Shaihutdinova_2024_Molecules_29_2356

The beta-adrenergic drug Mirabegron, a drug initially used for the treatment of an overactive bladder, has new potential indications and is hydrolyzed by butyrylcholinesterase (BChE). This compound is one of the only arylacylamide substrates to be catabolized by BChE. A steady-state kinetic analysis at 25 degreesC and pH 7.0 showed that the enzyme behavior is Michaelian with this substrate and displays a long pre-steady-state phase characterized by a burst. The induction time, tau, increased with substrate concentration (tau = 18 min at maximum velocity). The kinetic behavior was interpreted in terms of hysteretic behavior, resulting from a slow equilibrium between two enzyme active forms, E and E'. The pre-steady-state phase with the highest activity corresponds to action of the E form, and the steady state corresponds to action of the E' form. The catalytic parameters were determined as k(cat) = 7.3 min(-1) and K(m) = 23.5 microM for the initial (burst) form E, and k(cat) = 1.6 min(-1) and K(m) = 3.9 microM for the final form E'. Thus, the higher affinity of E' for Mirabegron triggers the slow enzyme state equilibrium toward a slow steady state. Despite the complexity of the reaction mechanism of Mirabegron with BChE, slow BChE-catalyzed degradation of Mirabegron in blood should have no impact on the pharmacological activities of this drug.