In vitro expression of alpha-L-fucosidase activity polymorphism observed in plasma

Several quantitative and qualitative characteristics of alpha-L-fucosidase were studied in cultured skin fibroblasts derived from variant and non-variant individuals. In comparison with non-variant cultures with similar growth characteristics, the intracellular level of alpha-L-fucosidase was specifically reduced by at least 50% at all stages of the culture cycle. The amount of enzyme released into the growth medium was also decreased, but the ratio of the extracellular enzyme to the total enzyme activity produced, was not significantly different from that in non-variant cultures. pH-dependence, apparent Km value and temperature sensitivity of the variant alpha-L-fucosidase were identical to that of the enzyme in non-variant cells. Specific differences between the variant and non-variant enzyme were consistently observed upon enzyme inactivation at acid pH and in thermostabilisation studies with NaCl. The DEAE elution profiles and pH-dependent association patterns obtained by ultracentrifugation were also different for both types of intracellular alpha-L-fucosidase. It is concluded that the quantitative as well as the qualitative differences of alpha-L-fucosidase characteristics found in variant fibroblasts are the in vitro expression of the variant genotype, already phenotypically observed in human plasma.