Typically, such chromogenic substrates are composed of 3 to 5 natural or artificial amino acids. They may be N-terminally protected to reduce undesired degradation by aminopeptidases.
On their C-termini they are modified so that upon cleavage of the amide bond a chromogenic group is released. Most commonly used groups are the p-nitroaniline (pNA) which absorbs light of the wavelength of 405 nm.
Lyophilized substrate which should be stored in the dark at room temperature, after reconstitution, store 1 week at room temperature in the dark, 2 months at 2-8 ° C and more than 6 months at -20 ° C. Aliquot and freeze and avoid freeze and thaw cycles.