Abstract
Acetylcholinesterase (AChE) was recently purified and cloned from maize, which is the first direct evidence of the plant AChE. Purified AChE was 88-kDa homodimers consisting of 42-44kDa polypeptides. The full-length cDNA of maize AChE gene is 1471 nucleotides, encoding a protein having 394 residues, including a signal peptide. In this study, enzymatic characterization of maize AChE was compared with AChE from Macroptilium atropurpureum and electric eel as representative of dicotyledon and animal AChE. The plant AChE hydrolyzed acetylcholine, propionylcholine, acetylthiocholine, propionylthiocholine, but not S-butyrylthiocholine and the AChE-specific inhibitor neostigmine bromide competitively inhibited its activity, implying that maize AChE functions in a similar manner as an eel AChE. However, both plant AChE showed a lower affinity to substrates and inhibitor than an eel AChE, and not exhibited the inhibition by excess substrate condition. Thus structural difference around active site between plant and animal AChE might be involved in differential inhibitory effect.
