A QUATERNARY CARBON ANALOGUE OF ACETYLTHIOCHOLINE AS SUBSTRATE FOR CHOLINESTERASES

1. The quaternary carbon analogue of acetylthiocholine (AThCh), 3.3-dimethylbuthylthioacetate (DMBTA), has been synthesized and subjected to a preliminary investigation as substrate for cholinesterase (ChE). 2. Acetylcholinesterase was found to hydrolyze DMBTA at 25% of the rate of AThCh when both substrates were used in a concentration of 6×10-4M. For butyrylcholinesterase the corresponding percentage was 30. Michaelis constants and Vmax for DMBTA and each of the two main types of ChE were determined. 3. DMBTA was tested as a substrate for histochemical ChE staining in rat diaphragms. The histochemical procedure employed corresponded to the AThCh method (Koelle and Fkiedenwald, 1949) with some minor modifications. The staining gave a distinct, but not very dense picture of the endplates with a clear background. 4. The lack of electrical charge in DMBTA, the bearing of this on lipoid and water solubility and the possible power of this substrate to penetrate biological membranes are discussed. The importance of these factors in histochemistry of less accessible ChE, e.g. in subcellular structures, is pointed out. © 1968 Springer-Verlag.