Kinetics of heat inactivation of @entity71119 hydrolases from hen and XXXX brain.

@entity6000 @entity3733 @entity71119 @entity35 @entity1098 @entity2359
Heat inactivation was studied at 45, 50, 55, and 60 degrees for all of the @entity71119 hydrolases (PVase), including @entity2359 esterase (NTE) and inhibitor-resistant esterase (IRE), in homogenates of hen or @entity35 brain or in preparations of hen brain microsomal membranes. Hen and @entity35 brain homogenates were prepared in buffer (50 mM Tris/0.20 mM @entity1098 , pH 8.00, at 25 degrees). Hen brain microsomes were suspended either in buffer or in aqueous @entity3733 ( @entity3733 , 40%, w/v), or solubilized either in aqueous @entity6000 (0.10%, w/v) or in 40% (w/v) @entity3733 . Enzyme activities were measured at 37 degrees using @entity71119 as substrate. Each enzyme activity in all of the preparations exhibited biphasic heat inactivation kinetics. Apparent rate constants were calculated for the fast (kf) and slow (ks) reactions, along with the relative amounts of activity in each component (Af, As) expressed as percentages of the total activity. For a given preparation and temperature, respective values of kf or ks were similar for PVase, NTE, and IRE, with a mean kf/ks ratio of 52 across all preparations. Af and As were a function of temperature. Mean values of the apparent activation energies (Ea) for all activities and preparations were 44 and 25 kcal/mol for the fast and slow inactivation reactions respectively. These results indicate that all @entity71119 hydrolases in hen and @entity35 brain undergo a common heat-induced structural change leading to loss of enzymic activity.
