title: Ascorbic acid deficiency and hepatic UDP-glucuronyl transferase. Qualitative and quantitative differences.
abstract: The effect of dietary ascorbate on hepatic UDP glucuronyltransferase (UDPGT) appears to be selective in that only certain isozymes of UDPGT are jeopardized. In this study, ascorbic acid deficiency produced a 68% reduction in the specific activity of hepatic UDPGT towards p-nitrophenol. Earlier studies showed a reduction in UDPGT activity towards p-aminophenol in ascorbate-deficient guinea pigs, whereas bilirubin and acetaminophen glucuronidation were unaffected. Kinetic studies suggest that p-aminophenol and p-nitrophenol are metabolized by a single isozyme in that p-nitrophenol was found to be a competitive inhibitor of p-aminophenol glucuronidation. Both qualitative and quantitative studies on partially purified UDPGT from ascorbate-deficient and ascorbate-supplemented guinea pigs were carried out to investigate the biochemical role of the vitamin. Qualitative differences were observed in UDPGT from ascorbate-deficient animals and included an increased lability to: thermal inactivation; storage at 4 degrees; and purification with UDP-glucuronic acid agarose column chromatography. Furthermore, an analysis of the microsomal membrane showed a 14% increase in membrane fluidity in ascorbate deficiency. Ascorbic acid added in vitro could not reverse the increase in fluidity observed in ascorbate-deficient microsomal membranes; however, ascorbylpalmitate, a more lipophilic form of the vitamin, was effective. Palmitic acid had no effect on membrane fluidity in microsomes from either the ascorbate-supplemented or ascorbate-deficient animals. This increase in membrane fluidity could not be explained by differences in cholesterol, total phospholipid, or phosphatidylcholine content of hepatic microsomes. Furthermore, a quantitative reduction in UDPGT partially purified from ascorbate-deficient guinea pigs was indicated by a marked reduction in protein banding at 55,000 daltons when compared to UDPGT partially purified from ascorbate-supplemented animals.
authors.affiliation: Department of Pharmacology, University of Michigan, Ann Arbor 48109.
authors.forename: C M
authors.initials: CM
authors.lastname: Neumann
authors.forename: V G
authors.initials: VG
authors.lastname: Zannoni
mesh_terms: D000818:Animals; D001205:Ascorbic Acid / Q000494:pharmacology; D001206:Ascorbic Acid Deficiency / Q000201:enzymology*; D002855:Chromatography, Thin Layer; D004591:Electrophoresis, Polyacrylamide Gel; D004795:Enzyme Stability / Q000187:drug effects; D014453:Glucuronosyltransferase / Q000302:isolation & purification / Q000378:metabolism*; D006168:Guinea Pigs; D006358:Hot Temperature; D007425:Intracellular Membranes / Q000187:drug effects / Q000378:metabolism; D008099:Liver / Q000187:drug effects / Q000201:enzymology*; D008560:Membrane Fluidity / Q000187:drug effects; D008862:Microsomes, Liver / Q000187:drug effects / Q000378:metabolism
chemical_list: D014453:Glucuronosyltransferase; D001205:Ascorbic Acid