alpha-L-fucosidase in cultured skin fibroblasts from normal subjects and fucosidosis patients

Abstract

alpha-L-Fucosidase (EC 3.2.1.51) activity was studied in cultured skin fibroblasts obtained from 23 members of a family in which two cases of fucosidosis type 2 had occurred and in the fibroblasts of a patient with fucosidosis type 1. Both the 4-methylumbelliferyl glycoside and the p-nitrophenyl derivative were used as substrates. pH activity profiles showed two major peaks of activity. With the fluorogenic substrate pH optimum was at 4.5, whereas with the colorigenic substrate maximum activity was at pH 5.7. No activity was found in the fibroblasts of the three patients with the colorimetric assay. With the fluorometric assay the mean activity in the two patients with fucosidosis type 2 was 4.1 and 2.8 (range 1.3-9.9); activity in the patient with fucosidosis type 1 was 4.6 nmol 4-methylumbelliferone/mg protein/hr (range 1.0-8.6). The specific activity in the lysates of the patients' fibroblasts decreased as the amount of cellular protein used per assay increased. Fucosidosis fibroblasts cultured for 3 and 5 days in medium without fetal calf serum showed almost the same levels of apparent residual activity as fibroblasts cultured in medium containing fetal calf serum. Maximum activity in the deficient fibroblasts was at pH 4.5-4.75. Mixing experiments between lysates of both of fucosidosis and a normal fibroblast strain showed the expected enzymatic activities. The mean alpha-fucosidase activity in four heterozygotes for fucosidosis was 37.6 (range 24.1-48.7) and 30.3 (range 19.0-44.1) nmol final product split/mg protein/hr with the fluorogenic and the colorigenic substrate, respectively. In 12 normal fibroblast strains the mean activity +/- SD was 85.3 +/- 24.4 (range 50.8-129.3) and 67.6 +/- 21.1 (range 31.1-118.3). However, in four family members in which the alpha-L-fucosidase phenotype (by isoelectric focusing) was type 2-1, and who should therefore be carrying two normal alleles, the activity was within the heterozygote range. This indicates that occasional overlap between normal subjects and carriers may be present in cultured skin fibroblasts. Increased specific activity of alpha-L-fucosidase at pH 3.2-4.0 was observed after incubation of cell lysates with neuraminidase. The alpha-L-fucosidase activity did not show any increase after fusion between fucosidosis fibroblasts type 1 and 2.