A cell surface-localized acetylcholinesterase in the cellular slime mold Polysphondylium violaceum

Abstract The cellular slime mold Polysphondylium violaceum was found to synthesize a plasma membrane-bound acetylcholinesterase that is located on the surface of growing amoebae. Enzyme activity declines as cells approach stationary phase and is undetectable 2h after asexual differentiation has begun. The enzyme has a K _m value of approx. 46 μM and a V _max of 3 pmol · min⁻¹ (10⁷ cells)⁻¹. It shows substrate inhibition by acetylcholine and is inhibited by the true cholinesterase inhibitor BW248c51 but is weakly inhibited by N, N '-diisopropylphosphorodiamidic anhydride ( iso -OMPA), a pseudocholinesterase inhibitor. These results expand upon an earlier study which suggested that P. violaceum amoebae are able to respond to acetylcholine and other pharmacologically related compounds. Both studies suggest that an acetylcholine-based sensory system might operate during growth and early stages of P. violaceum differentiation.