Hydrophobic labeling of the membrane binding domain of acetylcholinesterase from Torpedo marmorata

Membrane-bound acetylcholinesterase (AChE) from the electric organ of Torpedo marmorata was labeled with the hydrophobic photoactivatable reagent 3-trifluoromethyl-3-(m-[125I]iodophenyl) diazirine ( [125I]TID). Labeling with [125I]TID was restricted to the membranous polypeptide segment of AChE as shown upon conversion of the amphiphilic form to the hydrophilic one by limited digestion with proteinase K. The labeled membranous segment, which has an Mr of approx. 3000 was isolated by gel filtration on Sephadex LH-60 in ethanol/formic acid.