title: The kinetic properties of human placental choline acetyltransferase.
abstract: 1. Michaelis constants for human placental choline acetyltransferase were shown to be dependent on the concentration of the second substrate present. The primary plots indicate a sequential rather than a Ping Pong mechanism and are of the same type with 300mm- and 500mm-sodium chloride. 2. Similar results have been obtained with rabbit brain choline acetyltransferase. 3. Product inhibition of the forward reaction has been studied. CoA inhibits competitively with respect to acetyl-CoA and non-competitively with respect to choline. Acetylcholine inhibits competitively with respect to choline and non-competitively with respect to acetyl-CoA. No inhibition is given by acetylcholine when the enzyme is saturated with choline. 4. It is concluded that human placental choline acetyltransferase has an ordered mechanism of the Theorell-Chance type.
mesh_terms: D000109:Acetylcholine / Q000096:biosynthesis / Q000494:pharmacology; D000217:Acyltransferases / Q000037:antagonists & inhibitors; D000818:Animals; D001921:Brain / Q000201:enzymology; D002794:Choline; D003065:Coenzyme A; D005260:Female; D006801:Humans; D007700:Kinetics; D008956:Models, Chemical; D010920:Placenta / Q000201:enzymology*; D011817:Rabbits
chemical_list: D000217:Acyltransferases; D002794:Choline; D000109:Acetylcholine; D003065:Coenzyme A