Opiate receptors.

An arylazide enkephalin derivative, [D-Ala2,Met5]enkephalin-Tyr-N-(2-nitro-4-azidophenyl) ethylenediamine (ETN), has been synthesized. In the dark, it inhibited the binding of [3H]enkephalinamide to enkephalin receptor-rich NG-108 cell membranes with an I50 = 2.2 X 10(-8) M or KI = 7 X 10(-9) M, assuming competitive inhibition. Photolysis of membranes in the presence of ETN caused irreversible inactivation of the enkephalin receptor, but inactivation was prevented by the addition of enkephalin, the half-effective concentration being 3 x 10(-9) M. ETN appears to be an effective photoaffinity label for the enkephalin receptor.

Affinity Labels↗

PubMed1979

Use of a GTP photoaffinity probe to resolve aspects of the mechanism of tubulin polymerization.

8-Azidoguanosine 5'-triphosphate (8-N3GTP) was used in a photoactivatable probe to examine the role of GTP in microtubule assembly. 8-N3GTP was able to substitute for GTP in the promotion of tubulin polymerization and was hydrolyzed at 37 degrees C in the presence or absence of colchicine or calcium. Photolysis of the analog in the presence of microtubular protein resulted in its covalent incorporation onto a GTP-specific site of the beta monomer. The efficiency of this incorporation was different when 8-N3GDP (which does not affect polymerization) was used in place of 8-N3GTP, implying a different orientation of the nucleoside diphosphate within the receptor site. During microtubule assembly, 8-N3GTP was hydrolyzed in situ at the tubulin-GTP exchangeable site in a process that was dependent upon polymerization. The use of [beta, gamma-32P]8-N3GTP and [gamma-32P]8-N3GTP indicated that this hydrolysis occurred concurrently with polymerization and that only nucleoside diphosphate remained bound to the polymerized tubulin.

Affinity Labels↗