Bovine Nucleus Caudatus Acetylcholinesterase: Active Site Determination and Investigation of a Dimeric Form Obtained by Selective Proteolysis

Abstract

The number of catalytic subunits of purified bovine nucleus caudatus acetylcholinesterase (EC 3.1.1.7) was determined by active site labeling with [3H]diisopropyl fluorophosphate ([3H]DFP). The 10.5 S [Svedberg unit] 16 S, and 20 S forms were estimated to contain 2, 4 and 6 active sites, respecitvely, per molecule. A 4.8 S form, which showed a weak amphiphile-dependent activity behavior, was obtained by selective proteolytic digestion with pronase. The inability of the purified 4.8 S form to aggregate after detergent removal, and the molecular mass in the range of 130-165 kD [k Daltons] under nondenaturating conditions, indicate that this form is a dimeric form, lacking those hydrophobic regions responsible for aggregation.