4-Nitrophenyl α-D-galactopyranoside (PNP-alpha-D-Gal) is an artificial substrate of 4-nitrophenyl (pNP) glycopyranoside for detecting α-galactosidase activity. The amount of released pNP is significantly increased when 4-Nitrophenyl α-D-galactopyranoside is used as substrates.
Using 4-nitorophenol (pNP)-glycopyranosides as pseudosubstrates, the amount of liberated pNP from the 4-Nitrophenyl α-D-galactopyranoside is significantly higher than that from the other pNP-glycopyranosides at pH 4.0 whereas no activity was detected at pH 7.0[1].
The digestion assays using 4-nitrophenyl (pNP) glycopyranosides as artificial substrates shows that yieldin liberated galactose residues from 4-Nitrophenyl α-D-galactopyranoside mainly at pH 4.0, i.e. the pH level where yield threshold is decreased at most[1].
References:
[1]. Okamoto-Nakazato A. Implications of the galactosidase activity of yieldin in the regulatory mechanism of yield threshold that is fundamental to cell wall extension. Physiol Plant. 2018 Jun;163(2):259-266.