Plasma alpha-L-fucosidase: presence of a low activity variant in some normal individuals.

The expression of a variant alpha-L-fucosidase has been determined in both plasma and leukocytes. This variant enzyme is characterized by unusually tow actuvity in plasma, an altered pH activity profile, and increased heat lability. Individuals possessing this low activity variant in plasma have usual levels of alpha-L-fucosidase activity in leukocytes. The leukocyte enzyme also shows increased heat lability and has an altered pH activity profile. Gel filtration of plasma alpha-L-fucosidase revealed both a high molecular weight form, alpha-L-fucosidase I, and a low molecular weight form, alpha-L-fucosidase II. Only alpha-L-fucosidase II could be detected upon gel filtration of the variant enzyme from plasma. Both control and variant leukocyte alpha-L-fucosidase revealed two peaks by gel filtration but the proportion of alpha-L-fucosidase I was reduced in the variant enzyme sample. Alpha-L-fucosidase II from both control and variant plasma and leukocyte samples was heat labile and possessed little activity at pH 4.0 Alpha-L-fucosidase I from control plasma and leukocytes was more stable to heating and possessed more activity at pH 4.0 than alpha-L-fucosidase II. In contrast, alpha-L-fucosidase I from the variant leukocyte sample was heat labile and had little activity at pH 4.0 thus resembling alpha-L-fucosidase II. These results suggest that the variant is the consequence of an altered allele which affects alpha-L-fucosidase expression in all tissues.