th  - 1987 - 51st ENC Conference

MF41
ACETYLCHOLINE RECEPTOR --AGONIST BINDING.
RESULTS FROM SELECTIVE RELAXATION NMR EXPERIMENTS.
Ronald W. Behling °, Tetsuo Yarnane, Gil Navon t,
Michael J. Samrnon, and Lynn W. Jelinski
AT~T Bell Laboratories Murray Hill, New Jersey 07974
t Tel-Aviv University, Israel
Selective proton NMR relaxation mea-~urements were used with nicotine
titrations to obtain relative binding constants for nicotine, acetylcholine,
muscarine, and carbamylcholine binding to purified acetylcholine receptors from
Torpedo californica. The results show (1) that the binding constants are in the
order acetylcholine > nicotine > carbamyl choline > muscarine; (2) that
selective and non-selective NMR measurements provide a rapid and direct
method for monitoring both the specific and non-specific binding of agonists to
these receptors; (3) that a-bungarotoxin can be used to distinguish between
specific and non-specific binding to the receptor; (4) that the receptor-substrate
interaction produces a large change in the selective relaxation time of the
agonists even at concentrations 100x greater than that of the receptor. This
latter observation means that these measurements provide a rapid way to
measure drug binding when only small amounts of receptor are available, and
that they may be useful for determining the conformation of the small ligand in
its bound state.