Lipid solubility and affinity for N-demethylation of dansylamides in isolated rat hepatocytes

Isolated hepatocytes carry out the N-demethylation of dansylamide at near linear rates for up to 8 h. This reaction was measured by following the release of tritium into water on hydroxylation of 3H-labeled methyl groups. The competitive inhibition of dansylamide by dansylated amino acids was studied in this system as an example of competing drug metabolism in a series of compounds which are identical around the site of metabolism and different remote to that site. A correlation between lipid solubility and the Ki was not found over the entire range of substrate analogues. While most of the high Km inhibitors seem to correlate with lipid solubility, the highly lipophilic derivatives of the leucines and phenylalanine are in a separate group. Lipid solubilities of the dansylated amino acids were little affected by changes in pH and thus behaved as "essential nonelectrolytes".