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R J Lefkowitz

Publications and source records attributed to R J Lefkowitz.

At least 541 records · Page 30Linked to original sources
PubMed1977

Resolution of beta-adrenergic receptor binding and adenylate cyclase activity by gel exclusion chromatography.

The frog erythrocyte membrane provides an excellent model system for the study of beta-adrenergic receptor-adenylate cyclase interactions since it possesses an adenylate cyclase enzyme which is very responsive to catecholamines. The purpose of these studies was to evaluate directly whether the functions of receptor binding and adenylate cyclase activity are carried out by a single macromolecule or separable molecular entities. Obtaining this information is a first step in understanding at a molecular level how receptor binding is "coupled" to enzyme activation. Binding and cyclase activities were solubilized from the frog erythrocyte membrane with digitonin and were observed to partition independently during gel exclusion chromatography in the presence of solubilizing detergent. This finding documents that the beta-adrenergic receptor and adenylate cyclase enzyme are, in fact, separable macromolecules. Under the particular experimental conditions employed, the elution of beta-adrenergic receptor binding on Sepharose 6B was not altered by the absence or presence of beta-adrenergic agonist or antagonist ligands or by exposure of the membranes prior to solubulization to the guanyl nucleotide analog, guanyl-5'-yl imidodiphosphate.

Adenylyl Cyclases↗
PubMed1977

Structure and biological activity of (-)-[3H]dihydroalprenolol, a radioligand for studies of beta-adrenergic receptors.

(-)-Alprenolol is a potent competitive beta-adrenergic antagonist. "(-)-[3H]Alprenolol", a radioactive form of this agent produced by catalytic reduction with tritium, has recently been used successfully as a radioligand for direct studies of beta-adrenergic receptors. In this communication it is documented that the compound formed by catalytic reduction of (-)-alprenolol with tritium gas is the saturated product (-)-[3H]dihydroalprenolol in which tritium is added across the double bond and exchanged into the adjacent benzylic position. No exchange into the aromatic ring was observed. These conclusions were substantiated by results obtained on hydrogenation and deuteration of (-)-alprenolol. The biological activity of (-)-[3H]dihydroalprenolol, dihydroalprenolol, and alprenolol was also shown to be identical as assessed by direct ligand binding and inhibition of catecholamine-stimulated adenylate cyclase.

Adenylyl Cyclase Inhibitors↗
PubMed1977

Catecholamine binding to the beta-adrenergic receptor.

The adenylate cyclase-coupled beta-adrenergic receptors of frog erythrocyte membranes have been identified by direct radioligand binding techniques using the potent catecholamine agonist (+/-)[3H]hydroxybenzylisproterenol (2-[3, 4-dihydroxyphenyl]-2-hydroxy-1', 1'-dimethyl-2'-[4-hydroxyphenyl]-diethylamine). The successful experimental conditions included the use of (i) high concentrations of catechol and ascorbic acid to suppress nonreceptor binding, (ii) a very potent radiolabeled catecholamine (10 times more potent than isoproterenol), and (iii) membranes rich in binding sites for beta-adrenergic receptors. Thus, previous problems in accomplishing successful catecholamine binding to the beta-receptors have been overcome. The binding sites identified with (+/-)[3H]hydroxybenzylisoproterenol in the erythrocyte membranes have all the characteristics expected of true beta-adrenergic receptors. These include rapidity of binding, saturability, specificity for beta-agonists and antagonists, and stereospecificity [(-)isomers more potent than (+)isomers]. Physiologically inactive compounds containing a catechol moiety do not compete for occupancy of these binding sites. Dissociation of the radiolabeled agonist from the receptors is slow and incomplete in the absence of guanine nucleotides. In the presence of nucleotide, however, dissociation is rapid and complete. beta-Adrenergic agonists and antagonists compete for the (+/-)[3H]hydroxybenzylisoproterenol binding sites in a fashion parallel to their competition for the receptors, as previously delineated with the beta-adrenergic antagonist (-)[3H]dihydroalprenolol.

Adrenergic beta-Antagonists↗
PubMed1977

Specific receptor sites for chemotactic peptides on human polymorphonuclear leukocytes.

Synthetic N-formylmethionyl peptides are chemotactic attractants for human polymorphonuclear leukocytes. The well-defined structure-activity relationship of these peptides in eliciting a chemotactic response suggests that the interaction of the peptides with a specific cellular binding site may initiate chemotaxis. By using tritiated N-formylmethionyl-leucyl-phenylalanine (fMet-Leu-[3H]Phe), a potent chemotactic peptide with high specific radioactivity, we have directly identified binding sites on human polymorphonuclear leukocytes. Binding of fMet-Leu-[3H]Phe to polymorphonuclear leukocytes is rapid (t1/2 less than 2 min) and reversible. The equilibrium dissociation constant (KD) for the interaction of fMet-Leu-[3H-A1Phe with the binding site is 12-14 nM at 37 degrees. The number of binding sites is approximately 2000 per cell. The specificity of the binding sites for a series of N-formylmethionyl peptides exactly reflects the specificity of the chemotactic response to the peptides in that they compete for the binding sites and initiate chemotaxis with the same order of potency (fMet-Leu-Phe greater than fMet-Met-Met greater than fMet-Phe greater than fMet-Leu greater than fMet),fPhe-Met is a competitive antagonist of the chemotactic activity of N-formylmethionyl peptides and has a calculated KD of 6x10-5 M. FPhe-Met also half-maximally inhibits binding of fMet-Leu[3H]Phe binding was the highest in polymorphonuclear leukocytes. No binding of fMet-Leu-[3H]Phe to human erythrocytes could be detected. These data indicate that fMet-Leu-[3H]Phe can be used to identify binding sites for chemotactic peptides on human polymorphonuclear leukocytes. It is likely that these binding sites initiate the specific response of motile cells to N-formylmethionyl peptides.

Binding Sites↗
PubMed1977

Ectopic beta-adrenergic receptor binding sites. possible molecular basis of aberrant catecholamine responsiveness of an adrenocortical tumor adenylate cyclase.

The molecular basis for the aberrant catecholamine responsiveness of the adenylate cyclase of adrenocortical carcinoma 494 was explored. The adenylate cyclase of this corticosteroid-producing, transplanted, adrenal cancer of the rat was stimulated not only by adrenocorticotropic hormone and fluoride, but also by the beta-adrenergic agonist, isoproterenol. The adenylate cyclase of normal adrenal tissue was unresponsive to isoproterenol. Direct binding studies with the specific high affinity B-adrenergic ligand, (-)[3H]dihydroalprenolol, demonstrated the pressure of 0.094 pmol of specific binding sites per milligram of tumor membrane protein. By contrast, normal adrenal membranes contained too few binding sites to accurately measure and study using these techniques. The tumor binding sites had high affinity for (-)[3H] dihydroalprenolol with an equilibrium dissociation constant of 2.1 nM. Adrenergic agonists competed for the binding sites in an order of potency, [(-) isoproterenol greater than (-) epinephrine (-) norepinephrine], paralleling their order of potency as beta-adrenergic agonists. The beta-adrenergic antagonist, (-) propranolol, competed for binding, causing half-mzximal inhibition of specific binding at a concentration of 6 nM. The alpha-adrenergic antagonist, phentolamine, and several catecholamine metabolites and precursors did not effectively compete for the binding sites at high concentrations. Binding was stereospecific, the (+) stereoisomers of beta-adrenergic agonists and antagonists requiring 40- to 300-fold higher concentrations than the corresponding (-) stereoisomers to half maximally inhibit (-) [3H] dihydroalprenolol binding. These results indicate that adrenocortical carcinoma 494 membranes contain beta-adrenergic receptor-binding sites which are not normally present in membranes of adrenal tissue. These ectopic beta-adrenergic receptors presumably confer on the neoplastic tissue the catecholamine sensitivity of its adenylate cyclase.

Adenylyl Cyclases↗
PubMed1977

Regulation of rabbit myometrial alpha adrenergic receptors by estrogen and progesterone.

The effects of estrogen and progesterone on uterine alpha-adrenergic receptors were investigated by direct receptor-binding studies. Immature female rabbits were primed with estrogen by intramuscular injections for 4 days. Other rabbits were primed with progesterone by injections of estrogen for 4 days followed by injections of progesterone for 4 days. The alpha adrenergic antagonist, [3H]dihydroergocryptine, was used to directly assess the number and affinity of alpha adrenergic receptors in membranes derived from estrogen-and progesterone-primed uteri. Membranes from estrogen-primed uteri contained 257 +/- 52 fmol of [3H]dihydroergocryptine-binding sites per mg protein whereas membranes from progesterone-primed uteri contained 83 +/- 11 fmol of of binding sites per mg protein. This reduction of alpha adrenergic receptor-binding sites by progesterone was statistically significant (P less than 0.02). In contrast, no significant difference in the binding site affinity was observed between the estrogen- and progesterone-primed groups. The progesterone-induced decrease in the number of uterine alpha adrenergic receptors provides a potential explanation for the reduced alpha adrenergic contractile response to epinephrine in the progesterone-primed myometrium.

Animals↗
PubMed1976

Identification of alpha-adrenergic receptors in uterine smooth muscle membranes by [3H]dihydroergocryptine binding.

[3H]Dihydroergocryptine, a potent alpha-adrenergic antagonist, was used to label smooth muscle membrane binding sites which have the characteristics expected of alpha-adrenergic receptors. Binding of [3H]dihydroergocryptine to rabbit uterine membranes was rapid and reversible with rate constants of 1.26 X 10(7) M-1 min-1 and 0.034 min-1 for the forward and reverse reactions, respectively. [3H]Dihydroergocryptine binding was of high affinity, with an equilibrium dissociation constant (KD) of 8 to 10 nM. Binding was saturable with 0.14 to 0.17 pmol of [3H]dihydroergocryptine bound/mg of protein at maximal occupancy of the sites. No cooperative interactions among the sites were detected. The specificity of the binding sites for a large number of adrenergic agonists and antagonists was identical with the specificity of alpha-adrenergic responses to these agents. The alpha-adrenergic agonist (-)-epinephrine competed for binding with a KD of 0.23 muM. The order of potencies for several adrenergic agonists in competing for the binding sites was (-)-epinephrine greater than (-)-norepinephrine greater than (-)-phenylephrine greater than (-)-isoproterenol in agreement with their alpha-adrenergic potencies. A series of 19 phenylethylamine adrenergic agonists competed for binding in a manner paralleling their potencies as alpha-adrenergic agonists. alpha-Adrenergic antagonists such as phentolamine (KD = 15 nM) and phenoxybenzamine (KD = 18 nM) potently competed for the binding sites. In contrast, beta-adrenergic antagonists such as propranolol (KD = 27,000 nM) and practolol (KD greater than 10(6) nM) did not have high affinity for the binding sites. A series of ergot alkaloids competed for [3H]dihydroergocryptine binding in a manner which paralleled their potencies as alpha-adrenergic agents. Competition for binding sites by alpha-adrenergic agonists and antagonists was a stereospecific process. The (-)-stereoi somers of epinephrine, norepinephrine, and ergotamine were at least 20- to 50-fold more potent than the corresponding (+)-stereoisomers. Compounds devoid of significant alpha-adrenergic activity, such as pyrocatechol, 3,4-dihydroxymandelic acid, normetanephrine, and D-lysergic acid, did not effectively compete for [3H]dihydroergocryptine binding sites. These rabbit uterine binding sites for [3H]dihydroergocryptine appear to have characteristics indistinguishable from those of the physiologically active alpha-adrenergic receptors.

Animals↗
PubMed1976

Biological activity of agarose-immobilized catecholamines.

Catecholamines substituted to agarose were synthesized in various ways. Norepinephrine and isoproterenol were linked to p-aminobenzamidohexyl agarose by an azo linkage to the catechol ring. Norepinephrine was also couple to hexyl agaros via the amino group, forming an amino, guanidino or amido bond. Biological activity of the immobilized catecholamines was determined by assessing their abilities to interact with adenylate cyclase in several membrane preparations and intact preparations of erythrocytes. In dog heart membranes, stimulation of adenylate cyclase by the catecholamine-gels could be accounted for by leached hormone which had been released from the gels. In frog erythrocyte membranes, leaching was minimal and no significant stimulation of adenylate cyclase was observed. Agarose-immobilized catecholamines, however, competitively inhibited isoproterenol stimulation of adenylate cyclase in these erythrocyte membranes indicating that catecholamines which are bound to agarose interact with the beta-adrenergic receptors as antagonists rather than agonists. When tested on intact frog erythrocytes, agarose immobilzed catecholamines did not increase the intracellular levels of cyclic AMP, although isoproterenol caused as 8-10 fold rise in these levels. Similarly, when tested for antagonist activity in the intact cells the agarose-catecholamines failed to inhibit the stimulation of cyclic AMP caused by isoproterenol. The difference observed in the beta-adrenergic antagonist activity of the agarose-bound catecholamines in membrane preparations and intact cells can be attributed to steric factors which could have prevented the access of the bead-bound ligands with the surface of the cell or to the possibility that receptors might be buried in the membrane matrix.

Adenylyl Cyclases↗
PubMed1976

Negative cooperativity among beta-adrenergic receptors in frog erythrocyte membranes.

(-)-[3H]Dihydroalprenolol, a potent competitive beta-adrenergic antagonist, has been previously documented to bind to the adenylate cyclase-coupled beta-adrenergic receptor sites in mammalian and non-mammalian tissues. Steady state binding of (-)-[3H]dihydroalprenolol to sites in frog erythrocyte membranes, a model system for adenylate cyclase-coupled beta-adrenergic receptors, displays characteristics consistent with negative cooperativity among the beta-adrenergic receptors: Scatchard plots are curvilinear with upward concavity and slopes of Hill plots are consistently less than 1.0. The existence of site-site interactions of the negatively cooperative type were demonstrated directly by the ability of unlabeled (-)-alprenolol to accelerate the dissociation of (-)-[3H]dihydroalprenolol under conditions were no rebinding of radioligand occurred. The dissociation rate of (-)-[3H]dihydroalprenolol alone is directly related to temperature and increases with increases in temperature from 4-37 degrees. (-)-[3H]Dihydroalprenolol dissociation is enhanced by unlabeled (-)-alprenolol at all temperatures studied; however, at 4 degrees, the time required to observe an enhancement of radioligand dissociated is greater than the time required for unlabeled (-)-alprenolol to occupy the empty receptor sites, suggesting that increased rigidity of the biomembrane at 4 degrees may be responsible for the absence of readily observable site-site interactions. The ability of a number of beta-adrenergic agonists and antagonists to induce negative cooperativity among the beta-adrenergic receptors was directly related to their affinity for the receptor sites rather than their intrinsic activity in the adenylate cyclase-coupled beta-adrenergic system. The ability to induce site-site interactions among the beta-adrenergic receptors occurs at physiological concentrations of beta-adrenergic agents, since occupancy of less than 10% of the receptor sites is sufficient to reduce receptor affinity. Changes in pH from 6.5 to 9.0 did not significantly alter the negatively cooperative site-site interactions among the receptor sites. The negatively cooperative phenomenon was also independent of Mg2+, Ca2+, and NaF concentrations in the buffer medium. The presence of guanyl-5'-yl imidodiphosphate, a nonhydrolyzable nucleotide analog which enhances adenylate cyclase stimulation (Vmax) by beta-adrenergic agonists and decreases the concentration of agonist required to half-maximally stimulate adenylate cyclase, did not alter the ability of either agonists or antagonists to induce negatively cooperative site-site interactions among the beta-adrenergic receptors.

Alprenolol↗
PubMed1976

Regulation of beta-adrenergic receptors by guanyl-5'-yl imidodiphosphate and other purine nucleotides.

Guanyl-5'-yl imidodiphosphate (Gpp(NH)p), GTP, and other purine nucleotides selectively decrease the binding affinity of the beta-adrenergic receptors of frog erythrocyte membranes for beta-adrenergic agonists but not antagonists. Shifts in binding affinity were assessed by determining the ability of unlabeled ligands to compete with (-)-[3H]dihydroalprenolol for the membrane-bound receptors. The magnitude of the"right" shift in the binding displacement curve for any of 13 ligands tested was directly related to the intrinsic activity (maximal stimulatory capacity) of that agent for stimulation of the frog erythrocyte membrane adenylate cyclase. Thus, Gpp(NH)p-induced shifts in binding affinity were greatest for full agonists such as isoproterenol, intermediate for partial agonists such as soterenol, and no shifts were observed for antagonists such as propranolol. Shifts in binding affinity were observed only in preparations where agonist binding to the receptors leads to "coupling" of the receptors with adenylate cyclase. In solubilized preparations where the beta-adrenergic receptors and adenylate cyclase are functionally "uncoupled", Gpp(NH)p did not cause right shifts in agonist receptor binding displacement curves. In particulate preparations the Km of Gpp(NH)p for stimulation of adenylate cyclase was identical with that for its effect on beta-adrenergic agonist binding affinity, 1 to 2 muM. Moreover, the ability of several other nucleotides to cause shifts in receptor binding affinity directly paralleled their previously determined affinities for the nucleotide regulatory sites on adenylate cyclase. Gpp(NH)p also shifted agonist dose-response curves for stimulation of adenylate cyclase, but to the left. As with the effects on the receptor binding curves, the effects of Gpp(NH)p on the "apparent affinities" of agonists for enzyme stimulation were directly related to their intrinsic activities. Gpp(NH)p also markedly increased the intrinsic activity of partial agonists. These results appear to indicate that conformational alterations in adenylate cyclase caused by occupation of nucleotide regulatory sites by Gpp(NH)p are capable of inducing alterations in the beta-adrenergic receptors. These receptor alterations are induced only when the receptors are "coupled" to the enzyme by virtue of agonist binding. The nucleotide-altered conformation of the beta-adrenergic receptors is characterized by decreased binding affinity for agonist but increased functional efficacy in stimulating the enzyme.

Adenylyl Cyclases↗
PubMed1976

Adipocyte beta-adrenergic receptors. Identification and subcellular localization by (-)-[3H]dihydroalprenolol binding.

(--)-[3H]Dihydroalprenolol, a potent beta-adrenergic antagonist, was used to identify binding sites which have the characteristics of beta-adrenergic receptors in membranes from rat adipocytes. The subcellular distribution of the (--)-[3H]Dihydroalprenolol binding sites was examined. The binding sites were predominantly in the plasma membrane fraction, consistent with the proposal that the physiologically significant beta-adrenergic receptors are localized in the adipocyte plasma membrane. Binding of (--)-[3H]dihydroalprenolol to unfractionated adipose membranes was saturable with 0.24 pmol bound/mg of protein at saturation. Half-maximal saturation occurred at 15 nM providing an estimate of the equilibrium dissociation constant, KD, for the interaction of (--)-[3H]dihydroalprenolol with its adipocyte receptor. Kinetic analysis of (--)-[3H]dihydroalprenolol binding provided a value of 2.4 X 10(7) M-1 min-1 for the forward bimolecular rate constant, k1. Dissociation of (--)-[3H]dihydroalprenolol was a first order reaction with a rate constant, k2, of 2.94 X 10(-1) min-1. The ratio k2/k1 = 12 nM provides an independent measurement of the KD for the interaction of (--)-[3H]dihydroalprenolol with its receptor which is in good agreement with the values obtained by steady state analysis (12 to 15 nM). Beta-Adrenergic agonists and antagonists competed for the binding sites in unfractionated adipocyte membranes with a typical beta1-adrenergic specificity. The order of potency of agonists was (--)-isoproterenol greater than (--)-norepinephrine congruent to (--)-epinephrine. The beta-adrenergic antagonist, (--)-propranolol, potently competed for the binding sites with a KD of 17 nM. Compounds such as dihydroxyphenylaline, dihydroxymandelic acid, normetanephrine, pyrocatechol, and phentolamine which are structurally related to beta-adrenergic agents, but are devoid of beta-adrenergic physiologicl effects in adipocytes, did not compete for the binding sites. Binding was highly stereospecific, the (+) isomers of adrenergic agonists and antagonists requiring 23- to 330-fold higher concentrations to half-maximally inhibit binding than the corresponding (--) stereoisomers. (--)-[3H]Dihydroalprenolol binding was examined highly enriched plasma membrane, mitochondrial, and microsomal (endoplasmic reticulum) fractions of adipocytes. In the presence of 12 nM (--)-[3H]dihydroalprenolol, the specific activity of binding in the plasma membrane fraction was 5-fold higher than that of the mitochondrial fraction and 8-fold higher than that of the microsomal (endoplasmic reticulum) fraction. The specificity and affinity characteristics of the plasma membrane binding sites were found to be virtually identical with those of the unfractionated adipocyte membranes. The observation that (--)-[3H]dihydroalprenolol binding sites are predominantly localized in the plasma membrane fraction suggests the potential usefulness of this ligand as a marker for adipocyte plasma membranes.

Adenylyl Cyclases↗
PubMed1976

Alpha-adrenergic receptor identification by (3H)dihydroergocryptine binding.

A radioactively labeled alpha-adrenergic antagonist, [3H]dihydroergocryptine, binds specifically to a site on rabbit uterine membranes. Binding is rapid, reaching equilibrium in less than 17 minutes at 25 degrees C. Adrenergic agonists compete for this binding site with an order of affinities identical to the pharmacological potency order of these agents as alpha-adrenergic agonists (epinephrine greater than norepinephrine greater than isoprotereonl). The (-) stereoisomers of epinephrine and norepinephrine are 30 times more potent in competing for the site than the corresponding (+) stereoisomers. alpha-Adrenergic antagonists, such as phentolamine and phenoxybenzamine, potently compete for the binding sites while the beta-adrenergic antagonist propranolol does not. Structural analogs of catecholamines that are devoid of alpha-adrenergic physiological activity do not compete for [3H]dihydroergocryptine binding sites. These data suggest that alpha-adrenergic receptors can be directly identified and studied by [3H]dihydroergocryptine binding.

Adrenergic alpha-Agonists↗