Due to bacteria being unable to metabolize molecules, the mutagenic potential of samples is assessed directly and in the presence of metabolic activation system: Microsomal fraction S9 of Phenobarbital/ß-Naphtoflavone induced hamster liver homogenate. Hamster liver S9 is used preferentially in the Enhanced Ames Test (OECD 471) for Nitrosamines, or in ADME (pharmacokinetic studies) for pharmaceutical preparations.

Phenobarbital/ß-Naphtoflavone induced hepatic S9 is a buffered solution containing the post mitochondrial S9 fraction of a pool of livers from Golden Syrian Hamster. Liver S9 fractions (the 9000g supernatant of a liver homogenate) contain both microsomal and cytosolic fractions. S9 fraction includes many cytosolic enzymes: N-acetyl transferases, methyltransferases, sulfotransferases, glutathione transferases, aldehyde oxidase, xanthine oxidase. Both Phase I (Cytochrome P450-Monooxigenases) and Phase II metabolites act simultaneously on test samples. Due to the fact that the enzymes in the S9 fractions are diluted significantly, cofactors such as e.g. β-Nicotinamide adenine dinucleotide phosphate-regenerating system (NADPH, Phase I oxidation) are required for activity. Cofactors are added to the S9 preparation before the experiment (S9 Cofactor Kit, art.no. PCO-0800, PCO-1800).