Human cytochrome P450 11B2 produces aldosterone by a processive mechanism due to the lactol form of the intermediate 18-hydroxycorticosterone [Metabolism]

We present here a comprehensive investigation of processivity in P450 11B2–catalyzed reactions using steady-state, pre-steady–state, pulse-chase, equilibrium-binding titrations, and stopped-flow binding studies. We utilized the data obtained to develop a kinetic model for P450 11B2 and tested this model by enzyme kinetics simulations. We found that although aldosterone is produced processively, the enzyme preferentially utilizes a distributive mechanism that ends with the production of 18-OH corticosterone. This seemingly contradictory observation could be resolved by considering the ability of the intermediate product 18-OH corticosterone to exist as a lactol form, with the equilibrium favoring the ring-closed lactol configuration. In summary, our refined model for P450 11B2 catalysis indicates isomerization of the intermediate to a lactol can explain why P450 11B2 must produce aldosterone through a processive mechanism despite favoring a distributive mechanism.
Source: Journal of Biological Chemistry - Category: Chemistry Authors: Tags: Enzymology Source Type: research