Indications for post-translational regulation of Vitis vinifera L. arginine decarboxylase

In order to study arginine decarboxylase regulation, we produced an antiserum against a hybrid of a 615 amino acid residue fragment of grapevine arginine decarboxylase cDNA with maltose-binding protein. The antiserum generated recognized mainly a protein band of ca. 80 kDa in extracts from grapevine tissues. Extracts from leaves and internodes in different developmental stages showed differences in the quantity of the 80 kDa band recognized by the antiserum. However, these differences did not correspond with changes in arginine decarboxylase specific activity. Furthermore, western blot analysis of extracts from cell cultures, where enzyme-specific activity was induced or repressed, did not reveal respective changes in the quantity of the 80 kDa protein band. Digestion of the hybrid by the specific protease factor Xa resulted in a polypeptide of 90 kDa instead of the expected two polypeptides of 43 and 66 kDa. Finally, western blot analysis of shoot extract incubated with factor Xa or the hybrid protein previously digested by factor Xa revealed that factor Xa-digested hybrid protein cleaved the 80 kDa band, resulting in two bands of ca. 38 and 40 kDa, whereas factor Xa alone did not affect it. These results suggest that arginine decarboxylase protein levels and/or activity is post-translationally regulated, as has been shown for other enzymes of polyamine biosynthesis.