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Overview of the use of the SOS response for genotoxicity testing. The SOS chromotest is a biological assay to assess the genotoxic potential of chemical compounds. The test is a colorimetric assay which measures the expression of genes induced by genotoxic agents in Escherichia coli, by means of a fusion with the structural gene for β-galactosidase.
β-Galactosidase is an exoglycosidase which hydrolyzes the β-glycosidic bond formed between a galactose and its organic moiety. It may also cleave fucosides and arabinosides but at a much lower rate. It is an essential enzyme in the human body. Deficiencies in the protein can result in galactosialidosis or Morquio B syndrome.
A simple colorimetric test is possible by adding a lactose analog which is degraded by β-galactosidase, producing a colored compound which can be measured quantitatively through spectrophotometry. The degree of color development is an indirect measure of the β-galactosidase produced, which itself is directly related to the amount of DNA damage.
Senescence-associated beta-galactosidase, along with p16 Ink4A, is regarded to be a biomarker of cellular senescence. [ 1 ] [ 2 ] Its existence was proposed in 1995 by Dimri et al. [ 3 ] following the observation that when beta-galactosidase assays were carried out at pH 6.0, only cells in senescence state develop staining.
One common method includes enzyme assays which measure the activity of neuraminidase-1 and beta-galactosidase. [4] Decreased levels in enzymatic activity indicate a deficiency in cathepsin A. A complete urinalysis can be performed to detect the presence of oligosaccharides , [ 4 ] which would pass through the urine as excess amounts accumulate ...
The presence of an active β-galactosidase can be detected by X-gal, a colourless analog of lactose that may be cleaved by β-galactosidase to form 5-bromo-4-chloro-indoxyl, which then spontaneously dimerizes and oxidizes to form a bright blue insoluble pigment 5,5'-dibromo-4,4'-dichloro-indigo. This results in a characteristic blue colour in ...
ortho-Nitrophenyl-β-galactoside (ONPG) is a colorimetric and spectrophotometric substrate for detection of β-galactosidase activity. [1] This compound is normally colorless. However, if β-galactosidase is present, it hydrolyzes the ONPG molecule into galactose and ortho-nitrophen
A lactose analog is added to the bacteria, which is then degraded by beta-galactosidase, thereby producing a colored compound which can be measured quantitatively through spectrophotometry. The degree of color development is an indirect measure of the beta-galactosidase produced, which itself is directly related to the amount of DNA damage.