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Membrane-bound estrone as substrate for microsomal UDP-glucuronyltransferase
The Journal of Biological Chemistry
|November 10, 1977
Summary
Microsomal membranes concentrate nonpolar substrates like estrone, enhancing UDP-glucuronyl-transferase activity. This membrane partitioning facilitates substrate orientation for efficient drug metabolism.
Area of Science:
- Biochemistry
- Pharmacology
- Cell Biology
Background:
- Microsomal UDP-glucuronyl-transferase (UGT) enzymes metabolize xenobiotics.
- Nonpolar substrates partition between aqueous and lipid phases.
Purpose of the Study:
- To investigate the role of microsomal membranes in concentrating nonpolar substrates.
- To determine if membrane-bound substrates are preferentially utilized by UGT.
Main Methods:
- Measuring estrone partitioning into microsomal membranes.
- Comparing estrone conjugation rates with its release rate from membranes.
- Assessing glucuronidation rates at varying estrone concentrations in the aqueous phase.
Main Results:
- Estrone partitioning into microsomes was extensive.
- The rate of estrone conjugation was significantly higher (6-fold) than its release rate.
- Estrone glucuronidation rate was independent of estrone concentration in the bulk aqueous phase.
Conclusions:
- Microsomal membranes concentrate nonpolar UGT substrates, increasing their availability for catalysis.
- Membrane phospholipids may act as co-factors by orienting substrates to facilitate UGT activity.