Cytochrome P450 52 (CYP52), also called P450ALK, monooxygenases catalyze the first hydroxylation step in the assimilation of alkanes and fatty acids by filamentous fungi. The number of CYP52 proteins depend on the fungal species: for example, Candida tropicalis has seven, Candida maltose has eight, and Yarrowia lipolytica has twelve. The CYP52 family belongs to the large cytochrome P450 (P450, CYP) superfamily of heme-containing proteins that catalyze a variety of oxidative reactions of a large number of structurally different endogenous and exogenous compounds in organisms from all major domains of life. CYPs bind their diverse ligands in a buried, hydrophobic active site, which is accessed through a substrate access channel formed by two flexible helices and their connecting loop.