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Iodinated photoreactive vasopressin antagonists: labelling of hepatic vasopressin receptor subunits

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Fahrenholz,  Falk
Department of Physical Chemistry, Max Planck Institute of Biophysics, Max Planck Society;

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Kojro,  Elzbieta
Department of Physical Chemistry, Max Planck Institute of Biophysics, Max Planck Society;

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Müller,  Michael
Department of Physical Chemistry, Max Planck Institute of Biophysics, Max Planck Society;

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Boer,  Rainer
Department of Physical Chemistry, Max Planck Institute of Biophysics, Max Planck Society;

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Löhr,  Reinhold
Department of Physical Chemistry, Max Planck Institute of Biophysics, Max Planck Society;

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Citation

Fahrenholz, F., Kojro, E., Müller, M., Boer, R., Löhr, R., & Grzonka, Z. (1986). Iodinated photoreactive vasopressin antagonists: labelling of hepatic vasopressin receptor subunits. European Journal of Biochemistry, 161(2), 321-328. doi:10.1111/j.1432-1033.1986.tb10450.x.


Cite as: http://hdl.handle.net/21.11116/0000-0007-A690-A
Abstract
To identify and characterize V1 vasopressin receptors, photoreactive antagonists of the glycogenolytic and vasoconstrictor activity of vasopressin have been synthesized. The following analogues with 3‐mercapto‐ 3,3‐cyclopentamethylene‐propionic acid (Mca) and N‐methylalanine (MeAla) in position 1 and 7 of vasopressin (VP) were effective V1 antagonists: [Mca1,D‐Tyr2,MeAla7,Lys8]VP (l), [Mca1,MeAla7,Arg8,Lys9]VP (2), [Mca1,MeAla7,Arg8,d‐Lys9]VP (3). Introduction of the photoreactive 4‐azidophenylamidino group into the side‐ chain of Lyss8 in analogue 1 or into Lys9 in analogues 2 and 3 increased the potency (for analogue 1 a tenfold increase in the antiglycogenolytic effect and a fivefold increase in the antivasopressor effect) and binding affinity for the rat hepatic V1 receptor. Mono‐iodination at Tyr2 with 125I resulted in photoreactive antagonists of high specific radioactivity, which had roughly the same binding affinity as vasopressin for the rat hepatic V1 receptor (Kd= 0.9—1.8 nM). In photoaffinity labelling experiments with purified rat liver membranes, containing 2–3 pmol V1 receptor/ mg protein, the analogues labelled specifically two proteins with the relative molecular masses (Mr) of 30000 and 38 000. These results and the results of a recent study using 3H‐labelled photoreactive vasopressin agonists [Boer, R. and Fahrenholz, F. (1985) J. Bid. Chem. 260, 15051 ‐ 150541 provide evidence that both vasopressin agonists and antagonists can interact with the same two subunits of the heterodimeric hepatic V1 receptor. Furthermore the radioiodinated photoreactive V1 antagonists should be helpful to identify V1 receptor proteins in membranes of other cell types.