Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P61278 (somatostatin)
 22,083 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We characterized structurally the receptors for somatostatin in rat cerebral cortex by affinity labeling with [125I-Tyr1] somatostatin. [125I-Tyr1] somatostatin was cross-linked to cerebrocortical membranes using photoreactive cross-linker: N-5-azido-2-nitrobenzoyloxy-succinimide. Analysis by autoradiography revealed a broad band centered at Mr = 72,000 in the presence or absence of dithiothreitol. Affinity labeling of and specific [125I-Tyr1] somatostatin binding to cerebrocortical membranes were decreased similarly by adding unlabeled somatostatin or nonhydrolyzable guanine nucleotide analogue, guanyl-5'-yl imidodiphosphate, in a dose dependent manner. The pretreatment of cerebrocortical membranes with islet activating protein resulted in a decrease in subsequent affinity labeling of the protein. The cross-linked protein could be solubilized with Zwittergent 3-12 and poorly with digitonin, triton X-100 and NP-40. When exposed to agarose-coupled lectins, the solubilized labeled protein was absorbed to wheat germ agglutinin, partially to ricin communis-II, and not to concanavalin A or lentil lectin. The Mr = 72,000 protein bound to wheat germ agglutinin-agarose was eluted with not only N,N',N"-triacetylchitotriose but also N-acetylglucosamine. These results suggest that somatostatin receptors on cerebrocortical membranes are a monomeric glycoprotein with a Mr = 70,000 containing no disulfide-linked binding subunit, which is coupled to islet activating protein-sensitive guanine nucleotide regulatory protein.
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PMID:[Structural characterization of the somatostatin receptors on rat cerebrocortical membranes]. 198 Aug 94

Somatostatin receptors of plasma membranes from beta cells of hamster insulinoma were covalently labelled with 125I-[Leu8,D-Trp22,Tyr25]somatostatin-28 (125I-somatostatin-28) and solubilized with the non-denaturing detergent Triton X-100. Analysis by SDS/PAGE and autoradiography revealed three specific 125I-somatostatin-28 receptor complexes with similar molecular masses (228 kDa, 128 kDa and 45 kDa) to those previously identified [Cotroneo, P., Marie, J.-C. & Rosselin, G. (1988) Eur. J. Biochem. 174, 219-224]. The major labelled complex (128 kDa) was adsorbed to a wheat-germ-agglutinin agarose column and eluted by N-acetylglucosamine. Also, the binding of 125I-somatostatin-28 to plasma membranes was specifically inhibited by the GTP analog, guanosine-5'-O-(3-thiotriphosphate) (GTP[S]) in a dose-dependent manner. Furthermore, when somatostatin-28 receptors were solubilized by Triton X-100 as a reversible complex with 125I-somatostatin-28, GTP[S] specifically dissociated the bound ligand to a larger extent from the soluble receptors than from the plasma-membrane-embedded receptors, the radioactivity remaining bound after 15 min at 37 degrees C being 30% and 83% respectively. After pertussis-toxin-induced [32P]ADP-ribosylation of pancreatic membranes, a 41-kDa [32P]ADP-ribose-labelled inhibitory guanine nucleotide binding protein coeluted with the 128-kDa and 45-kDa receptor complexes. The labelling of both receptor proteins was sensitive to GTP[S]. The labelling of the 228-kDa band was inconsistent. These results support the conclusion that beta cell somatostatin receptors can be solubilized as proteins of 128 kDa and 45 kDa. The major labeled species corresponds to the 128-kDa band and is a glycoprotein. The pancreatic membrane contains a 41-kDa GTP-binding protein that can complex with somatostatin receptors.
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PMID:Solubilization of somatostatin receptors in hamster pancreatic beta cells. Characterization as a glycoprotein interacting with a GTP-binding protein. 257 68

The receptor for somatostatin present in rat pancreatic plasma membranes was characterized by affinity labeling with [125I-Tyr11]somatostatin utilizing three different heterobifunctional cross-linking agents: N-5-azido-2-nitrobenzoyloxy-succinimide, N-succinimidyl 6-(4-azido 2'-nitrophenylamine)hexanoate, and N-hydroxysuccinimidyl 4-azido-benzoate. Analysis by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and autoradiography revealed a broad band of Mr = 92,000 when any of the three cross-linkers was used; N-succinimidyl 6-(4-azido 2'-nitrophenylamine), however, was most efficient. Labeling of the Mr = 92,000 protein band was not affected by reducing agents but was sensitive to somatostatin and guanine nucleotides, particularly GTP gamma S, at concentrations which reduced binding to the receptor. The affinity-labeled protein could be solubilized completely with Zwittergent 3-12, partially with Triton X-100 and 3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonic acid, and poorly with Zwittergent 3-08 and digitonin. When exposed to agarose-coupled lectins, the detergent solubilized, labeled Mr = 92,000 protein was completely adsorbed to wheat germ agglutinin, partially to ricin communis II, and not at all to concanavalin A or lotus or lentil lectin. The Mr = 92,000 protein bound to wheat germ agglutinin-agarose was not eluted by N-acetylglucosamine but was by triacetylchitotriose, providing a considerable purification of the somatostatin receptor. These data allow us to conclude that the somatostatin receptor is a monomeric glycoprotein with an Mr = 90,000 binding subunit which probably contains a polymeric arrangement of N-acetylglucosamine residues.
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PMID:Characterization of covalently cross-linked pancreatic somatostatin receptors. 287 90

To structurally characterize the somatostatin receptor in the anterior pituitary, the chemical cross-linking reagent N-5-azido-nitrobenzoyloxysuccinimide was used to attach covalently [125I-Tyr11]somatostatin-14 to its receptor in pituitary membranes. Rat anterior pituitary membranes were incubated with [125I-Tyr11]somatostatin-14, washed, and then treated with 100 microM cross-linker, which was activated by exposure to UV light. Gel electrophoresis followed by autoradiography revealed a broad band centered at 88,000 mol wt. The appearance of this band was unaffected by dithiothreitol. Competitive inhibition of binding by unlabeled somatostatin resulted in a parallel inhibition of labeling of the 88,000 mol wt protein. The addition of guanine nucleotides in concentrations that inhibit binding similarly inhibited cross-linking. The cross-linked membranes were solubilized in Zwittergent 3-12, a nondenaturing detergent, and the glycosylation pattern of the labeled protein was investigated by incubation with various lectins coupled to agarose. The cross-linked protein was selectively adsorbed by wheat germ agglutinin, and this interaction was blocked by the addition of N,N',N"-triacetylchitotriose, indicating that the rat anterior pituitary somatostatin receptor is a glycoprotein containing polymeric beta-1-4 linked N-acetylglucosamine groups. The results of this study show that the rat anterior pituitary somatostatin receptor is a glycoprotein of 88,000 mol wt containing no disulfide-linked subunits.
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PMID:Structural characterization of the somatostatin receptor in rat anterior pituitary membranes. 288 81

Somatostatin binding and cross-linking to its receptors on rat cerebrocortical membranes were characterized with [125I-Tyr1]somatostatin-14 and [125I-Leu8, D-Trp22, Tyr25]somatostatin-28. When [125I-Tyr1]somatostatin-14 was cross-linked to its receptors with the photoreactive cross-linker, N-(5-azido-2-nitrobenzoyloxy)succinimide, the hormone was specifically associated with a Mr = 72,000 protein band in the presence or absence of reducing agents. Affinity labeling of the Mr = 72,000 protein band was decreased with increasing concentrations of unlabeled somatostatin-14 and nonhydrolyzable guanine nucleotide analog, guanyl-5'-yl imidodiphosphate (Gpp(NH)p). Pretreatment of cerebrocortical membranes with islet-activating protein resulted in a decrease in subsequent labeled somatostatin-14 binding and affinity-labeling of the protein and abolished an inhibitory effect of somatostatin-14 on vasoactive intestinal peptide-stimulated increase in adenylate cyclase activity. When the affinity-labeled protein was solubilized with Zwittergent 3-12 and adsorbed to wheat germ agglutinin-agarose, it was eluted by N-acetylglucosamine. [125I-Leu8, D-Trp22, Tyr25]somatostatin-28 cross-linking to cerebrocortical and pancreatic membranes with the same photoreactive agent revealed specifically labeled protein bands of a Mr = 74,000 in cerebrocortical membranes and a Mr = 94,000 in pancreatic membranes, respectively. These results suggest that: 1) somatostatin receptor on cerebrocortical membranes is a monomeric glycoprotein with a Mr = 70,000 binding subunit, coupled to guanine nucleotide regulatory protein, and 2) the Mr = 70,000 protein may be a common receptor for somatostatin-28 and somatostatin-14 and is distinct from a common pancreatic type receptor.
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PMID:Somatostatin receptors on rat cerebrocortical membranes. Structural characterization of somatostatin-14 and somatostatin-28 receptors and comparison with pancreatic type receptors. 290 82

Results from recent studies have indicated that pancreatic islet prohormone converting enzymes are membrane-associated in islet microsomes and secretory granules. This observation, along with the demonstration that proglucagon is topologically segregated to the periphery within alpha cell secretory granules in several species, led us to investigate the possibility that newly synthesized islet prohormones might be associated with intracellular membranes. Anglerfish islets were incubated with [3H]tryptophan and [14C]isoleucine for 3 h, then fractionated by differential and density gradient centrifugation. Microsome (M) and secretory granule (SG) fractions were halved, sedimented, and resuspended in the presence or absence of dissociative reagents. After membrane lysis by repeated freezing and thawing, the membranous and soluble components were separated by centrifugation. Extracts of supernatants and pellets were chromatographed by gel filtration; fractions were collected and counted. A high proportion (77-79%) of the newly synthesized proinsulin and insulin was associated with both M and SG membranes. Most of the newly synthesized proglucagons and prosomatostatins (12,000-mol-wt precursors) were also membrane-associated (86-88%) in M and SG. In contrast, glucagon- and somatostatin-related peptides exhibited much less membrane-association in SG (24-31%). Bacitracin, bovine serum albumin EDTA, RNAse, alpha-methylmannoside, N-acetylglucosamine, and dithiodipyridine had no effect on prohormone association with membranes. However, high salt (1 M KCl) significantly reduced membrane-association of prohormones. Binding of labeled prohormones to SG membranes from unlabeled tissue increased with incubation time and was inhibited by unlabeled prohormones. The pH optimum for prohormone binding to both M and SG membranes was 5.2. It is suggested that association of newly synthesized prohormones with intracellular membranes could be related to the facilitation of proteolytic processing of prohormones and/or transport from their site of synthesis to the secretory granules.
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PMID:Association of newly synthesized islet prohormones with intracellular membranes. 614 27

Radiolabeled somatostatin analogues have been successfully used for targeted radiotherapy and for imaging of somatostatin receptor (sst1-5)-positive tumors. Nevertheless, these analogues are subject to improving their tumor-to-nontarget ratio to enhance their diagnostic or therapeutic properties, preventing nephrotoxicity. In order to understand the influence of lipophilicity and charge on the pharmacokinetic profile of [1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA)]-somatostatin-based radioligands such as [DOTA,1-Nal3]-octreotide (DOTA-NOC), different spacers (X) based on 8-amino-3,6-dioxaoctanoic acid (PEG2), 15-amino-4,7,10,13-tetraoxapentadecanoic acid (PEG4), N-acetyl glucosamine (GlcNAc), triglycine, beta-alanine, aspartic acid, and lysine were introduced between the chelator DOTA and the peptide NOC. All DOTA-X-NOC conjugates were synthesized by Fmoc solid-phase synthesis. The partition coefficient (log D) at pH = 7.4 indicated that higher hydrophilicity than [111In-DOTA]-NOC was achieved with the introduction of the mentioned spacers, except with triglycine and beta-alanine. The high affinity of [InIII-DOTA]-NOC for human sst2 (hsst2) was preserved with the structural modifications, while an overall drop for hsst3 affinity was observed, except in the case of [InIII-DOTA]-beta-Ala-NOC. The new conjugates preserved the good affinity for hsst5, except for [InIII-DOTA]-Asn(GlcNAc)-NOC, which showed decreased affinity. A significant 1.2-fold improvement in the specific internalization rate in AR4-2J rat pancreatic tumor cells (sst2 receptor expression) at 4 h was achieved with the introduction of Asp as a spacer in the parent compound. In sst3-expressing HEK cells, the specific internalization rate at 4 h for [111In-DOTA]-NOC (13.1% +/- 0.3%) was maintained with [111In-DOTA]-beta-Ala-NOC (14.0% +/- 1.8%), but the remaining derivatives showed <2% specific internalization. Biodistribution studies were performed with Lewis rats bearing the AR4-2J rat pancreatic tumor. In comparison to [111In-DOTA]-NOC (2.96% +/- 0.48% IA/g), the specific uptake in the tumor at 4 h p.i. was significantly improved for the 111In-labeled sugar analogue (4.17% +/- 0.46% IA/g), which among all the new derivatives presented the best tumor-to-kidney ratio (1.9).
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PMID:Influence of different spacers on the biological profile of a DOTA-somatostatin analogue. 1722 60