Studies in metachromatic leukodystrophy. XIV. Purification and subunit structure of human liver arylsulfatase A

Arylsulfatase A was purified to apparent homogeneity from normal human livers obtained at autopsy. According to gel electrophoresis in sodium dodecyl sulfate, purified arylsulfatase A consistently contained two subunits of slightly different sizes: approximately 69 000 and 57 000 daltons, but were not present in stoichiometrically equal amounts. Peptide maps of the entire enzyme and of the two individual subunits showed that the two polypeptides share similar if not identical sequences. These observations raise the possibility that the smaller polypeptide might be derived from the larger one. The sensitive peptide mapping procedures employed will make feasible future studies with the abnormal enzyme found in metachromatic leukodystrophy.