Isoenzymes of human liver ?-L-fucosidase: Chemical relationship, kinetic studies, and immunochemical characterization

Abstract

The chemical relationship of the seven forms of human liver α-L fucosidase has been studied by isoelectric focusing of neuraminidase- and sialyltransferase-treated preparations of α-L-fucosidase. Neuraminidase treatment leads to a decrease in the activity of the more acidic forms (IV–VII) and a concomitant increase in the activity of the more neutral forms (I–II). Incubation of the neuraminidase-treated fucosidase (forms I–III) with radiolabelled cytidine monophosphate-N-³H-acetylneuraminic acid and an enriched preparation of sialyltransferase devoid of fucosidase activity led to regeneration of the more acidic fucosidase isoenzymes (IV–VII) with the same isoelectric points and in nearly the same proportion as before neuraminidase treatment. These experiments suggest that the isoenzymes of human liver α-L-fucosidase are related, at least in part, by sialic acid residues. The seven isoenzymes of purified human liver α-L-fucosidase have been separated by preparative isoelectric focusing and characterized kinetically and immunochemically. Differences in Michaelis constants (Km's) and pH optimum curves were found for some of the isoenzymes. All seven isoenzymes were immunoprecipitated using the IgG fraction of anti-α-L-fucosidase antiserum suggesting that the presence of sialic acid residues does not affect the antigenicity of the forms of α-L-fucosidase.