Photoaffinity labeling of acetylcholine receptor in millisecond time scale

Photoaffinity labeling of acetylcholine receptors can be performed with a time resolution allowing to discriminate reaction sites within the receptor protein in its different functional states. This is achieved by a combination of a stopped-flow apparatus with a high energy pulse laser. The photoaffinity label used is the lipophilic cation [3H]TPMP+ which has been shown to be a non-competitive antagonist and a specific ion channel blocker. AChR in its resting (channel closed) and active (channel open) state incorporates the label mainly into the alpha-polypeptide chain of the receptor. Only several hundred milliseconds after mixing AChR with agonist labeling of delta-chains becomes significant.