Studies on the interaction of dopamine beta-hydroxylase from various sources with phytohaemagglutinins

1. Bovine adrenal medulla dopamine beta-hydroxylase, a glycoprotein with terminal mannose residues in carbohydrate moiety, did not precipitate with any lectins tested except concanavalin A. After digestion with neuraminidase, the enzyme was shown to interact with ricin, and a good correlation was found between the amount of liberated sialic acids and the extent of agglutination. This finding show either that more than one type of carbohydrate unit occurs on the protein or that three are multibranched chains in the carbohydrate moiety. 2. Dopamine beta-hydroxylase from human serum, pheochromocytoma and normal adrenal were incubated with concanavalin A, ricin, wheat germ agglutinin and lectins from Dilochos biflorus and Robinia pseudoacacia. 83% of dopamine beta-hydroxylase from pheochromocytoma was precipitated by ricin, whereas the enzyme from human serum precipitated to a lesser extent (5-15%). Neuraminidase digestion of human serum dopamine beta-hydroxylase led to an increase of precipitation with ricin. The low extent of native human serum dopamine beta-hydroxylase precipitation with ricin can be explained by the attack of plasma membrane sialidases of liver cells, whereas the greater ricin precipitation of pheochromocytoma and normal adrenal dopamine beta-hydroxylases could be due to post-mortem effects. The clinical implications of possibility of difference concerning the carbohydrate moiety structures of pheochromocytoma and normal enzymes is discussed.