The inactivation process of native (N) human butyrylcholinesterase (BuChE) by hydrostatic pressure and/or heat was found to follow a complex first-order kinetics [1, 2]. This multistep process led to irreversible formation of an active intermediate (I) state and subsequently an inactivated (denatured) state. This process was described by expanding the Lumry-Eyring denaturation model. The intermediate state (I) was found to have a catalytic efficiency two-fold higher than that of the native state. This increase in catalytic activity can be explained by dehydration of the active site gorge, enhancing the nucleophilicity of the catalytic Ser198, and/or by a conformational change in the active site gorge, making the catalytic steps easier. The inactivation process of BuChE induced by the combined action of pressure and heat was found to continue after interruption of pressure/temperature treatment. This secondary inactivation process was termed "remnant inactivation". It was hypothesised that the N and I states were in equilibrium with populated metastable N' and I' states. The N' and I' states can either return to the active forms N and I or develop to inactive forms N'in and I'in. Both active N' and I' intermediate states displayed different rates of remnant inactivation depending on the pressure and temperature pretreatments and on the storage temperature. A first-order deactivation model describing the kinetics of the remnant inactivation of BuChE was proposed.

[1] Masson, P., Laurentie, M., Biochim. Biophys. Acta 957, 111-121, 1988.

[2] Weingand-Ziadé, A., Renault, R., Masson, P., Biochim. Biophys. Acta 1340, 245-252, 1997.