Purification and Properties of Choline Acetyltransferase From the Nervous System of Different Invertebrates

Abstract —Choline acetyltransferase has been purified from three invertebrate species, namely snail ( Helix aspersa ), cockroach ( Periplaneta americana ) and horse shoe crab ( Limulus polyphemus. ) All three enzymes followed a Theorell‐Chance enzyme mechanism with a sequential addition of the substrates. All three enzymes were activated by sodium and potassium chloride and inhibited by high concentrations of magnesium or calcium chloride. The apparent K m for choline and acetyl‐CoA was for snail: K mch = 370 μ m , K mAcetyl‐CoA = 51μ m ; cockroach:K mCh = 550 μ m , K mAcely‐CoA = 16 μ m horse shoe crab: K mCn = 2700 μ m K mAcctyl‐coA = 68 μ m CoA inhibited the enzymes competitively with respect to acetyl‐CoA and non‐competitively with respect to choline. Acetylcholine inhibited the enzymes competitively with respect to choline and non‐competitively with respect to acetyl‐CoA. All the enzymes were inhibited strongly by 5,5′‐dithiobis (2‐nitrobenzoate), iodoacetate, acryloylcholine, chloracetylcholine and 3‐bromacetonyltrimethyl‐ammonium. The enzymes were only weakly inhibited by the styrylpyridine derivatives. The isoelectric points were 5.3 and 5.0 for the horse shoe crab and cockroach enzymes respectively. All three enzymes showed low affinity for a cation‐exchanger (CM‐Sephadex).