title: Active-site determinations on forms of mammalian brain and eel acetylcholinesterase.
abstract: Three forms of brain acetylcholinesterase were purified from bovine caudate-nucleus tissue and determined by calibrated gel filtration to have mol.wts. of approx. 120 000 (C), 230 000 (B) and 330 000 (A). [3H]Di-isopropyl phosphorofluoridate (isopropyl moiety labelled) was purified from commercial preparations and its concentration estimated by an enzyme-titration procedure. Brain acetylcholinesterase preparations and enzyme from eel electric tissue were allowed to react with [3H]di-isopropyl phosphorofluridate in phosphate buffer until enzyme activity was inhibited by 98%. Excess of [3H]di-isopropyl phosphorofluoridate that had not reacted was separated from the labelled enzyme protein by gel filtration, or by vacuum filtration or by extensive dialysis. The specificity of active-site labelling was confirmed by use of the enzyme reactivator, pyridine 2-aldoxime. The forms of brain acetylcholinesterase were calculted to contain approximately two (C) four (B) and six (A) active sites per molecule respectively. Acetylcholinesterase (mol.wt. 250 000) from electric-eel tissue was estimated to contain two active sites per molecule. Gradient-gel electrophoresis was used to confirm the estimation of molecular weights of brain acetylcholinesterase forms made by gel filtration. Under the conditions of electrophoresis acetylcholinesterase form A was stable, but form B was converted into a species of approx. 120 000 mol. wt. Similarly, form C of the brain enzyme was converted into a 60 000-mol.wt. form during electrophoresis. These results are in general accord with the suggestion that the multiple forms of brain acetylcholinesterase may be related to the aggregation of a single low-molecular-weight species.
mesh_terms: D000110:Acetylcholinesterase / Q000032:analysis*; D000818:Animals; D001665:Binding Sites; D001921:Brain / Q000201:enzymology*; D002417:Cattle; D002850:Chromatography, Gel; D004591:Electrophoresis, Polyacrylamide Gel; D004593:Electrophorus / Q000378:metabolism*; D007531:Isoflurophate / Q000032:analysis; D008970:Molecular Weight; D011725:Pyridines / Q000494:pharmacology
chemical_list: D011725:Pyridines; D007531:Isoflurophate; D000110:Acetylcholinesterase