Turnover of murine beta-glucuronidase. Comparison among liver, kidney, and spleen and between lysosomes and microsomes

The turnover properties of murine beta-glucuronidase in several tissues and at two subcellular sites have been determined by monitoring the radioactivity present in immunoprecipitated enzyme at a number of time points following the in vivo administration of a single radiolabeled protein precursor (either L-[3,4(-3H)]leucine or or NaH14CO3). In all experiments a considerable period of time was required for the attainment of maximum specific radioactivity in glucuronidase. Similar labeling kinetics was found when [3H]leucine incorporation was monitored in immunoprecipitated murine liver delta-aminolevulinate dehydratase. Half-life estimates of 2 to 3 days were obtained for glucuronidases of liver, kidney, and spleen. In most strains of inbred mice, it is known that approximately 60% of total liver glucuronidase activity resides in lysosomes, while 40% is within the membranes of the endoplasmic reticulum (Ganschow, R. E. and Paigen, K. (1968) Genetics 59, 335-349). These two subcellular forms of glucuronidase turn over at similar rates. Furthermore, the bulk of glucuronidase in the endoplasmic reticulum does not serve as precursor to lysosomal glucuronidase.