title: On the mechanism of action of choline acetyltransferase.
abstract: The substrate specificity of choline acetyltransferase (EC 2.3.1.6) isolated from squid ganglia was investigated. The enzyme catalyzed the acetylation of choline and aminocholine but not of homocholine. In D(2)O solution there was considerable slowing of the transacetylation reaction. Photo-oxidation in the presence of methylene blue or rose bengal rapidly inactivated the enzyme, suggesting involvement of a histidine residue in the catalytic site. It seems likely that general-base catalysis by imidazole enhances the ability of enzyme-bound choline (or ammoniumcholine) to react with a thiolester group. Attempts to isolate an acetylthio-enzyme intermediate after incubation with [(14)C]acetylcoenzyme A were unsuccessful. A possible mechanism for the action of choline acetyltransferase is proposed.
mesh_terms: D000105:Acetyl Coenzyme A / Q000378:metabolism; D000123:Acetyltransferases / Q000037:antagonists & inhibitors / Q000378:metabolism*; D000818:Animals; D002250:Carbon Radioisotopes; D002794:Choline / Q000031:analogs & derivatives; D002850:Chromatography, Gel; D049832:Decapodiformes; D003903:Deuterium; D005724:Ganglia / Q000201:enzymology; D006863:Hydrogen-Ion Concentration; D007093:Imidazoles; D008751:Methylene Blue; D010777:Photochemistry; D012395:Rose Bengal; D013438:Sulfhydryl Compounds
chemical_list: D002250:Carbon Radioisotopes; D007093:Imidazoles; D013438:Sulfhydryl Compounds; C007954:homocholine; D012395:Rose Bengal; C006518:aminocholine; D000105:Acetyl Coenzyme A; D003903:Deuterium; D000123:Acetyltransferases; D002794:Choline; D008751:Methylene Blue