Luminal accumulation of newly synthesized morphine-3-glucuronide in rat liver microsomal vesicles

Katalin Révész, Blanka Tóth, Adam G. Staines, Michael W H Coughtrie, J. Mandl, M. Csala

Research output: Contribution to journalArticle

4 Citations (Scopus)

Abstract

Morphine is converted to morphine 3-β-D-glucuronide (M3G) by the UDP-glucuronosyltransferase Ugt2b1 in the endoplasmic reticulum (ER) of rat liver. Because of its luminal localization, UGT activity requires UDP-glucuronate import and glucuronide export across the ER membrane. The former transport is generally considered to be rate limiting and to explain the latency of UGT activities in intact microsomal vesicles. However, some observations indicate that the release of bulky glucuronides, such as M3G, might also be rate limiting for glucuronidation. This assumption was tested by characterizing the transport of M3G and its distribution between the intra- and extravesicular spaces during synthesis in rat liver microsomes. The amount of vesicle-associated M3G was measured using rapid filtration and LC-MS measurement. Our results reveal a remarkable accumulation of newly synthesized M3G in the microsomal lumen above the equilibrium. The transport showed a linear concentration-dependence in a wide range (5-200 μM). Therefore, the build-up of high (about 20 μM) luminal M3G concentration could adjust the rate of release to that of synthesis (44.85 ± 4.08 pmol/min/mg protein) during the conjugation of 100 μM morphine. These data can explain earlier findings indicative of separate intracellular pools of M3G in rat liver. Accumulation of bulky glucuronides in the ER lumen might also play an important role in their targeting and in the control of biliary excretion.

Original languageEnglish
Pages (from-to)271-278
Number of pages8
JournalBioFactors
Volume39
Issue number3
DOIs
Publication statusPublished - May 2013

Fingerprint

Glucuronides
Liver
Rats
Morphine
Endoplasmic Reticulum
Glucuronosyltransferase
Glucuronic Acid
Uridine Diphosphate
Liver Microsomes
morphine-3-glucuronide
Membranes
Proteins

Keywords

  • Endoplasmic reticulum
  • Excretion
  • Glucuronide
  • Morphine
  • Transport

ASJC Scopus subject areas

  • Biochemistry
  • Clinical Biochemistry
  • Molecular Medicine

Cite this

Luminal accumulation of newly synthesized morphine-3-glucuronide in rat liver microsomal vesicles. / Révész, Katalin; Tóth, Blanka; Staines, Adam G.; Coughtrie, Michael W H; Mandl, J.; Csala, M.

In: BioFactors, Vol. 39, No. 3, 05.2013, p. 271-278.

Research output: Contribution to journalArticle

Révész, Katalin ; Tóth, Blanka ; Staines, Adam G. ; Coughtrie, Michael W H ; Mandl, J. ; Csala, M. / Luminal accumulation of newly synthesized morphine-3-glucuronide in rat liver microsomal vesicles. In: BioFactors. 2013 ; Vol. 39, No. 3. pp. 271-278.
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