Purpose of liver extract in the Ames test?

In the Ames test, a widely used bacterial mutagenicity assay, liver extract is added as a source of cofactors and enzymes required for the activation of promutagens to their mutagenic forms. The liver extract is typically derived from rat or mouse liver and contains various enzymes, including cytochrome P450 monooxygenases, flavin-containing monooxygenases, and glutathione S-transferases, which are involved in the metabolism and activation of promutagens.

Protagens are chemicals or compounds that have the potential to cause mutations but require metabolic activation to exert their mutagenic effects. Liver extract provides the necessary metabolic enzymes that can convert promutagens into their active mutagenic intermediates. These activated promutagens can then interact with and damage the DNA of the tester strains used in the Ames test, leading to mutations and the detection of mutagenic potential.

The addition of liver extract to the Ames test allows for the assessment of the mutagenicity of compounds that require metabolic activation. It helps to identify potential mutagens that may not be directly mutagenic but can undergo metabolic conversion to become mutagenic. This feature makes the Ames test a more comprehensive and sensitive method for detecting a wide range of mutagenic compounds.