Dietary lipid regulates the amount and functional state of UDP- glucuronosyltransferase in rat liver

The effect of a fat-free diet on the amount and functional state of UDP- glucuronosyltransferase was studied in rat liver microsomes. Measurements of enzyme activity showed that activity was ~30% lower in untreated microsomes in response to the fat-free diet as compared with the control diet. Immunoblotting with anti-UDP-glucuronosyltransferase showed ~200% less enzyme in rats fed the fat-free diet. A kinetic method for measuring total UDP-glucuronosyltransferase confirmed the result of the immunoblot. Thus, the total amount of enzyme declined to a greater extent than enzyme activity. Responses of the enzyme to activation by palmitoyl-lysophosphatidylcholine or UDP-N-acetylglucosamine suggested that rats fed the fat-free diet had a greater activity per molecule of UDP-glucuronosyltransferase than did rats fed the control diet. This result explained the relatively small decline in enzyme activity as compared with enzyme concentration in microsomes prepared from animals fed the fat-free diet. Fatty acid analysis of microsomal lipids demonstrated that the fat-free diet was associated with lower levels of arachidonic and linoleic acids and greater amounts of palmitoleic, oleic and cis-vaccenic acids.