Abstract
p-Nitrophenol (PNP) sulfate conjugation in rat liver cytosol fraction was investigated over a wide PNP concentration range (1.25 μM-5 mM). The PNP sulfate synthesis rate in the liver cytosol decreased in the low PNP concentration range (10-500 μM) and increased again at concentrations above approximately 500 μM, as was previously found in isolated liver cells (J. Pharm. Dyn., 5, 811 (1982)). This apparent substrate at low PNP concentration was found in the sulfotransferase reaction when the cosubstrate, 3'-phosphoadenosine-5'-phosphosulfate (PAPS), had been generated in advance as well as in the overall reaction (i.e., including the generation process of PAPS), suggesting that the inhibition was due to direct interaction between PNP and aryl sulfotransferase, and not to inhibition of PAPS generation by PNP.
