Description_x000D_ Biochem/physiol Actions_x000D_ Liver microsomes are subcellular particles derived from the endoplasmic reticulum of hepatic cells. These microsomes are a rich source of drug metabolizing enzymes, including cytochrome P-450. Microsome pools from various sources are useful in the study of xenobiotic metabolism and drug interactions._x000D_ Unit Definition_x000D_ One unit will reduce 1 nanomole of cytochrome C per minute at pH 7.4 at 37 deg C._x000D_ 7-ethoxyresorufin O-deethylase activity: One unit will hydroxylate 1.0 picomole paclitaxel per minute at pH 7.4 at 37 deg C.