study, we have shown that a series of methoxylated chalcones with F functional group exhibited high binding affinity toward human monoamine oxidase‐B (hMAO‐B). In continuation of our earlier study and to extend the understanding of the structure–activity relationships, a series of five new chalcones were studied for their inhibition of hMAO. The results demonstrated that these compounds are reversible and selective hMAO‐B inhibitors with a competitive mode of inhibition. The most active compound, (2E)‐1‐(4‐hydroxyphenyl)‐3‐[4‐(trifluoromethyl)phenyl]prop‐2‐en‐1‐one, exhibited a Ki value of 0.33 ± 0.01 μm toward hMAO‐B with a selectivity index of 26.36. A molecular docking study revealed that the presence of a H‐bond network in hydroxylated chalcone with the N(5) atom of FAD is crucial for MAO‐B selectivity and potency.  相似文献   

20.
Abstract— Nicotine binds to homogenates of lobster walking leg nerve (Kd= 1.1 ± 0.3 μm , Bmax= 2.4 ± 0.5 nmol/g wet tissue), horseshoe crab leg nerve (Kd= 0.11 ± 0.06 μm , Bmax= 1.3 ± 0.6nmol/g), and kidney from 18-month-old rats (Kd= 0.8 ± 0.2 μm , Bmax= 23 ± 9 nmol/g). The pharmacological sensitivities of nicotine binding to lobster and horseshoe crab leg nerve homogenates are similar to that of the axonal cholinergic binding macromolecule (ACBM) (Denburg et al., 1972) of lobster leg. nerve membrane, while the binding to rat kidney is sensitive to α-bungarotoxin but not atropine or curare. There was no nicotine binding to rat heart or spleen, or to kidney from younger rats; little or no binding to blue crab nerve or to Torpedo electroplax motor nerve; and little binding (around 0.1 nmol/g) to rat liver. [3H]α-Bungarotoxin bound reversibly (0.17 nmol/g) to lobster leg nerve membrane The implications of these results for the distribution and function of the ACBM, and for the specificity of α-bungarotoxin, are discussed.  相似文献   

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