Document Detail

Liver microsomal beta-glucuronidase and UDP-glucuronyltransferase.
MedLine Citation:
PMID:  230     Owner:  NLM     Status:  MEDLINE    
Both UDP-glucuronyltransferase (GT) and beta-glucuronidase (betaG) were assayed in untreated liver microsomes. Optimum assay conditions were established with rat liver microsomes using p-nitrophenol (pNP) and its glucuronide (pNPGA) at the pH optima of GT (7.5) and betaG (4.5). The activities of the two enzymes were compared using microsomes from rats, mice, pigs, cattle and horses, with pNP, pNPGA, and phenolphthalein as substrate, in the presence of various cofactors and inhibitors at pH 7.5 and 4.5. These data disclose pronounced differences with respect to species, substrate and other experimental conditions, thereby precluding the establishment of general optimum conditions. The two enzymes were also assayed under strictly identical conditions using pNP and pNPGA and rat liver microsomes at pH 7.5 in the presence and absence of UDP-glucuronate disodium (UDPGA), activators (ATP;UDP-N-acetylglucosamine) and inhibitors. When provided with a functional level of UDPGA, both enzymes proved active under those conditions, and a conjugation-deconjugation interplay was indicated. The two processes could be selectively and totally inhibited by Zn2+ and saccharolactone. The results suggest that conjugation-deconjugation-reconjugation cycles may be operative in the metabolism of drugs in vivo, taking place already at the level of the liver endoplasmic reticulum.
I Schöllhammer; D S Poll; M H Bickel
Publication Detail:
Type:  Journal Article    
Journal Detail:
Title:  Enzyme     Volume:  20     ISSN:  0013-9432     ISO Abbreviation:  Enzyme     Publication Date:  1975  
Date Detail:
Created Date:  1976-02-09     Completed Date:  1976-02-09     Revised Date:  2003-11-14    
Medline Journal Info:
Nlm Unique ID:  1262265     Medline TA:  Enzyme     Country:  SWITZERLAND    
Other Details:
Languages:  eng     Pagination:  269-76     Citation Subset:  IM    
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MeSH Terms
Adenosine Triphosphate / pharmacology
Cations, Divalent
Glucuronidase / metabolism*
Glucuronosyltransferase / metabolism*
Hexosyltransferases / metabolism*
Hydrogen-Ion Concentration
Lactones / pharmacology
Microsomes, Liver / enzymology*
Species Specificity
Sugar Alcohols / pharmacology
Uridine Diphosphate N-Acetylglucosamine / pharmacology
Zinc / pharmacology
Reg. No./Substance:
0/Cations, Divalent; 0/Lactones; 0/Sugar Alcohols; 528-04-1/Uridine Diphosphate N-Acetylglucosamine; 56-65-5/Adenosine Triphosphate; 7440-66-6/Zinc; EC 2.4.1.-/Hexosyltransferases; EC; EC

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine

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