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Beta-glucuronidase latency in isolated murine hepatocytes
1Department of Medical Chemistry, Semmelweis University of Medicine, Budapest, Hungary.
Biochemical Pharmacology
|March 16, 2000
Summary
Microsomal beta-glucuronidase likely does not process external glucuronides. Its role may involve internal endoplasmic reticulum (ER) substrate hydrolysis for ascorbate synthesis or glucuronidation proofreading.
Area of Science:
- Biochemistry
- Cell Biology
- Enzymology
Background:
- The physiological role of microsomal beta-glucuronidase remains largely unknown.
- Potential substrates include lumenal endoplasmic reticulum (ER) glucuronides or hepatocyte-taken-up glucuronides.
- Efficient transport across cellular membranes is necessary for external substrate access.
Purpose of the Study:
- To investigate the potential role of beta-glucuronidase within the ER.
- To determine if liver microsomal beta-glucuronidase processes external glucuronides.
Main Methods:
- Experiments utilized isolated mouse hepatocytes and liver microsomal vesicles from mice and rats.
- Selective permeabilization of hepatocyte plasma and ER membranes was performed using saponin, digitonin, and Triton X-100.
- Enzyme activity and substrate permeability were assessed using p-nitrophenol glucuronide, phenolphthalein glucuronide, and light scattering.
Main Results:
- Permeabilization of hepatocyte membranes significantly increased glucuronide hydrolysis rates.
- Microsomal vesicles exhibited approximately 50% latency in beta-glucuronidase activity.
- Microsomes demonstrated low permeability to both glucuronides and glucuronate.
Conclusions:
- Liver microsomal beta-glucuronidase is unlikely to be involved in deconjugating glucuronides taken up by hepatocytes.
- The enzyme may hydrolyze glucuronides synthesized within the ER lumen.
- This internal hydrolysis could supply substrates for ascorbate synthesis or function in glucuronidation proofreading.