Sulfogalactosylsphingosine Sulfatase CHARACTERISTICS OF THE ENZYME AND ITS DEFICIENCY IN METACHROMATIC LEUKODYSTROPHY IN HUMAN CULTURED SKIN FIBROBLASTS

Abstract Sulfogalactosylsphingosine sulfatase activity was demonstrated in cultured human skin fibroblasts using 35S-labeled sulfogalactosylsphingosine as the substrate. The pH optimum of the enzyme was 4.5. The reaction was linear up to 2 hours and the rate was proportional to the amount of enzyme added. The Km of the enzyme was 3.32 x 10-4 m. Taurodeoxycholate, taurocholate, deoxycholate, and cholic acid stimulated enzyme activity. Taurodeoxycholate had the greatest effect. Tween 80 and Triton X-100 had no effect. Mn2+ increased the enzyme activity 2-fold, whereas Hg2+, Cu2+, Ba2+, and Zn2+ were all inhibitory. The isoelectric point of the enzyme, determined by isoelectric focusing, was 4.8. Sulfogalactosylceramide was a competitive inhibitor with an inhibition constant of 0.2 x 10-3 m. The above properties and kinetics of sulfogalactosylsphingosine sulfatase were identical with those of sulfogalactosylceramide sulfatase except for minor differences in the effects of detergents and ions. Both enzymes were deficient in fibroblasts from patients with classical metachromatic leukodystrophy or with a variant form of metachromatic leukodystrophy characterized by multiple sulfatase deficiencies. These findings suggest that the same enzyme may be capable of degrading both sulfogalactosylsphingosine and sulfogalactosylceramide. The implication of this observation in relation to the degradation of sulfogalactosylceramide and to the pathogenesis of metachromatic leukodystrophy is discussed.