The S9 fraction is the product of an organ tissue
homogenate
Homogeneity and heterogeneity are concepts often used in the sciences and statistics relating to the uniformity of a substance or organism. A material or image that is homogeneous is uniform in composition or character (i.e. color, shape, s ...
used in
biological assay
An assay is an investigative (analytic) procedure in laboratory medicine, mining, pharmacology, environmental biology and molecular biology for qualitatively assessing or quantitatively measuring the presence, amount, or functional activity of a ...
s. The S9 fraction is most frequently used in assays that measure the
metabolism
Metabolism (, from el, μεταβολή ''metabolē'', "change") is the set of life-sustaining chemical reactions in organisms. The three main functions of metabolism are: the conversion of the energy in food to energy available to run cell ...
of drugs and other
xenobiotic
A xenobiotic is a chemical substance found within an organism that is not naturally produced or expected to be present within the organism. It can also cover substances that are present in much higher concentrations than are usual. Natural compo ...
s. It is defined by the
U.S. National Library of Medicine
The United States National Library of Medicine (NLM), operated by the United States federal government, is the world's largest medical library.
Located in Bethesda, Maryland, the NLM is an institute within the National Institutes of Health. Its ...
's "
IUPAC
The International Union of Pure and Applied Chemistry (IUPAC ) is an international federation of National Adhering Organizations working for the advancement of the chemical sciences, especially by developing nomenclature and terminology. It is ...
Glossary of Terms Used in Toxicology" as the "
Supernatant
In an aqueous solution, precipitation is the process of transforming a dissolved substance into an insoluble solid from a super-saturated solution. The solid formed is called the precipitate. In case of an inorganic chemical reaction leading ...
fraction obtained from an organ (usually liver) homogenate by
centrifuging at 9000 g for 20 minutes in a suitable medium; this fraction contains
cytosol
The cytosol, also known as cytoplasmic matrix or groundplasm, is one of the liquids found inside cells (intracellular fluid (ICF)). It is separated into compartments by membranes. For example, the mitochondrial matrix separates the mitochondri ...
and
microsomes
In cell biology, microsomes are heterogeneous vesicle-like artifacts (~20-200 nm diameter) re-formed from pieces of the endoplasmic reticulum (ER) when eukaryotic cells are broken-up in the laboratory; microsomes are not present in healthy, livin ...
." The microsomes component of the S9 fraction contain
cytochrome P450
Cytochromes P450 (CYPs) are a Protein superfamily, superfamily of enzymes containing heme as a cofactor (biochemistry), cofactor that functions as monooxygenases. In mammals, these proteins oxidize steroids, fatty acids, and xenobiotics, and are ...
isoforms (
phase I metabolism
Drug metabolism is the metabolic breakdown of drugs by living organisms, usually through specialized enzymatic systems. More generally, xenobiotic metabolism (from the Greek xenos "stranger" and biotic "related to living beings") is the set o ...
) and other enzyme activities. The cytosolic portion contains the major part of the activities of
transferase
A transferase is any one of a class of enzymes that catalyse the transfer of specific functional groups (e.g. a methyl or glycosyl group) from one molecule (called the donor) to another (called the acceptor). They are involved in hundreds of di ...
s (
phase II metabolism
Drug metabolism is the metabolic breakdown of drugs by living organisms, usually through specialized enzymatic systems. More generally, xenobiotic metabolism (from the Greek xenos "stranger" and biotic "related to living beings") is the set of ...
). The S9 fraction is easier to prepare than purified microsomes.
Applications
The S9 fraction has been used in conjunction with the
Ames test to assess the
mutagenic
In genetics, a mutagen is a physical or chemical agent that permanently changes genetic material, usually DNA, in an organism and thus increases the frequency of mutations above the natural background level. As many mutations can cause cancer in ...
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.
References
Further reading
*
External links
"U.S. National Library of Medicine"(NLM)
* NLM'
Cell biology
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