Population and family studies have confirmed the existence of a plasmaa-l-fucosidase polymorphism in humans and the autosomal recessive inheritance of the low activity trait. The frequency of the latter is estimated at 11. The low activity individuals or variants can also be distinguished by the fact that their plasmaa-l-fucosidase is heat-inactivated at acidic pH. Sucrose gradient centrifugation results indicate the transition of non-variant plasmaa-l-fucosidase with a molecular weight of 66,000 at pH 8.4 to an enzyme form with a molecular weight of 193,000 at pH 3.0. The former is thermolabile, the latter thermostable. Interconversion is pH-dependent. It is hypothesized that the non-variant enzyme, a monomer at alkaline pH, changes upon acidification into a trimeric conformation via dimerization. The thermolabile varianta-l-fucosidase monomer is not converted into a trimer, but only partially into a dimer.
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