GLYCOSIDASE ACTIVITY OF BOVINE LIVER PLASMA MEMBRANES

1. 1. Plasma membranes were isolated on a large scale from bovine liver by a modified method of Neville1. They were characterized with respect to contamination by endoplasmic reticulum, lysosomes, and mitochondria. 2. 2. The membranes were found to contain glycosidases capable of hydrolyzing uridine diphosphogalactose (UDP-Gal) and uridine diphosphoglucose as well as o-nitrophenyl α- or β-galactosides. 3. 3. The hydrolysis of UDP-Gal using a 14C-labeled substrate in the galactose moiety allowed a rapid estimation of the amount of plasma membrane contaminating microsomal fractions. Smooth microsomes were contaminated about 14% with plasma membranes. This value agreed with estimates based on the content of Mg2+-stimulated ATPase and of 5′-nucleotidase. Rough microsomes contained about 5% plasma membranes using this criterion. Purified nuclei and mitochondria from bovine liver showed negligible amounts of this activity. 4. 4. The optimum pH of the enzyme was 7.2 using cacodylate buffer. Mg2+ stimulated the activity slightly whereas Mn2+ was inhibitory. The Km for UDP-Gal was 0.33 mM. © 1969.