Variability of human hepatic UDP-glucuronosyltransferase activity.
The availability of a unique series of liver samples from human subjects, both control patients (9) and those with liver disease (6; biliary atresia (2), retransplant, chronic tyrosinemia type I, tyrosinemia, Wilson's disease) allowed us to characterize human hepatic UDP-glucuronosyltransferases using photoaffinity labeling, immunoblotting and enzymatic assays. There was wide inter-individual variation in photoincorporation of the photoaffinity analogs, [32P]5-azido-UDP-glucuronic acid and [32P]5-azido-UDP-glucose and enzymatic glucuronidation of substrates specific to the two subfamilies of UDP-glucuronosyltransferases. However, the largest differences were between subjects with liver disease. Glucuronidation activities toward one substrate from each of the UDP-glucuronosyltransferases subfamilies, 1A and 2B, for control and liver disease, respectively, were 1.7-4.5 vs 0.4-4.7 nmol/mg x min for hyodeoxycholic acid (2B substrate) and 9.2-27.9 vs 8.1-75 nmol/mg x min for pchloro-m-xylenol (1A substrate). Microsomes from a patient with chronic tyrosinemia (HL32) photoincorporated [32P]5-azido-UDP-glucuronic acid at a level 1.5 times higher than the other samples, was intensely photolabeled by [32P]5-azido-UDP-glucose and had significantly higher enzymatic activity toward p-chloro-m-xylenol. Immunoblot analysis using anti-UDP-glucuronosyltransferase antibodies demonstrated wide inter-individual variations in UDP-glucuronosyltransferase protein with increased UDP-glucuronosyltransferase protein in HL32 microsomes, corresponding to one of the bands photolabeled by both probes. Detailed investigation of substrate specificity, using substrates representative of both the 1A (bilirubin, 4-nitrophenol) and 2B (androsterone, testosterone) families was carried out with HL32, HL38 (age and sex matched control) and HL18 (older control). Strikingly increased (5-8-fold) glucuronidation activity was seen in comparison to HL18 only with the phenolic substrates. The results indicate that one or more phenol-specific UDP-glucuronosyltransferase 1A isoforms are expressed at above normal levels in this tyrosinemic subject.
Little
J M
JM
Department of Biochemistry and Molecular Biology, University of Arkansas for Medical Sciences, Little Rock 72205, USA.
Lester
R
R
Kuipers
F
F
Vonk
R
R
Mackenzie
P I
PI
Drake
R R
RR
Frame
L
L
Radominska-Pandya
A
A
D000293:Adolescent; D000328:Adult; D002648:Child; D002675:Child, Preschool; D005260:Female; D014453:Glucuronosyltransferase / Q000378:metabolism*; D006801:Humans; D008297:Male; D008862:Microsomes, Liver / Q000201:enzymology*; D008875:Middle Aged; D019920:Photoaffinity Labels; D014443:Tyrosine / Q000097:blood
D019920:Photoaffinity Labels; D014443:Tyrosine; D014453:Glucuronosyltransferase