human liver S9 fraction A mixture of cell cytosol and microsomes isolated by disruption and centrifugation of human liver cells. It contains a wide range of drug-metabolizing enzymes and is commonly used for in vitro DMPK studies, including both phase I and phase II xenobiotic metabolism. John Judkins a processed material that has a supernatant role resulting from medium-speed centrifugation of a human liver homogenate processed material