CHARACTERIZATION OF THE INHIBITION OF P4501A2 BY FURAFYLLINE

1. Furafylline inhibition of 1A2-related activity in human liver micro somal systems was characterized. This inhibition was time and NADPH de pendent. The kinetic constants were measured in human liver microsomes ; a K-i of inactivation of 3 mu M with a maximum rate constant of 0.27 min(-1) were determined. 2. This inactivation process was retarded by the presence of a 1A2 substrate and after complete inhibition was ach ieved, 1A2 activity could be restored by the addition of fresh microso mes to the incubation mixture. These results are consistent with furaf ylline being a suicide substrate for 1A2. 3. Preincubating microsomes for 10 min with 10 mu M furafylline in the presence of NADPH, prior to the initiation of the reaction by the addition of substrate, caused m arked inhibition of 1A2 activity. This protocol was tested for specifi city against 10 human P450 activities. The activities associated with 1A1, 2A6, 2B6, 2C9(/8), 2C19, 2D6, 2E1, 3A4(/5) and A were not signifi cantly inhibited. 4. Using these conditions furafylline call be diagno stic of 1A2 involvement in a P450-dependent oxidative reaction.