Acetylcholinesterase and Butyrylcholinesterase Expression in Adult Rabbit Tissues and during Development

Abstract

A large cDNA fragment covering the complete sequence of the mature catalytic subunit of rabbit acetylcholinesterase (AChE, EC 3.1.1.7.) has been cloned and sequenced. This sequence was compared to that of rabbit butyrylcholinesterase (BChE, EC 3.1.1.8.; Jbilo, O. & Chatonnet, A., 1990, Nucleic Acids Res. 18, 3990). Amino acids sequences of AChE and BChE had 51% identity. They both possessed a choline binding site W(84), a catalytic triad S(200)-H(440)-E(327) and six cysteine residues (67–94; 254–265; 402–521) in conserved sequence positions to those that form three intrachain disulfide bonds in all cholinesterases (by convention, numbering of amino acids is that of Torpedo AChE). Rabbit AChE had a larger number of aromatic residues lining the active site gorge than rabbit BChE (14 versus 8) and a smaller number of potential N-glycosylation sites (3 versus 8). Both catalytic subunits had a hydrophilic C-terminus (catalytic subunits of type T) characterized by a regular disposition of 7 aromatic residues in conserved position to 7 residues found in T subunits of Torpedo AChE. Expression of acetycholinesterase and butyrylcholinesterase genes (ACHE and BCHE) was studied in rabbit tissues and during development by a correlation of Northern blot analysis and enzymatic activities. The correlation was rendered difficult by the presence of an eserine-resistant esterase active on butyrylthiocholine in serum, liver and lung. This enzyme was characterized. When the contribution of this carboxylesterase was taken into account, brain was found as the richest source of BChE followed by lung and heart. Rabbit liver had a very low content of BChE that correlated with the low BChE activity in plasma. During development BCHE transcripts were detected as early as day 10 postcoitum whereas ACHE transcripts appeared only on day 12.