Glutamate dehydrogenase activity in crude plant extracts

The glutamate dehydrogenase deamination assay based on the increase of absorbance at 340 nm, caused by the transformation of NAD into NADH in the presence of L-giutamate applied to crude plant extracts, is unreliable without dialysis of the extract to eliminate disturbing reactions. A low molecular weight substance, probably a phenolic compound or aromatic amine, was isolated from Petunia leaves which could act as a substrate or activator of another dehydrogenase. This dehydrogenase which interferes with the glutamate dehydrogenase deamination assay may use many amino acids and amines as substrate. The use of a 1 % concentration of insoluble polyvinylpyrrolidone in the extraction buffer causes a higher glutamate dehydrogenase activity for both amination and deamination. The glutamate dehydrogenase is partially present in a latent form.