Stability of butyrylcholinesterase: thermal inactivation in water and deuterium oxide.
Irreversible thermal inactivation of the tetrameric form of human plasma butyrylcholinesterase (cholinesterase; EC 3.1.1.8) was studied in water and in deuterium oxide at pH 7 in the temperature range 53-65 degrees C. The enzyme inactivation follows a complex kinetics that may be described by the sum of two apparent first-order processes. The Eyring plot for enzyme inactivation exhibits a wavelike discontinuity over a span of 2 C degrees around 58 degrees C. This transition was interpreted in terms of equilibrium between two temperature-dependent conformational states. Though 2H2O does not alter the overall multistep inactivation process, a slight solvent isotope effect was observed: a stabilizing effect and a shift in the transition temperature. A comparison between several enzyme preparations revealed differences in thermodynamic activation parameters of inactivation suggesting microheterogeneity in enzyme structures. Kinetics of inactivation of usual (E1uE1u) and atypical (E1aEa1a++) enzymes were compared. The atypical enzyme was found to be more stable than the usual phenotype.
Masson
P
P
Centre d'Etudes et de Recherches Biophysiologiques, Division de Biochimie, Toulon-Naval, France.
Laurentie
M
M
D002091:Butyrylcholinesterase; D002800:Cholinesterase Inhibitors; D002802:Cholinesterases; D003903:Deuterium; D006358:Hot Temperature; D006801:Humans; D007700:Kinetics; D046911:Macromolecular Substances; D011489:Protein Denaturation; D013816:Thermodynamics; D014867:Water
D002800:Cholinesterase Inhibitors; D046911:Macromolecular Substances; D014867:Water; D003903:Deuterium; D002091:Butyrylcholinesterase; D002802:Cholinesterases