The Ames Test

The Ames test is an assay that determines the mutagenicity of a chemical compound. The test was designed by the bacteria geneticist, Prof. B. N. Ames, in the year 1975. The bacterium, Salmonella typhimurium is also used in the test. The test is based on the premise that any compound that is able to cause a mutation of the DNA of Salmonella is definitely mutagenic. The Salmonella is a prokaryote. The mutagenicity of a compound on Salmonella invariably means that it can be mutagenic on human DNA and even turn out to be carcinogenic. The Ames test is highly reliable as most compounds that give a positive Ames test turn out to be mutagenic. However, some compounds which give a negative Ames test still turn out to be carcinogenic. Moreover, the fact that a compound is not mutagenic on Salmonella DNA does not mean it cannot be carcinogenic on human DNA.This might be due to the following reasons.

Some compounds are not by themselves carcinogenic but their metabolites are highly carcinogenic. For these compounds, they will give a negative Ames test if they were to undergo the test. These compounds will only give become carcinogenic after being metabolised in the human body. Most of these metabolisms take place in the Liver by a group of enzymes known as the Cytochrome P450 enzymes. These enzymes are present in the Smooth Endoplasmic Reticulum of the Liver. if it is to be determined if the metabolite of a compound is carcinogenic, then it has to a Rat liver homogenate is to be added to the slide containing the slide containing the preparation on which Ames test is to be carried out. The liver Homogenate contains the CyP450 enzymes and would definitely metabolise the compound. This would eventually give either a true positive or negative Ames test.

Also, the Ames test could be carried out on yeast or human cells instead of Salmonella because this will give a better result as to the mutagenicity of a compound on human DNA. Also, it should be noted that the fact that a compound is mutagenic in vitro does not necessarily mean that it will be mutagenic in vivo.

REFERENCES.

http://everything2.com/index.pl?node_id=1344695&displaytype=printable&lastnode_id=0

http://science.jrank.org/pages/281/Ames-Test.html

http://www.corante.com/pipeline/archives/2002/07/30/the_ames_test_and_the_real_world.php