Porcine thyroid fucosidase.

An alpha-L-fucosidase (alpha-L-fucoside fucohydrolase, EC 3.2.1.51) has been isolated from porcine thyroid tissue and purified 10,800-fold using a combination of ion exchange, affinity and molecular sieve chromatography. The enzyme appears homogeneous by SDS electrophoresis but isoelectric focusing procedures detect considerable heterogeneity. The enzyme is a glycoprotein and this fact interferes with accurate molecular weight estimates by SDS electrophoresis or molecular sieve techniques. The enzyme appears, however, to be a tetramer and density gradient measurements set its molecular weight at 192,000 +/- 3,000. The enzyme exhibits an optimum at a pH of 5.1 and shows a high order of specificity for L-fucose units linked through alpha bonds. Both sulfhydryl and carboxyl groups appear necessary for enzyme activity. The enzyme does not attack intact thyroglobulin directly but will remove fucosyl residues from the glycone moiety if the protein portion is largely removed. The enzyme thus functions in a salvage role as thyroglobulin is degraded.