The 4-carboxyaldehyde form of vitamin B6 which is converted to pyridoxal phosphate which is a coenzyme for synthesis of amino acids neurotransmitters (serotonin norepinephrine) sphingolipids aminolevulinic acid.

From Neurospora crassa.

pNPG-1(4-Nitrophenyl β-D-glucuronide) is a glucuronide monosaccharide derivative that is a chromogenic substrate for β-glucosidase.