ortho-Nitrophenyl--galactoside

For R&D use onlynot for drug household or other uses.

ortho-Nitrophenyl--galactoside (ONPG) is a colorimetric and spectrophotometric substrate for detection of -galactosidase activity. This compound is normally colorless. However if -galactosidase is present it hydrolyzes the ONPG molecule into galactose and ortho-nitrophenol. The latter compound has a yellow color that can be used to check for enzyme activity by means of a colorimetric assay (at 420nm wavelength). -Galactosidase is required for lactose utilization so the intensity of the color produced can be used as a measure of the enzymatic rate.