125Iodine labeling of beta-hexosaminidase A without modifying its properties

Human placental beta-hexosaminidase A was labeled with 125iodine to high specific activity with the retention of conformational integrity as judged by the retention of enzymatic activity. The oligosaccharide structure also appeared to be intact since the labeled enzyme was cleared from the circulation of the rat with a half-life identical to that of the unlabeled enzyme and an excess of unlabeled enzyme effectively blocked the clearance of the labeled form. Furthermore, the pattern of inhibition of clearance of the native and labeled enzymes by asialofetuin and mannans was identical. This useful and mild procedure for labeling enzymes may be of general importance in the preparation of enzymes for metabolic studies in normal animals and animal models of genetic lysosomal storage disorders.