title: On the location of active serines of membrane acetylcholinesterase studied by the ESR method.
abstract: 1. An attempt was made to find out the causes of the discrepancy between the ESR spectra of membrane acetylcholinesterase (EC 3.1.1.7) obtained by Morrisett and co-workers and those obtained by the present authors. 2. In order to see whether the discrepancy was due to the different spin-labeling procedures, the same membrane acetylcholinesterase preparations were spin-labeled with the same compound, using the two different spin-labeling procedures. The enzyme activity was determined with pH-static titration and the ESR spectra recorded. 3. It was found that after spin-labeling according to Morrisett and co-workers, there were from 10-100 times more spin-label molecules bound to the enzyme preparations than there were active serines in them. 4. Using the method of Morrisett and co-workers, the majority of spin-label molecules was found to be bound to sites outside the active serines whereas the spin-labeling procedures of the present authors proved to be selective for active serines; the discrepancy in ESR spectra is explained.
mesh_terms: D000110:Acetylcholinesterase; D000818:Animals; D001665:Binding Sites; D002417:Cattle; D004557:Electric Organ / Q000201:enzymology*; D004578:Electron Spin Resonance Spectroscopy; D004912:Erythrocytes / Q000201:enzymology; D005399:Fishes; D008566:Membranes / Q000201:enzymology*; D011485:Protein Binding; D012694:Serine; D013113:Spin Labels
chemical_list: D013113:Spin Labels; D012694:Serine; D000110:Acetylcholinesterase