Purification and characterization of lysosomal β-glucuronidase from human placenta

1. Subcellular fractions of human placenta were prepared by nitrogen-bomb homogenization and differential centrifugation. 2. beta-Glucuronidase from placental lysosomes was purified 2100-fold on a protein basis. 3. The lysosomal enzyme, at different stages of purification, was characterized by using 4-methylumbelliferyl beta-d-glucuronide and phenolphthalein beta-d-glucuronide as substrates. 4. Only one isoenzyme of beta-glucuronidase was found in placenta; the enzyme in the endoplasmic reticulum appeared to be the same as the lysosomal enzyme. 5. The isoenzyme contained in normal plasma was different from that of the placenta. 6. The elevated beta-glucuronidase activity found in plasma obtained during pregnancy was due to increased activity of the normal plasma isoenzyme; no contribution was made by placental isoenzyme. 7. Plasma contained a heat-stable, non-diffusible activator of placental beta-glucuronidase. 8. A heat-stable competitive inhibitor of placental and plasma beta-glucuronidase was also present in plasma.