[Studies on charge heterogeneity of arylsulfatase A from human lung cancer]

Arylsulfatase A was purified from human lung and human placenta to apparent homogeneity presented by electrophoresis in the absence and presence of sodium dodecyl sulfate. The enzyme from normal lung, placenta, and lung adenocarcinoma showed considerable charge heterogeneity when examined by isoelectrofocusing, with isoelectric point (pI) ranging from 5.1 to 4.6. The enzyme from adenocarcinoma was more heterogeneous and having more acidic components than the other enzyme. When the tumor enzyme was treated with exogenous sialidase, alkaline phosphatase, or endo-beta-N-acetylhexosaminidase H (endoglycosidase H), the acidic components of the enzyme shifted to the more alkaline region on the focussing gel. The banding pattern of the enzyme from normal tissues also changed to the more alkaline region when treated with exogenous hydrolase and showed almost the same pattern as hydrolase treated enzyme from adenocarcinoma. Combined treatment of the enzyme with endoglycosidase H and sialidase resulted in complete loss of the most acidic components to give the less acidic components with pI of 5.1.50. and 4.9. Cyclic AMP-dependent protein kinase could not phosphorylate the protein moiety of arylsulfatase A even after the enzyme was treated with alkaline phosphatase. When an acidic fraction of the endoglycosidase H sensitive oligosaccharides from arylsulfatase A was treated with phosphatase, the acidic oligosaccharide fraction lost the negative charge on QAE-Sephadex chromatography. These results strongly suggest that the charge heterogeneity of arylsulfatase A is due not only to sialylation but also to phosphorylation at the carbohydrate moiety of the enzyme, and that the extent of substitution by acidic groups, sialic acid residue and phosphate residue, is markedly increased in the tumor enzyme.