pH-Dependent association-dissociation of high and low activity plasma a-l-fucosidase

Summary Population and family studies have confirmed the existence of a plasma a-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 plasma a-l-fucosidase is heat-inactivated at acidic pH. Sucrose gradient centrifugation results indicate the transition of non-variant plasma a-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 variant a-l-fucosidase monomer is not converted into a trimer, but only partially into a dimer.