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

Abstract

1. 1. Bovine adrenal medulla dopamine β-hydroxylase, a glycoprotein with terminal mannose residues in the 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 shows either that more than one type of carbohydrate unit occurs on the protein or that three are multibranched chains in the carbohydrate moiety. 2. 2. Dopamine β-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 β-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 β-hydroxylase led to an increase of precipitation with ricin. The low extent of native human serum dopamine β-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 β-hydroxylases could be due to post-mortem effects. The clinical implications of possibility of differences concerning the carbohydrate moiety structures of pheochromocytoma and normal enzymes is discussed.