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At least 973 records · Page 54Linked to original sources
PubMed1983

Solubility of phenothiazines in red blood cell membranes as evidenced by photoaffinity labeling.

Radioactively labeled 7-azido-fluphenazine and 7-azido-triflupromazine methiodide have been synthesized and their binding to membranes of intact red blood cells and to ghosts was compared after irradiation. The results indicated that tertiary phenothiazines react with integral membrane components. We conclude from the results that amphiphilic substances solubilize in biological membranes. This is in contradiction to the proposal that these compounds are excluded from the hydrophobic core of biological membranes (Conrad & Singer (1979) Proc.Natl.Acad.Sci.U.S.A. 76, 5202-5206 and (1981) Biochemistry 20, 808-818).

Affinity Labels↗
PubMed1984

Photoaffinity labeling of gonadotropin releasing hormone receptors in control and desensitized pituitary cells.

Gonadotropin releasing hormone (GnRH), preincubated with cultured rat pituitary cells, induced down regulation of GnRH receptors in a time- and dose-dependent manner. The specific binding was inhibited by 50% after 30 min and maximal inhibition (70%) was obtained after 75 min preincubation with 1 microM GnRH. Preincubation of the cells for 2 h with 10 nM GnRH inhibited the specific binding by 20%, reaching a plateau of 70% inhibition with 0.1 microM GnRH. Concomitantly, exposure of the cells to GnRH caused a time- and dose-dependent desensitization of LH release. The responsiveness of the desensitized cells was not parallel to the binding capacity and was inhibited to a greater extent (93%). Photoactivation of GnRH receptors with iodinated [azidobenzoyl-D-Lys6]GnRH in control and desensitized cells resulted in the identification of a single specific band with the same apparent molecular weight of 60K daltons. These results indicate that structural alterations of GnRH receptors are not associated with GnRH-induced desensitization. Therefore, desensitization may involve conformational changes in the receptor or more likely a post-receptor mechanism.

Affinity Labels↗
PubMed1984

[1,6-alpha-aminosuberic acid,3-(p-azidophenylalanine), 8-arginine] vasopressin as a photoaffinity label for renal vasopressin receptors: an evaluation.

The photoreactive analog of vasopressin [1,6-alpha-aminosuberic acid,3-(p-azidophenylalanine), 8-arginine]vasopressin was labeled with tritium (specific radioactivity: 39 Ci/mmole). In the absence of UV-light, the tritium-labeled ligand retained a high binding affinity to the vasopressin receptor in plasma membranes from bovine kidney inner medulla (apparent dissociation constant KD: 1.4 X 10(-8) M). Renal plasma membranes were irradiated under conditions of a high ratio of specific versus non-specific binding of the reactive ligand. Sodium dodecyl sulfate gel electrophoresis after solubilization and reduction demonstrated the preferential labeling of a polypeptide with an apparent molecular weight of Mr = 32 000. A comparison with stained gels revealed that this protein is a minor constituent of the bovine kidney membrane. Our results suggest the 32 000-dalton polypeptide is either a component of the vasopressin receptor or that it is located in the immediate vicinity of the vasopressin binding protein.

Affinity Labels↗
PubMed1985

Specific photoaffinity labelling of inhibitory adenosine receptors.

N6(L-phenylisopropyl)adenosine (L-PIA) and N6(3-iodo-4-azido benzyl)-adenosine (IAzBA) inhibit the adenylate cyclase activity in synaptic membranes of chick cerebellum via Ri adenosine receptors. [3H]L-PIA and [125I]AzBA bind to these membranes with Kd values of approximately 1 nM and Bmax values of approximately 1000 fmol/mg protein. Photolysis of [125I]AzBA bound to synaptic membranes results in the specific incorporation of radioactivity into a protein with Mr = 36,000. This photoincorporation is blocked by simultaneous exposure to L-PIA, theophylline, an adenosine receptor antagonist, or Gpp(NH)p, but not by cytosine, suggesting that the 36,000 dalton protein is the Ri adenosine receptor or a subunit of the receptor that contains the adenosine binding site.

Adenosine↗
PubMed1988

Structural analysis of the calcium channel by photoaffinity labelling and limited proteolysis.

The L-type calcium channel of rabbit skeletal muscle triads, purified from digitonin extracts, was photolabelled with the dihydropyridine (+)[3H]PN 200-110. This photolabelled form was then subjected to limited proteolysis with papain and staphylococcus V-8 protease and analyzed by polyacrylamide gel electrophoresis. In the absence of proteolysis, the photolabelled channel was represented by a single protein with an apparent molecular weight of 160 kDa in the presence or absence of reducing agents. Following proteolysis, numerous photoadducts were observed with smaller molecular weights. The V-8 protease digestion pattern indicated that photoinsertion occurred in at least two distinct domains of 33 and 28 kDa. Papain digests were more extensive, generating smaller fragments of 28 and ca. 10 kDa. The results suggest that at least two distinct regions of the calcium channel interface at or near the dihydropyridine binding site, and that the binding site for these calcium antagonists resides within the channel proper, thereby modulating calcium influx.

Affinity Labels↗