Reaction of [3H]meproadifen mustard with membrane-bound Torpedo acetylcholine receptor.

The Torpedo nicotinic acetylcholine receptor (AChR) contains a binding site for aromatic amine noncompetitive antagonists that is distinct from the binding site for agonists and competitive antagonists. To characterize the location and function of this allosteric antagonist site, an alkylating analog of meproadifen has been synthesized, 2-(chloroethylmethylamino)-ethyl-2, 2-diphenylpentanoate HCl (meproadifen mustard). Reaction of [3H]meproadifen mustard with AChR-rich membrane suspensions resulted in specific incorporation of label predominantly into the AChR alpha-subunit with minor incorporation into the beta-subunit.

Location of ligand-binding sites on the nicotinic acetylcholine receptor alpha-subunit.

The portions of the Torpedo californica nicotinic acetylcholine receptor (AChR) alpha-subunit that contribute to the allosteric antagonist-binding site and to the agonist-binding site have been localized by affinity labeling and proteolytic mapping. [3H]Meproadifen mustard was employed as an affinity label for the allosteric antagonist-binding site and [3H]tubocurare as a photoaffinity label for the agonist-binding site. Both labels were found in a 20-kDa proteolytic fragment generated from the AChR alpha-subunit by Staphylococcus aureus V8 protease.

Phytochrome-mediated uptake of calcium in Mougeotia cells.

Ca(2+) is proposed to function as a messenger in such phytochrome-mediated responses as localized cell growth, intracellular movements, and control of plasma membrane properties. To test this hypothesis, the uptake of Ca(2+) in irradiated and non-irradiated regions of individual threads of the green alga Mougeotia was studied with the aid of (45)Ca(2+) and low temperature autoradiography: 10-20 cells within 40-60 cell-long threads were irradiated for up to 1 min, transferred to darkness for 3 to 10 min, submersed in a radioactive medium for 1 min, washed in an unlabelled medium for 30 min, and then autoradiographed at-80° C for several days.The autoradiographs show that those cells which had been pre-irradiated with red light did take up 2-10 times more Ca(2+) than the adjacent non-irradiated cells of the same thread.