Relationship between paracetamol binding to and its oxidation by two cytochromes P-450 isozymes—a proton nuclear magnetic resonance and spectrophotometric study

Abstract

1. From the hepatic cytochrome P-450 isozymes b and c isolated from rats treated with phenobarbital and 3-methylcholanthrene respectively, only cytochrome P-45012 was found to be active in the oxidation of paracetamol, in the presence of glutathione ultimately leading to the formation of the 3-glutathionyl conjugate.

2. Paracetamol interacted with both cytochrome P-450b and c, as shown by difference spectrophotometry. Cytochrome P-45Ob was found to have a higher affinity for paracetamol than cytochrome P-45Oc and demonstrated a type I spectral change, whereas in the case of cytochrome P-450c a reverse type I spectral change was observed.

3. Proton n.m.r. longitudinal relaxation rate measurements revealed that in the case of cytochrome P-45Oc, paracetamol was orientated with its phenolic hydroxyl group in closest proximity to the central haem iron ion. In the case of cytochrome P-45Ob, the acetylamino group of paracetamol most closely approached the haem iron ion.