Intracellular Localization of Exogenous β‐Glucuronidase in Cultured Skin Fibroblasts

Abstract

The intracellular localization of exogenously supplied human platelet .beta.-glucuronidase [EC 3.2.1.31] in cultured skin fibroblasts derived from a .beta.-glucuronidase-deficient (mucopolysaccharidosis type VII) patient was studied. Four cellular fractions were obtained by differential speed centrifugation. Following 2 days of incubation, the exogenously supplied enzyme exhibited a distribution pattern identical to that of endogenous .beta.-hexosaminidase. Disruption of membranes by freezing and thawing caused a 35% increase of the enzyme activity, thus indicating a latent activity following the internalization. This indicated localization in the lysosomal fractions. Longer incubation periods led to an intracellular shift of the engulfed enzyme from the lighter lysosomal fraction to heavier particles. Once located in the heavier fraction, the enzyme was relatively stable, and participated in the catabolism of 35S-labeled mucopolysaccharides which had accumulated in the lysosomes of these fibroblasts. A marked reduction in the accumulated mucopolysaccharides of the lysosomal fraction was observed following addition of the enzyme. This was accompanied by the formation of smaller sized molecules.