Amphiphilic and hydrophilic forms of acetyl‐ and butyrylcholinesterase in human brain

Abstract

Human brain acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) were sequentially extracted, first with a Tris‐saline buffer (S₁) and then with 1% (w/v) Triton X‐100 (S₂). About 20 and 30% of the AChE and BuChE activities were recovered in S₁ and most of the remaining enzymes in S₂. Main molecular forms of about 10.5 S and 12.0 S, G₄ forms of AChE and BuChE, and smaller amounts of 4.5 S and 5.5 S forms, G₁ species of AChE and BuChE, were measured in S₁. Application of Triton X‐114 phase partitioning and affinity chromatography on phenyl‐agarose to S₁ revealed that 25% of the AChE and none of the BuChE molecules displayed amphiphilic properties. Analysis of the enzyme activity retained by the phenyl‐agarose showed that G₁ AChE constituted the bulk of the amphiphilic molecules released without detergent. Main G₄ forms of AChE and BuChE were found in the S₂ extract. Eighty and 45% of the AChE and BuChE activities in S₂ were measured in the detergent‐rich phase by Triton X‐114 phase partitioning. Thus, most of the AChE and about half of the BuChE molecules in S₂ displayed amphiphilic properties. The main peak of BuChE, a 12.0 S form in gradients made with Triton X‐100, splits into two peaks of 9.5 S and 12.5 S in Brij 96‐containing gradients. This suggests that hydrophilic G₄ BuChE forms are predominant in S₁ and that hydrophilic and amphiphilic isoforms coexist in S₂.