Latency is the major determinant of UDP-glucuronosyltransferase activity in isolated hepatocytes.
The glucuronidation of p-nitrophenol was measured in intact, saponin- and alamethicin-treated isolated mouse hepatocytes. In saponin-permeabilized cells the elevation of extrareticular UDP-glucuronic acid concentration enhanced the rate of glucuronidation threefold. When intracellular membranes were also permeabilized by alamethicin, a further tenfold increase in the glucuronidation of p-nitrophenol was present. Parallel measurements of the ER mannose 6-phosphatase activity revealed that saponin selectively permeabilized the plasma membrane, whereas alamethicin permeabilized both plasma membrane and ER membranes. The inhibition of p-nitrophenol glucuronidation by dbcAMP in intact hepatocytes was still present in saponin-treated cells and disappeared in alamethicin-permeabilized hepatocytes. It is suggested that the permeability of the endoplasmic reticulum membrane is a major determinant of glucuronidation not only in microsomes but in isolated hepatocytes as well.
1st Institute of Biochemistry, Semmelweis Medical University, Budapest, Hungary.
G
G
Bánhegyi
T
T
Garzó
R
R
Fulceri
A
A
Benedetti
J
J
Mandl
D000408:Alamethicin / Q000494:pharmacology; D000818:Animals; D002463:Cell Membrane Permeability / Q000187:drug effects; D004721:Endoplasmic Reticulum / Q000187:drug effects / Q000201:enzymology; D014453:Glucuronosyltransferase / Q000378:metabolism*; D008099:Liver / Q000187:drug effects / Q000201:enzymology*; D008297:Male; D051379:Mice; D009596:Nitrophenols / Q000378:metabolism; D010744:Phosphoric Monoester Hydrolases / Q000378:metabolism; D012503:Saponins / Q000494:pharmacology; D014535:Uridine Diphosphate Glucuronic Acid / Q000378:metabolism
D009596:Nitrophenols; D012503:Saponins; D014535:Uridine Diphosphate Glucuronic Acid; D000408:Alamethicin; D014453:Glucuronosyltransferase; C023553:mannose-6-phosphatase; D010744:Phosphoric Monoester Hydrolases; C024836:4-nitrophenol