Adenine-related compounds modulate UDP-glucuronosyltransferase (UGT) activity in mouse liver microsomes

Adenine-related compounds are allosteric inhibitors of UDP-glucuronosyltransferase (UGT) in rat liver microsomes (RLM) and human UGT isoforms treated with detergent or pore-forming peptide, alamethicin.To clarify whether the same is true beyond species, the effects of adenine-related compounds on 4-methylumbelliferone (4-MU) glucuronidation were examined using detergent-treated mouse liver microsomes (MLM).Brij-58 treatment of MLM increased the Vmax and the Michaelis constant, Km, of 4-MU. This study was performed using Brij-58-treated MLM as an enzyme source. ATP- and ADP-inhibited 4-MU glucuronidation. In contrast, AMP caused a 1.5-fold increase in glucuronidation. Oxidised forms, NAD+ and NADP+, potently inhibited 4-MU glucuronidation, whereas the reduced forms, NADH and NADPH, did not. Furthermore, the IC50 values of ATP, ADP, NAD+, and NADP+ were approximately 15 μM.In our previous study, ATP was the strongest inhibitor of UGT activity in RLM. However, in this study, the above-mentioned compounds inhibited 4-MU UGT in a comparable and noncompetitive manner. Furthermore, AMP antagonised the inhibitory effects of ATP and ADP.These results suggest that ATP, ADP, NAD+, and NADP+ are common endogenous inhibitors of UGT beyond species.