Competition between p-aminophenol, p-nitrophenol, and bilirubin for glucuronidation in cultures of rat hepatoma cells and homogenates of the same cells.

: Glucuronidation of p-aminophenol (PAP), p-nitrophenol (PNP), and bilirubin has been studied in cultures of a clonal cell line with liver-like functions and homogenates from the same cells. The purpose was to study the effect of simultaneous addition of substrates to cultures of living cells and to homogenates with an excess of UDPGA, and to compare the glucuronidation rates in living cells and in homogenates from the same cells, fortified with UDPGA. The rates of glucuronidation of PAP, PNP, and bilirubin by cells in culture were about 50, 70, and 15 nmol/mg protein/hour respectively. In fortified cell homogenates the respective glucuronidation rates were about 500, 1800, and 15 nmol/mg protein/hour. PNP inhibited the glucuronidation of PAP and bilirubin both in cell cultures and cell homogenates. PAP inhibited the glucuronidation of bilirubin in cell cultures. Bilirubin did not inhibit the glucuronidation of the other substrates. PNP glucuronide did not inhibit the glucuronidation of bilirubin or PAP in cell cultures or homogenates.