Biosynthesis and maturation of arylsulfatase B in normal and mutant cultured human fibroblasts.

The biosynthesis of arylsulfatase B in normal and mutant human skin fibroblasts was studied by metabolic labeling with radioactive amino acids, monosaccharides, or 32Pi and by specific immunoprecipitation followed by polyacrylamide gel electrophoresis and fluorography. Three major polypeptides with apparent molecular weights of 47,000, 40,000, and 31,000 were found intracellularly and one of 64,000 in the medium. Pulse-chase labeling and uptake experiments showed that arylsulfatase B synthesized and secreted as a 64,000 precursor was intracellularly processed within less than 24 h via short lived intermediates to two different forms. Form I (chains of 47,000 and 11,500) was labeled earlier and was about twice as stable as form II (chains of 40,000 and 31,000). The secreted 64,000 precursor and the 40,000 chain of form II contained oligosaccharides resistant to endo-beta-N-acetylglucosaminidase H. In the other chains mainly cleavable and phosphorylated oligosaccharides were found. Arylsulfatase B activity was associated with the 64,000 precursor and with form I, but not with form II. Fibroblasts of four patients with the severe form of mucopolysaccharidosis type VI, which were deficient in arylsulfatase B activity, synthesized and secreted the 64,000 precursor at a normal rate. This precursor, however, had little if any catalytic activity and one of its mature forms (I) was rapidly degraded.