Effects of Ni2+, Co2+, and Mn2+ on Desensitized Butyrylcholinesterase Prepared from Human Serum

Human serum butyrylcholinesterase (BChE) has been converted into a stable but less active desensitized form when heated at 45°C for 24 h. The desensitized BChE follows Michaelis-Menten kinetics, whereas native enzyme exhibits slightly negative cooperativity with respect to butyrylthiocholine binding. In this study, we investigated the effects of Ni^sup 2+^, Co^sup 2+^, and Mn^sup 2+^ on the desensitized BChE. It is found that all three ions were noncompetitive inhibitors of the desensitized BChE, and K ^sub i^ values have been determined as 7.816±1.060 mM, 48.722±4.635 mM, and 84.795±5.249 mM for Ni^sup 2+^, Co^sup 2+^, and Mn^sup 2+^, respectively. In our previous study, these ions were linear mixed-type inhibitors of the native BChE. This finding confirms that desensitized BChE changes to a different conformation than native BChE. From the comparison of K ^sub i^ values of the trace elements, it can be said that Ni^sup 2+^ is a more effective inhibitor of the desensitized BChE than Co^sup 2+^ and Mn^sup 2+^.[PUBLICATION ABSTRACT]