Differential reactivity of active sites in XXXX plasma cholinesterase toward @entity12259 .

@entity1 @entity1169 @entity12259 @entity26408 @entity8696 @entity1387
@entity1 plasma cholinesterase was found to be inhibited by @entity12259 in a biphasic manner. The faster phase of the inhibition led to loss of approximately 50% of the activity (measured at pH 7.0, 30 degrees C, using 2.5 mM @entity1387 ) and was irreversible. Inhibition in the slower phase was reversible by 0.25 M @entity8696 . The protective effect of 1 mM @entity1169 indicated that the target residue in both phases was localized at the active site. Lineweaver-Burk plots for @entity1387 were obtained at different times during the course of inactivation. It was found that for both native and partially inactivated enzymes the plots could be analyzed in terms of two activities showing hyperbolic saturation with the substrate, with Km values of 0.055 +/- 0.015 and 2.0 +/- 0.2 mM. The @entity26408 affected the maximal velocities of the component activities, leaving the Km's unchanged. The low-Km component was lost in the first phase of the inactivation. The loss of the high-Km component paralleled the second phase. It was concluded that the active sites in the tetrameric enzyme form two classes, differing in their affinity for @entity1387 and their susceptibility to inhibition by the active site-directed @entity26408 .
