title: A new perspective on thermal inactivation kinetics of human serum butyrylcholinesterase.
abstract: Butyrylcholinesterase purified from human serum as 6600-fold was heated at 37 degrees, 40 degrees, 45 degrees, and 50 degrees C for 24 hr. It was observed that the enzyme heated at 45 degrees C for 24 hr converted to a stabilized form and followed Michaelis-Menten kinetics, whereas the enzyme samples, heated at the other temperatures for 24 hr, shown negative cooperativity with respect to its substrate, butyrylthiocholine. Even the sample heated at 45 degrees C for 12 hr shown negative cooperativity. On the contrary to the heated enzyme at 40 degrees C for 24 hr, the heated enzyme at 45 degrees C for 24 hr could not be reactivated when it was kept at 4 degrees C for 24 hr. In the kinetic studies, it was found that substrate analogs choline and benzoylcholine inhibited both the native enzyme and the enzyme heated at 45 degrees C for 24 hr competitively, whereas succinylcholine was the partial competitive inhibitor of native enzyme but the pure competitive inhibitor of the heated enzyme.
authors.affiliation: Faculty of Medicine, Hacettepe University, Department of Biochemistry, Ankara, Turkey.
authors.forename: D
authors.initials: D
authors.lastname: Cengiz
authors.forename: A N
authors.initials: AN
authors.lastname: Cokuğraş
authors.forename: E F
authors.initials: EF
authors.lastname: Tezcan
mesh_terms: D001667:Binding, Competitive; D002091:Butyrylcholinesterase / Q000097:blood* / Q000737:chemistry* / Q000378:metabolism; D002794:Choline / Q000031:analogs & derivatives / Q000378:metabolism; D002800:Cholinesterase Inhibitors / Q000737:chemistry; D004789:Enzyme Activation; D006358:Hot Temperature; D006801:Humans; D007700:Kinetics; D011489:Protein Denaturation; D013816:Thermodynamics
chemical_list: D002800:Cholinesterase Inhibitors; D002091:Butyrylcholinesterase; D002794:Choline