Human leukocyte and plasma beta-D-fucosidase: identity with beta-D-galactosidase.

Our results of the study of the human leukocyte and plasma beta-fuc show that it is possible to measure the enzyme, although enzyme activity is low and long incubation times are necessary for the plasma enzyme. We were interested to know if beta-gal and beta-fuc are enzyme activities of a single protein. For the leukocytes, our observations on enzyme inhibition by galactonic acid-y-lactone and derivatives of beta-D-galactose, together with an enzyme deficiency in GM1 gangliosidosis confirm the previous observation that beta-fuc and beta-gal are enzyme activities of a single protein (5). In plasma, the high correlation coefficient, similar thermoinactivation profiles of beta-gal and beta-fuc, the inactivation of the two enzymes by beta-D-galactopyranosylmethyl-p-nitrophenyltriazene, and inhibition of beta-fuc by galactonic acid-y-lactone and paranitrophenyl-beta-D-galactose strongly suggest that beta-gal and beta-fuc are enzyme activities of a common protein. Because of the very low specific activities, we do not recommend the determination of beta-fuc in leukocytes or plasma for the biochemical diagnosis of GM1 gangliosidosis.