HYDROPHILIC AND AMPHIPHILIC FORMS OF DROSOPHILA CHOLINE-ACETYLTRANSFERASE ARE ENCODED BY A SINGLE MESSENGER-RNA

We have previously shown that the enzyme choline-O-acetyltransferase ( ChAT) exists in a hydrophilic and an amphiphilic form in Drosophila he ad. A complementary DNA clone of 4.2 kb containing the entire coding r egion of ChAT was isolated from a cDNA library of Drosophila heads. Th e cDNA was subcloned in an expression vector and injected into the nuc leus of Xenopus oocytes. Injected oocytes expressed high levels of ChA T activity. This activity was inhibited by bromoacetylcholine, a speci fic inhibitor of the enzyme. In the present study the non-ionic deterg ent Triton X-114 was used to analyse whether the expression of hydroph ilic and amphiphilic ChAT was or was not directed by a single cDNA. Th e two forms of ChAT were found to be synthesized in injected oocytes. Approximately 9% of the recombinant enzyme partitioned as amphiphilic activity. This value was similar to that found for native amphiphilic ChAT in Drosophila heads. Sedimentation in sucrose gradients of amphip hilic enzyme was found to be influenced by the type of detergent prese nt in the gradient whereas this was not the case for hydrophilic ChAT. Hydrophilic and amphiphilic enzyme activities differed in some of the ir biochemical properties. Amphiphilic ChAT was less sensitive to inhi bition by the product acetylcholine than was hydrophilic ChAT. Moreove r, amphiphilic ChAT was found to be more resistant than hydrophilic Ch AT to heat inactivation at 45 degrees C. These properties were observe d for the native as well as for recombinant ChAT. These results demons trate that the hydrophilic and amphiphilic forms of ChAT are derived f rom one mRNA.