The S9 fraction is the product of a organ tissue homogenate

Homogenization (biology)

Homogenization is a process that involves breaking apart cells — releasing organelles and cytoplasm.When the purpose is to extract organelles, it is frequently done in two steps; first using a blender to break the tissue up, and then with an ultrasonic or mechanical tissue disruptor. The...

 used in biological assay

Bioassay

Bioassay , or biological standardization is a type of scientific experiment. Bioassays are typically conducted to measure the effects of a substance on a living organism and are essential in the development of new drugs and in monitoring environmental pollutants...

s. The S9 fraction is most frequently used in assays that measure the metabolism

Metabolism

Metabolism is the set of chemical reactions that happen in the cells of living organisms to sustain life. These processes allow organisms to grow and reproduce, maintain their structures, and respond to their environments. Metabolism is usually divided into two categories...

 of drugs and other xenobiotic

Xenobiotic

A xenobiotic is a chemical which is found in an organism but which is not normally produced or expected to be present in it. It can also cover substances which are present in much higher concentrations than are usual...

s. It is defined by the U.S. National Library of Medicine's "IUPAC Glossary of Terms Used in Toxicology" as the "Supernatant fraction obtained from an organ (usually liver) homogenate by centrifuging

Centrifuge

A centrifuge is a piece of equipment, generally driven by an electric motor , that puts an object in rotation around a fixed axis, applying a force perpendicular to the axis...

 at 9000 g for 20 minutes in a suitable medium; this fraction contains cytosol

Cytosol

The cytosol or intracellular fluid is the liquid found inside cells, that is separated into compartments by membranes. For example, the mitochondrial matrix separates the mitochondrion into compartments....

 and microsomes." The microsomes component of the S9 fraction contain cytochrome P450 isoforms (phase I metabolism) and other enzyme activities. The cytosolic portion contains the major part of the activities of transferase

Transferase

In biochemistry, a transferase is an enzyme that catalyzes the transfer of a functional group from one molecule to another . For example, an enzyme that catalyzed this reaction would be a transferase:In this example, A would be the donor, and B would be the acceptor...

s (phase II metabolism). The S9 fraction is easier to prepare than purified microsomes.

Applications

The S9 fraction has been used in conjunction with the Ames test

Ames test

The Ames test is a biological assay to assess the mutagenic potential of chemical compounds. A positive test indicates that the chemical is mutagenic and therefore may act as a carcinogen, since cancer is often linked to mutation. However, a number of false-positives and false-negatives are known...

 to assess the mutagenic potential of chemical compounds. Chemical substances sometimes require metabolic activation in order to become mutagenic. Furthermore the metabolic enzymes of bacteria used in the Ames test differ substantially from those in mammals. Therefore to mimic the metabolism of test substance that would occur in mammals, the S9 fraction is often added to the Ames test.

The S9 fraction has also been used to assess the metabolic stability of candidate drugs.

External links

• "U.S. National Library of Medicine" (NLM)
• NLM's "IUPAC Glossary of Terms Used in Toxicology"