{{ ::phenyldiazene.png?600 |}} Active site topology of a P450 enzyme tested by formation of phenyl-porphyrin adducts. In this example, an adduct with pyrrole ring A is formed. The ratio of the four possible adducts indicates the degree of encumbrance over the heme in the native P450 protein. {{ ::fig7crt.png?600|}} From Andersen et al. 1997.