Isoenzymes of human liver alpha-L-fucosidase: chemical relationship, kinetic studies, and immunochemical characterization.

The chemical relationship of the seven forms of human liver alpha-L fucosidase has been studied by isoelectric focusing of neuraminidase- and sialytransferase-treated preparations of alpha-L-fucosidase. Neuraminidase treatment leads to a decrease in the activity of the more acidic forms (IV-VII) and a concimitant 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 sialytransferase 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 alpha-L-fucosidase are related, at least in part, by sialic acid residues. The seven isoenzymes of purified human liver alpha-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-alpha-L-fucosidase antiserum suggesting that the presence of sialic acid residues does not affect the antigenicity of the forms of alpha-L-fucosidase.