p-Nitrophenol (PNP substrates)

4-Nitrophenol or PNP (product code 38XXX) and 2-nitrophenol or ONP (product code 24XXX) substrates are colourless compounds which offer a diffuse yellow endpoints following enzymatic cleavage, making them best suited for use in liquid media applications. The coloration of nitrophenols in aqueous solution is pH-dependent as deprotonation of the hydroxyl group is required for generation of a chromophore. The strongest colouration is achieved at pH values above 9.0, this is typically achieved by the addition of a base after a defined reaction time at neutral pH. The colouration of the phenolate ion can be measured using a spectrophotometer at 405 nm.

The substrates are widely used in diagnostic microbiology as they have the advantage of being stable and offering a district colour change on hydrolysis.

Glycosynth offers a wide range of nitrophenyl based substrates including 4-Nitrophenyl beta-D-glucopyranoside (product code 38059) for the detection of beta-D-glucosidase activity and p-nitrophenyl glycerol (product code 38181) which is used as an antimicrobial agent due to it inhibiting bacterial growth. o-Nitrophenyl beta-D-galactopyranoside ONPG (product code 24045) is used to detect beta-galactosidase activity, often being employed as an indicator of total coliforms in dual substrate systems.