Cytochrome enzymes (CYP) have a vital role in the metabolism of all nutrition and have been a subject of study for many decades. Currently it is important to elucidate their reactivity using modern techniques to be able to understand its function in the drug metabolism completely and thus to be able to develop new drugs which are able to act faster with less side effects. This dissertation provides combinatorial technique to investigate the catalytic role of CYP enzymes and it takes CYP1A2 as example. The results shown here explain clearly the role of the amino acids surrounding the active site in the activity of the enzyme. Even though, all the CYP consist of the same active site (Heme moiety) however they show different catalytic functions depend on the surrounding amino acids. Such characteristics cannot be followed using normal methods and it requires novel techniques such as the explained in this book