Couplisg of Acetyl Donor Systems with Cholixe Acetylase*

Previous studies of the choline acetylation system of brain and of the head ganglion of the squid have utilized acetate, ATP,’ and CoA to generate “active acetate” (1, 2). Following the isolation of acetyl CoA by Lynen et al. (3), its identity with “active acetate” has been established by the demonstration that the acetylated coenzyme is the acetyl donor in the biological acetylation of sulfanilamide (3), choline,* and orthophosphate (4), and in the synthesis of citrate (5) and acetoacetate (6). The synthesis of acetylcholine from acetyl CoA and choline has been confirmed with a partially purified choline acetylase from the head ganglion of the squid. Experiments on the coupling of choline acetylase with various acetyl donor systems, in the presence of catalytic amounts of CoA, are also report,ed. The acetyl donors used were acetyl phosphate, pyruvate, and citrate in the presence of phosphotransacet.ylase (4), the pyruvate oxidation system (7, S), and the condensing enzyme (5), respectively. Acetyl CoA As Acetyl Donor-An experiment demonstrating the enzymatic synthesis of acetylcholine from acetyl CoA and choline is given iu Table I. The formation of acetylcholine is accompanied by the appearance of a st.oichiometric amount of sulfhydryl groups. This indicates that the choline acetylase preparation employed catalyzes the following reaction. 0 Ii (1) Co&S-&-CHa + (CH,),NyCH,-CH,OH =