Human aromatase is responsible for estrogen biosynthesis and is implicated, in particular, in reproduction and estro-gen-dependent tumor proliferation. Themolecular structure model is largelyderived fromtheX-ray structure of bacterial cytochromes sharing only 15±20% identities with hP-450arom. In the present study, site directed mutagenesis experiments were performed to examine the role of K119, C124, I125, K130, E302, F320, D309, H475, D476, S470, I471 and I474 of aromatase in catalysis and for substrate binding
