Binding sites for [3H]-acetylcholine and 125I-alpha-bungarotoxin in the optic ganglion of Loligo pealii

1. In the optic ganglion of Loligo pealii, binding sites for [3H]-acetylcholine (KD: 5.2 x 10(-7) M; Bmax: 1.7 x 10(-11) mol/g tissue) and 125I-alpha-bungarotoxin (KD: 3.3 x 10(-9) M; Bmax: 9.7 x 10(-11) mol/g tissue) were observed. 2. Both sites are blocked by nicotinic compounds, but differ significantly in their affinity for individual ligands, with the acetylcholine site preferentially binding agonists, and the toxin site, antagonists. 3.The acetylcholine site is substantially more thermolabile than the toxin site. 4. A partial separation of the two binding activities is accomplished by sucrose density centrifugation. 5. These observations and a comparison with other tissues (Torpedo californica electroplaque; chick optic lobe; rat brain) suggest the presence, in the squid, of more than one kind of neuronal nicotinic receptor.     

Insulin-like growth factor II binding to the type I somatomedin receptor. Evidence for two high affinity binding sites

We have previously shown that the antireceptor antibody alpha IR-3 inhibits binding of 125I-somatomedin-C/insulin-like growth factor I (Sm-C/IGF-I) to the 130-kDa alpha subunit of the type I receptor in human placental membranes, but does not block 125I-insulin-like growth factor II (IGF-II) binding to a similar 130-kDa complex in these membranes. To determine whether the 130-kDa 125I-IGF-II binding complex represents a homologous receptor or whether 125I-IGF-II binds to the type I receptor at a site that is not blocked by alpha IR-3, type I receptors were purified by affinity chromatography on Sepharose linked alpha IR-3. The purified receptors bound both 125I-Sm-C/IGF-I and 125I-IGF-II avidly (KD = 2.0 X 10(-10) M and 3.0 X 10(-10) M, respectively). The maximal inhibition of 125I-Sm-C/IGF-I binding by the antibody, however, was 62% while only 15% of 125I-IGF-II binding was inhibited by alpha IR-3. In the presence of 500 nM alpha IR-3, Sm-C/IGF-I bound with lower affinity (KD = 6.5 X 10(-10) M) than IGF-II (KD = 4.5 X 10(-10) M) and IGF-II was the more potent inhibitor of 125I-Sm-C/IGF-I binding. These findings suggest that the type I receptor contains two different binding sites. The site designated IA has highest affinity for Sm-C/IGF-I and is blocked by alpha IR-3. Site IB has higher affinity for IGF-II than for Sm-C/IGF-I and is not blocked by alpha IR-3.     

Endocrine aging in C57 BL mice--II. Dynamics of estrogen receptors in the hypothalamic-pituitary axis

Specific cytosolic and nuclear binding sites for estrogens were measured in the hypothalamic-pituitary axis (HPA) of young (4-8 months) and old (16-18 months) C57 BL mice in order to determine any age-related alteration in hormone-receptor interaction. Our results indicated no age differences in the affinity (KD = 0.89 +/- 0.03 (SEM) vs 1.09 +/- 0.2 X 10(-9) M), the specificity, the sedimentation profile (6 s) or in the number (98.9 +/- 4.9 vs 84.4 +/- 2.3 fmol/mg protein) of unoccupied estrogen binding sites in the cytosols. Estradiol administration to young mice induced a complete translocation of cytosolic estrogen receptors to the nucleus, and two types of nuclear binding sites were observed: Type I were specific for estrogens with high affinity (KD = 0.51 +/- 0.06 X 10(-9) M) and low binding capacity (115.1 +/- 22.7 fmol/mg DNA) and sedimented in the 4.0 s area, while Type II binding sites showed a much higher capacity and lower affinity for R2858. HPA nuclear suspensions of aged untreated mice showed undetectable (less than 50 fmol/mg DNA) levels of nuclear estrogen receptors and E2 pre-treatment resulted in a significant increase in both types of binding sites. While no significant changes in the physicochemical characteristics of these nuclear receptors were observed, when compared to young animals, aging was manifested by a translocation defect in the HPA of C57 BL mice. These results suggest aging changes in the endocrine regulating centers of the brain with defective activation of estrogen receptors.     

Prostaglandin-sensitive adenylate cyclase of a murine macrophage-like cell line (P388D1): II. Isolation and partial characterization of PGE2-binding proteins

Properties of prostaglandin (PG) E2 binding sites of a murine macrophage cell line (P388D1) were investigated. The specific binding of [3H]-PGE2 to intact P388D1 cells at 4 degrees C in the presence of cytochalasin D (10 micrograms/ml) approached saturation at concentration greater than 7.5 X 10(-9) M, and could be displaced most effectively by unlabeled PGE2 and less effectively by unlabeled PGI2. The Scatchard analysis of the binding data clearly indicated the heterogeneity with respect to the PGE2 binding affinity and showed the presence of about 3.9 fmol/10(8) cells of the high affinity sites (KD = 1.1 X 10(-9) M) and about 24 fmol/10(8) cells of the low affinity sites (KD = 2 X 10(-8) M). PGE2-binding proteins were isolated from the detergent lysate of the radiolabeled P388D1 cells by affinity chromatography on Sepharose 4B coupled to PGE2. The affinity-isolated materials were further purified by successive use of Sephadex G-100 gel filtration and isoelectric focusing in the presence of dithiothreitol (1 mM) and Triton X-100 (0.5%). The final step yielded about 0.25% of the original radioactivity, which sharply focused as a single peak at pH near 6.5. The electrofocused PGE2-binding proteins migrated as a single band with a m.w. of 95,000 during SDS-PAGE. The electrofocused PGE2-binding proteins bound specifically to [3H]-PGE2 but showed again the heterogeneity with respect to their affinity.     

Serotonin storage pools in basophil leukemia and mast cells: characterization of two types of serotonin binding protein and radioautographic analysis of the intracellular distribution of [3H]serotonin

We studied binding of serotonin to protein(s) derived from rat basophil leukemia (RBL) cells and mast cells. We found two types of serotonin binding protein in RBL cells. These proteins differed from one another in molecular weight and eluted in separate peaks from sephadex G-200 columns. Peak I protein (KD = 1.9 X 10(-6) M) was a glycoprotein that bound to concanavalin A (Con A); Peak II protein (KD1 = 4.5 X 10(-8) M; KD2 = 3.9 X 10(-6) M) did not bind to Con A. Moreover, binding of [3H]serotonin to protein of peak I was sensitive to inhibition by reserpine, while binding of [3H]serotonin to protein of peak II resisted inhibition by that drug. Other differences between the two types of binding protein were found, the most significant of which was the far more vigorous conditions of homogenization required to extract peak I than peak II protein. Neither peak I nor peak II protein resembled the serotonin binding protein (SBP) that is found in serotonergic neurons of the brain and gut. Electron microscope radioautographic analysis of the intracellular distribution of [3H]serotonin taken up in vitro by RBL cells or in vivo by murine mast cells indicated that essentially all of the labeled amine was located in cytoplasmic granules. No evidence for a pool in the cytosol was found and all granules were capable of becoming labeled. The presence of two types of intracellular serotonin binding proteins in these cells may indicate that there are two intracellular storage compartments for the amine. Both may be intragranular, but peak I protein may be associated with the granular membrane while peak II protein may be more free within the granular core. Different storage proteins may help to explain the differential release of amines from mast cell granules.     

Characterization of a cyclic AMP-resistant Chinese hamster ovary cell mutant containing both wild-type and mutant species of type I regulatory subunit of cyclic AMP-dependent protein kinase

We have characterized a cyclic AMP-resistant Chinese hamster ovary (CHO) cell mutant in which one of two major species of type I regulatory subunit (RI) of cyclic AMP-dependent protein kinase is altered. Wild-type CHO cell extracts contain two cyclic AMP-dependent protein kinase activities. As shown by DEAE-cellulose chromatography, there is a peak of type I protein kinase activity in mutant extracts, but the type II protein kinase activity is considerably reduced even though free type II regulatory subunit (RII) is present. The type I kinase from the mutant has an altered RI (RI*) whose KD for the binding of 8-N3[32P] cAMP (KD = 1.3 X 10(-5) M) is increased by more than 200-fold compared to RI from the wild-type enzyme (KD = 5.5 X 10(-8) M). No differences were found between the catalytic subunits from the wild-type and mutant type I kinases. A large portion of RI in mutant and wild-type extracts is present in the free form. The RI* derived from mutant type I protein kinase shows altered labeling by 8-N3[32P]cAMP (KD = 1.3 X 10(-5) M) whereas the free RI from the mutant is labeled normally by the photoaffinity label (KD = 7.2 X 10(-8) M), suggesting that the RI* which binds to the catalytic subunit is functionally different from the free form of RI. The decreased amount of type II kinase activity in the mutant appears to be due to competition of RI* with RII for binding to the catalytic subunit. Translation of mRNA from wild-type CHO cells results in the synthesis of two different charge forms of RI, providing biochemical confirmation of two different species of RI in CHO cells. Additional biochemical evidence based on isoelectric focusing behavior of 8-N3[32P]cAMP-labeled RI species and [35S]methionine-labeled RI from mutant and wild-type extracts confirms the charge heterogeneity of RI species in CHO cells. These genetic and biochemical data taken together are consistent with the conclusion that there are at least two different species of RI present in CHO cells and that one of these species is altered in the mutant analyzed in this work.     

B2-kinin receptor like binding in rat glomerular membranes

Incubation of a radiolabeled bradykinin analog, [125I]-Tyr8-BK with a crude membrane preparation obtained from isolated rat glomeruli revealed a time dependent binding. The binding was saturable, reversible and was a linear function of protein membrane concentration. The radiolabeled Tyr8-BK bound to a single class of binding sites with an equilibrium dissociation constant (KD) of 3.9 +/_ 0.7 nM and a density (Bmax) of 31 +/- 5 fmol/mg protein. The BK-receptor complex was not affected by angiotensin II or by arginine vasopressin and atrial natriuretic factor. BK binding was reversed by bradykinin (Ki = 0.3 10(-9) M), and by other kinin analogs in the following order of potency: Lys-BK, Met-Lys-BK, Thi5,8-D Phe7-BK. However, Des-Arg9-BK had no effect on binding of the radiolabelled BK. These results are consistent with the presence of a B2-kinin like receptor in rat glomeruli.     

Nerve Growth Factor Receptors in Human Neuroblastoma Cells

Receptors for the nerve growth factor protein (NGFR) present in the human neuroblastoma cell line LAN-1 were characterized. LAN-1 cells display high-affinity (type I, with KD value of 5.9 X 10(-11) M) and low-affinity (type II, with KD value of 9.2 X 10(-9) M) binding to NGF. NGFR were fractionated by preparative isoelectric focusing in a granulated gel (PEGG). High-affinity binding was found in the 5.9-6.2 pH region of the PEGG, and low-affinity binding in the 4.6-4.8 and 8.8-9.3 pH ranges. After further analysis by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) we observed both 92.5- and 200-kDa molecular species associated with NGF binding activity. The 200-kDa protein was found in fractions displaying high-affinity NGF binding and the 92.5-kDa protein in fractions displaying low-affinity NGF binding. Equilibrium binding analysis of NGF in PEGG fractions confirmed the presence of two specific saturable binding sites with KD values similar to those observed for whole dissociated cells. When NGFR II activity from the acidic region of the PEGG chromatogram was incubated with NGFR II from the basic region of the PEGG chromatogram, there was no change in NGF binding or in the number of apparent NGF receptors. However, incubation of these same fractions with a fraction having only NGFR I showed an apparent increase in high-affinity NGF binding and a decrease in low-affinity NGF binding. Immunoprecipitation of this "mixed" fraction and analysis on SDS-PAGE under reduced and nonreduced conditions showed 200-kDa and 92.5-kDa proteins under nonreduced conditions and a 92.5-kDa protein under reduced conditions. Our findings are consistent with the hypothesis that there are two distinct NGF receptors in NGF-responsive cells. The interconvertibility of low- and high-affinity receptors and the possible existence of a modulator type protein or of "silent" type receptors are also in agreement with our findings.     

Correlation of changes in cardiac calcium channels with hemodynamics in Syrian hamster cardiomyopathy and heart failure

We compared hemodynamics with [3H]nitrendipine (calcium channel) binding to cardiac membranes from Bio 14.6 cardiomyopathic Syrian hamsters at 4 and 10 months with their F1B controls. A 50% increase in the number (Bmax) of nitrendipine binding sites (calcium channels) was seen only in the 4 month old myopathic vs controls (Bmax = 468 +/- 11 vs 309 +/- 10 fmol/mg prot with no change in affinity (KD) (KD = .65 +/- .12 vs .75 +/- .14 nM), while no differences in Bmax or KD were seen at 10 months (Bmax = 375 +/- 9 vs 362 +/- 7 fmol/mg prot/KD = .82 +/- .18 vs .89 +/- .17 nM) myopathic vs control respectively. Hemodynamic studies revealed no significant differences in cardiac output, cardiac index, stroke volume, heart rate, mean arterial pressure, peripheral resistance, body weight, heart weight at 4 months, but a significant decrease in peripheral resistance (1120 +/- 360 vs 2080 +/- 240) increase in body weight (118 +/- 2 vs 94 +/- 2 grams) and heart weight (97 +/- 5 vs 78 +/- 2 gms/100 gms body weight) in 10 month myopathic vs control animals. We conclude that the onset of cardiomyopathy at 4 months is associated with a selective increase in calcium channel binding sites and heart failure at 10 months is associated with a relative decrease in these sites.     

Atypical beta-adrenergic receptor in 3T3-F442A adipocytes. Pharmacological and molecular relationship with the human beta 3-adrenergic receptor.

Expression of ligand binding properties for an atypical beta-adrenergic receptor (beta-AR) subtype was studied during the adipose differentiation of murine 3T3-F442A cells and compared with that of the human beta 3-AR expressed in Chinese hamster ovary cells stably transfected with the human beta 3-AR gene (CHO-beta 3 cells) Emorine, L. J., Marullo, S., Briend-Sutren, M. M., Patey, G., Tate, K., Delavier-Klutchko, C., and Strosberg, A. D. (1989) Science 245, 1118-1121). 3T3-F442A adipocytes exhibited high and low affinity binding sites for (-)-4-(3-t-butylamino-2-hydroxypropoxy) [5,7-3H]benzimidazole-2-one ((-)-[3H]CGP-12177) (KD = 1.2 and 38.3 nM) and (-)-[125I]iodocyanopindolol ([125I]CYP) (KD = 47 and 1,510 pM). The high affinity sites corresponded to the classical beta 1- and beta 2-AR subtypes whereas the KD values of the low affinity sites for the radioligands were similar to those measured in CHO-beta 3 cells (KD = 28 nM and 1,890 pM for (-)-[3H]CGP12177 and [125I]CYP, respectively). These low affinity sites were undetectable in preadipocytes but represented about 90% of total beta-ARs in adipocytes. The atypical beta-AR and the human beta 3-AR add similarly low affinities (Ki = 3-5 microM) for (+/-)-(2-(3-carbamoyl-4-hydroxyphenoxy)ethylamino-3)-(4-(1-methyl- 4- trifluormethyl-2-imidazolyl)-phenoxy)-2-propanol methane sulfonate (CGP20712A) or erythro-(+/-)-1-(7-methylindan-4-yloxy)-3-isopropylaminob utan-2-ol (ICI118551), highly selective beta 1- and beta 2-AR antagonists, respectively, in agreement with the poor inhibitory effect of the compounds on (-)-isoproterenol (IPR)-stimulated adenylate cyclase activity. Atypical beta-AR and beta 3-AR had an affinity about 10-50 times higher for sodium-4-(2-[2-hydroxy-2-(3-chlorophenyl)ethylamino]propyl)phenoxyace tate sesquihydrate (BRL37344) than the beta 1-AR subtype. This correlates with the potent lipolytic effect of BRL37344 in adipocytes. The rank order of potency of agonists in functional and binding studies was BRL37344 greater than IPR less than (-)-norepinephrine greater than (-)-epinephrine both in 3T3 adipocytes and CHO-beta 3 cells. As in CHO-beta 3 cells, the classical beta 1- and beta 2-antagonists CGP12177, oxprenolol, and pindolol were partial agonists in adipocytes. Although undetectable in preadipocytes, a major mRNA species of 2.3 kilobases (kb) and a minor one of 2.8 kb were observed in adipocytes by hybridization to a human beta 3-AR specific probe.(ABSTRACT TRUNCATED AT 400 WORDS)     

钙调神经磷酸酶B亚基及钙调素的EPR研究

根据顺磁离子Mn~(2+)的取代特性,用EPR方法研究了钙调神经磷酸酶B亚基与其4个Ca~(2+)的结合位点,以及它们亲和力的细微差别。并同时进行了钙调素的对比研究。实验和Scatchard作图表明,B亚基有4个Ca~(2+)结合位点,2个高亲和力结合位点,其解离常数为4×10~(-6)mol/L;2个低亲和力结合位点,解离常数为9×10~(-5)mol/L。钙调素也有2个Ca~(2+)高亲和力结合位点,其解离常数为8×10~(-6)mol/L,2个低亲和力结合位点,解离常数为7×10~(-5)mol/L。钙调神经磷酸酶B亚基和钙调素Mn~(2+)结合位点的EPR研究对B亚基和钙调素在共同调节钙调神经磷酸酶中的作用提供了有用的信息。     

Binding of (3H)prostaglandin E1 to putative receptors linked to adenylate cyclase of cultured cell clones.

A method for assessing the binding of 3H-labeled prostaglandin E1 ([3H]PGE1) to cell membranes has been developed and used to study the interaction of [3H]PGE1 with membranes from cultured mammalian cells. Receptor sites were identified by correlation of the potency of a series of compounds to compete for [3H]PGE1 binding sites and to stimulate adenylate cyclase activity, by correlation of rates of binding and change in enzyme activity, and by the correspondence of [3H]PGE1-binding activity with the presence or absence of PGE1-sensitive adenylate cyclase in several clones. In clone B82, a murine L-cell, [3H]PGE1 binds with an activation energy of 14 kcal/mol to a class of sites with an affinity of 0.5 X 10(8) M-1 and a capacity of 150 fmol/mg of protein. Concentration dependence of adenylate cyclase activation by PGE1 (KD =30 nM) and kinetic analysis of [3H]PGE1 binding (k1 = 4 X 10(6) liters/mol/min, k-1 0.15/min) verify this affinity. Concentration dependence and specificity of binding and activation of adenylate cyclases in neuroblastoma clone N4TG1 and N18TG2 substantiate the method. In several clones that lack PGE1-responsive adenylate cyclase, no specific [3H]PGE1 binding is detectable.     

Binding of human blood-coagulation Factors IXa and X to phospholipid membranes.

A simple centrifugation technique has been developed to study the interaction of human coagulation Factors IXa and X with phospholipid membranes. In the presence of Ca2+, equimolar phosphatidylserine/phosphatidylcholine membranes form tight complexes with Factor X (KD = 2.8 X 10(-8) M); the KD is independent of the phospholipid concentration. Binding sites are available for about 2 mmol of Factor X/mol of phospholipid. Factor IXa has a slightly higher affinity for the phospholipid membrane (KD = 1.2 X 10(-8)M), and competes with Factor X for binding. The experimentally observed competition between Factor X and Factor IXa is in agreement with a model that describes the binding of two distinct ligands to a single class of independent binding sites.     

Silver(I) complexes with DNA and RNA studied by Fourier transform infrared spectroscopy and capillary electrophoresis

Ag(I) is a strong nucleic acids binder and forms several complexes with DNA such as types I, II, and III. However, the details of the binding mode of silver(I) in the Ag-polynucleotides remains unknown. Therefore, it was of interest to examine the binding of Ag(I) with calf-thymus DNA and bakers yeast RNA in aqueous solutions at pH 7.1-6.6 with constant concentration of DNA or RNA and various concentrations of Ag(I). Fourier transform infrared spectroscopy and capillary electrophoresis were used to analyze the Ag(I) binding mode, the binding constant, and the polynucleotides' structural changes in the Ag-DNA and Ag-RNA complexes. The spectroscopic results showed that in the type I complex formed with DNA, Ag(I) binds to guanine N7 at low cation concentration (r = 1/80) and adenine N7 site at higher concentrations (r = 1/20 to 1/10), but not to the backbone phosphate group. At r = 1/2, type II complexes formed with DNA in which Ag(I) binds to the G-C and A-T base pairs. On the other hand, Ag(I) binds to the guanine N7 atom but not to the adenine and the backbone phosphate group in the Ag-RNA complexes. Although a minor alteration of the sugar-phosphate geometry was observed, DNA remained in the B-family structure, whereas RNA retained its A conformation. Scatchard analysis following capillary electrophoresis showed two binding sites for the Ag-DNA complexes with K(1) = 8.3 x 10(4) M(-1) for the guanine and K(2) = 1.5 x 10(4) M(-1) for the adenine bases. On the other hand, Ag-RNA adducts showed one binding site with K = 1.5 x 10(5) M(-1) for the guanine bases.     

Cyclic 3',5'-adenosine monophosphate-dependent kinase and phosphoproteins in human amnion

3',5'-Cyclic adenosine monophosphate (cAMP) modulates prostaglandin production in human amnion membranes. The major effects of cAMP are presumably mediated through the phosphorylation of specific regulatory phosphoproteins following cAMP activation of cAMP-dependent protein kinase. Cyclic AMP-dependent protein kinase and phosphoproteins have not previously been characterized in human amnion. Total homogenates, cytosol, and membrane fractions from human amnion were examined for [3H]cAMP binding activity and cAMP-dependent kinase activity. cAMP-dependent kinase activity was barely detectable in crude amnion fractions. Cytosol was therefore partially purified by DEAE column chromatography for further examination. Two peaks of coincident [3H]cAMP binding and cAMP-dependent kinase activity were demonstrated at 70 and 140 mM NaCl, characteristic of the Type I and Type II cAMP-dependent protein kinase isozymes. [3H]cAMP binding to the material from both peak fractions was saturable and reversible. Scatchard analysis of [3H]cAMP binding to the peak fractions was linear for peak I and curvilinear for peak II. Assuming a one-site model, [3H]cAMP binding to the Type I isozyme showed a KD = 4.17 x 10(-8) M and Bmax = 73 pmole/mg protein; using a two-site model, [3H]cAMP binding to the high-affinity site for the Type II isozyme had a KD = 3.94 x 10(-8) M and Bmax = 6.3 pmole/mg protein. Other cyclic nucleotides competed for these [3H]cAMP binding sites with a potency order of cAMP much greater than cGMP greater than (BU)2cAMP.cAMP caused a dose-dependent increase in cAMP-dependent kinase activity in the peak fractions; half-maximal activation was observed with 5.0 x 10(-8) M cAMP. The ability of cAMP to increase phosphorylation of endogenous proteins in both crude amnion cytosol and cytosol from cultures of amnion epithelial cells was assessed using [32P]ATP, SDS-polyacrylamide gel electrophoresis and autoradiography. cAMP stimulated 32P incorporation into three proteins having Mr = 80,000, 54,000, and 43,000 (P less than .01). Half-maximal 32P incorporation into these proteins occurred at 1.0 x 10(-7) M cAMP. cAMP-dependent kinase is present in human amnion; specific cAMP-enhanced phosphoproteins are also present. Hormones elevating cAMP levels in amnion may exert their effects by activating cAMP-dependent kinase and phosphorylating these phosphoproteins.     

Characterization of Binding Sites for the Angiotensin II Antagonist 125I-[Sarc1,Ile8]-Angiotensin II on Murine Neuroblastoma N1E-115 Cells

The murine neuroblastoma N1E-115 cell line contains binding sites for the angiotensin II (Ang II) receptor antagonist 125I-[Sarc1,Ile8]-Ang II (125I-SARILE). Binding of 125I-SARILE to N1E-115 membranes was rapid, reversible, and specific for Ang II-related peptides. The rank order potency of 125I-SARILE binding was the following: [Sarc1]-Ang II = [Sarc1,Ile8]-Ang II greater than Ang II greater than Ang III = [Sarc1,Thr8]-Ang II much greater than Ang I. Scatchard analysis of membranes prepared from confluent monolayers revealed a homogenous population of high affinity (KD = 383 +/- 60 pM) binding sites with a Bmax of 25.4 +/- 1.6 fmol/mg of protein. Moreover, the density, but not the affinity, of the binding sites increased as the cells progressed from logarithmic to stationary growth in culture. Finally, agonist, but not antagonist, binding to N1E-115 cells was regulated by guanine nucleotides. Collectively, these results suggest that the murine neuroblastoma N1E-115 cell line may provide a useful model in which to investigate the signal transduction mechanisms utilized by neuronal Ang II receptors.     

High affinity epidermal growth factor receptors on the surface of A431 cells have restricted lateral diffusion

Rhodamine-labelled epidermal growth factor (Rh-EGF) was shown to bind to A431 cells grown at low density both to a small number of high affinity receptors (KD = 2.8 X 10(-10) M; fraction of total binding sites approximately 0.12) and also to a large number of low affinity receptors (KD = 4 X 10(-9) M; fraction of total binding sites approximately 0.88). Measurements of the lateral diffusion of EGF receptors on the cell surface were made using Rh-EGF and the technique of fluorescence photobleaching recovery. The high affinity receptors (labelled with 1.6 X 10(-10) M Rh-EGF, 5% of EGF binding sites occupied) did not show lateral mobility over the temperature range 3 degrees-37 degrees C. The low affinity receptors (labelled with 2.4 X 10(-7) M Rh-EGF, 90% of EGF sites occupied) showed at least 75% fluorescence recovery after photobleaching, and lateral diffusion coefficients of approximately 2 X 10(-10) cm2/s. These results show that the two populations of EGF receptors defined by binding studies differ in their freedom to diffuse laterally. The observation that the high affinity receptors are immobile indicates that lateral diffusion of receptors, at least over a distance of a few hundred nanometres or more, may not be required for the action of low concentrations of EGF.     

Studies on the mechanism of electron transport in the bc1-segment of the respiratory chain in yeast. II. The binding of antimycin to mitochondrial particles and the function of two different binding sites.

1. In mitochondrial particles antimycin binds to two separate specific sites with dissociation constants KD1 less than 4 - 10(-13) M and KD2 = 3 - 10(-9) M, respectively. 2. The concentrations of the two antimycin binding sites are about equal. The absolute concentration for each binding site is about 100 - 150 pmol per mg of mitochondrial protein. 3. Antimycin bound to the stronger site mainly inhibits NADH-and succinate oxidase. Binding of antimycin to the weaker binding site inhibits the electron flux to exogenously added cytochrome c after blocking cytochrome oxidase by KCN. 4. Under certain conditions cytochrome b and c1 are dispensible components for antimycin-sensitive electron transport. 5. A model of the respiratory chain in yeast is proposed which accounts for the results reported here and previously. (Lang, B., Burger, G., and Bandlow, W. (1974) Biochim. Biophys. Acta 368, 71-85).     

Interleukin 1 induces NF-kappa B through its type I but not its type II receptor in lymphocytes.

It is not known whether one or both of the interleukin 1 (IL1) receptors mediates the induction of the DNA-binding protein NF-kappa B. Nuclear extracts of the murine lines EL4.NOB.1 and 70Z/3, which bear the type I (80 kDa) and type II (67 kDa) IL1 receptor, respectively, were analyzed by an electrophoretic mobility shift assay. A 265-base pair sequence of the human serum amyloid A gene or a synthetic oligonucleotide each containing the NF-kappa B site were used as the DNA probes. IL1 induction of NF-kappa B was rapid (optimal at 15-30 min) and transient in both cell types. The IL1 receptor antagonist (IL1ra), which binds strongly to the type I receptor, inhibited the NF-kappa B response in both cell lines. IL1ra did not bind to the type II receptor on 70Z/3 cells as judged by competition for binding with 125I-IL1 alpha. When 125I-IL1ra binding to 70Z/3 cells was measured, a small number (10/cell) of high affinity sites (Kd = 5 x 10(-12) M) were detected. These were likely to have been type I receptor because an antibody to this inhibited the NF-kappa B induction in 70Z/3 cells (as well as EL4). Potential signal transduction mechanisms involving protein kinase C or oxygen radicals were studied. Phorbol 12-myristate 13-acetate induced NF-kappa B with a similar time course to IL1 in 70Z/3 but only after 4 h in EL4.IL1 was unaffected by a protein kinase C inhibitor (staurosporine). H2O2 did not mimic IL1, and IL1 was not inhibited by an antioxidant. The type I receptor mediates the induction of NF-kappa B in response to IL1 via a signaling mechanism that still remains to be identified.     

entaaification of Atrial Natriuretic Factor Receptor of Neuroblastoma N4TG1 Cells: Binding Characteristics and Photoaffinity Labeling

We have found specific receptors for atrial natriuretic factor (ANF) in cultured neuroblastoma cells (N4TG1) of peripheral ganglionic origin. Scatchard analysis of the displacement binding revealed noninteracting, single-class binding sites with a KD of 1 X 10(-10) M and a density (Bmax) of 110,000-150,000 sites/cell. The cell-bound 125I-ANF was displaced by unlabeled ANF in a dose-dependent manner. Hormones unrelated to ANF such as angiotensins, adrenocorticotropic hormone, or arginine vasopressin were ineffective in displacing the cell-bound radioactivity. Using azidobenzoyl-125I-ANF as a photoaffinity ligand, an ANF receptor with an apparent Mr of 138,000 was identified by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and autoradiography. The addition of unlabeled ANF (1 microM) to the incubation medium completely abolished the labeling of this protein band, but atriopeptin I (1 microM) or angiotensins I, II, and III (each 1 microM) were not effective in inhibiting the affinity labeling. The treatment of the neuroblastoma cells with ANF stimulated intracellular cyclic GMP levels in a dose-dependent manner with an EC50 of 5 nM. ANF (1 X 10(-7) M) stimulated cyclic GMP accumulation in less than 5 min by 30-fold as compared to the controls.