Evidence for the intraluminal positioning of p-nitrophenol UDP-glucuronosyltransferase activity in rat liver microsomal vesicles

Arch Biochem Biophys. 1994 Feb 15;309(1):43-6. doi: 10.1006/abbi.1994.1081.

Abstract

Addition of p-nitrophenol and UDP-glucuronic acid to rat hepatic microsomes enhanced the MgATP-stimulated Ca2+ sequestration. This stimulatory effect was more explicit in the presence of the activator of glucuronidation, UDP-N-acetylglucosamine. The stimulation of Ca2+ uptake was dependent on the p-nitrophenol concentration and showed a good correlation with the rate of p-nitrophenol glucuronidation. The stimulation of Ca2+ sequestration was probably due to its coaccumulation with the intraluminar Pi originated during glucuronidation. The increase in extravesicular osmolarity due to the addition of UDP-glucuronic acid to microsomes resuspended in an hyposmotic medium caused a rapid and prolonged shrinking as revealed by light-scattering measurements. This indicates a poor permeability of microsomal membrane to UDP-glucuronic acid. The subsequent addition of the pore-forming compound alamethicin resulted in an immediate swelling of vesicles indicating a rapid entry of UDP-glucuronic acid. Alamethicin also caused an about 15-fold increase in p-nitrophenol UDP-glucuronosyltransferase activity. These results support the hypothesis of the intravesicular compartmentation of the microsomal UDP-glucuronosyltransferase catalytic site.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adenosine Triphosphate / pharmacology
  • Alamethicin / pharmacology
  • Animals
  • Binding Sites
  • Calcium / metabolism
  • Enzyme Activation / drug effects
  • Glucuronosyltransferase / metabolism*
  • Male
  • Microsomes, Liver / drug effects
  • Microsomes, Liver / enzymology*
  • Nitrophenols / metabolism*
  • Nitrophenols / pharmacology
  • Rats
  • Rats, Sprague-Dawley
  • Uridine Diphosphate Glucuronic Acid / metabolism
  • Uridine Diphosphate Glucuronic Acid / pharmacology

Substances

  • Nitrophenols
  • Uridine Diphosphate Glucuronic Acid
  • Alamethicin
  • Adenosine Triphosphate
  • Glucuronosyltransferase
  • Calcium
  • 4-nitrophenol