Aromatic hydroxylations in peroxidations by haemoglobin systems

1. The catalytic activity of haemoglobin on aromatic substrates was studied in three systems: NADH-methylene blue-haemoglobin, ascorbic acid-haemoglobin, and red blood cells. 2. Aniline and phenol but not acetanilide or p-toluidine are hydroxylated by haemoglobin. Dealkylations are not observed. Hydroxylations are postulated to be intermediate reactions in peroxidations catalysed by haemoglobin. 3. The lifetime of the products depends on the presence of electron donors, such as NADH or ascorbic acid, in the medium. 4. In the red blood cells where endogeneous electron donors are recycled, levels of the products are higher and their lifetime is longer. This could have implications on drug metabolism by haemoglobin, as haemoglobin is present in large quantities in the organism.