Endo-xenobiotic crosstalk and the regulation of cytochromes P450

Evolution has provided organisms with an elaborate defense system against foreign compounds and against the accumulation of potentially toxic endogenous molecules, e.g. bile acids. Cytochromes P450 represent an important group of enzymes in this system. This article describes experiments started in the 1970's in Dallas on the coordination of heme and cytochrome P450 synthesis and how these studies evolved over the years into a concept of molecular links between xenobiotic metabolism and endogenous pathways of sterol, lipid, bile acid and energy homeostasis.