Chromogenic Substrates
Chromogenic Substrates are colourless compounds that consist of a chromophore linked to an enzyme active group, typically a sugar, a phosphate or an ester group, that is recognized and acted upon by an enzyme to produce a visible distinctive coloured end point. This colour change visually provides a qualitative detection of a target enzyme or quantitative detection can be achieved using a chromogenic assay. Chromogenic substrates can provide a non-diffuse end-point that is tightly localised to bacterial colonies or a diffuse end-point more suited to liquid media. Indoxyl esters and glycosides are useful chromogenic substrates for detecting enzyme activities in histochemistry, biochemistry and bacteriology.
Chromogenic Substrate Categories
Chromogenic indoxyl substrates were used in the early 1950’s for use in histochemistry but by the 1970’s were widely developed for use to detect bacteria. Indoxyl substrates continue to be an invaluable tool in diagnostic microbiology, molecular biology. An advantage offered by indoxyl substrates is that, when used the presence of oxygen, they provide a non-diffuse coloured end-point, making them suitable for use in solid media. The liberated indoxyl compound dimerises in the presence of oxygen to give highly coloured compound that is tightly localised to bacterial colonies. Glycosynth’s offers a wide range of indoxyl substrates including 5-bromo-4-chloro-3-indolyl or X-substrates (product code 70XXX) that give a blue/green coloured end-point, 5-bromo-6-chloro-3-indolyl or mag substrates (product code 31XXX) that give a purple end-point and 6-chloro-3-indolyl or rose-substrates (product code 60XXX) that offer a pink colour after enzymatic hydrolysis.
Another series of chromogenic substrates that can give a non-soluble end-point are the metal chelating substrates. These include 8-hydroxyquinoline substrates (product code 35XXX), 3,4-cyclohexenoesculetin or CHE substrates (product code 75XXX), 6,7-dibromo-2,3-dihydroxynaphthalene or brown-substrates (product code 56XXX), alizarin substrates (product code 89XXX)and the more soluble alizarin sodium salt substrates (product code 51XXX). These substrates do not require the aerobic conditions that might be restrict the use of an indoxyl substrate and still give a non-diffuse end-point when used in the presence of a metal chelator, such as ferric ammonium citrate (FAC). Glycosynth also offer a number of chelating substrates with diffuse-end points making them more suited for use in liquid media; catechol substrates (product code 14XXX) give a brown coloured end-point and 2,3-dihydroxynaphthyl or DHN substrates (product code 80XXX) give a diffuse purple colour after hydrolysis.
Halonitrophenol substrates, p-nitrophenyl or PNP (product code 38XXX) and o-nitrophenyl or ONP (product code 24XXX) do not require aerobic conditions or the use of a metal chelator to produce a yellow diffuse end-points.
More information about Glycosynth’s full range chromogenic substrates can be found by clicking the relevant link below.
