TRP279 IS INVOLVED IN THE BINDING OF QUATERNARY AMMONIUM AT THE PERIPHERAL SITE OF TORPEDO-MARMORATA ACETYLCHOLINESTERASE

Specific photoaffinity labelling of purified acetylcholinesterase from Torpedo marmorata by p-N,N-[H-3]dimethylamino benzenediazonium and p- N,N-[H-3]dibutylamino benzenediazonium derivatives was demonstrated. T his occured at the active site of the enzyme for lower concentrations of the probes and at the peripheral ammonium binding site for higher c oncentrations. The affinities and the rate constants of alkylation for each probe on both sites have been established. Specific labelling at the peripheral site of the enzyme with both probes allowed the identi fication of radiolabelled peptides having the common sequence K270PQEL IDVEW. The radioactivity was always associated with the residue Trp279 indicating the preferential ammonium complexation with this aromatic residue.