The role of the anionic groups in the receptor binding of interleukin-8 antagonists

In an effort to determine the role of the acidic group in the receptor binding of N-(2-hydroxy-4-nitrophenyl)-N-(phenyl) urea, an interleukin-8B receptor antagonist, its binding and that of several analogs was measured as a function of pH. These titrations indicate that these ureas bind most strongly in their anionic form. Studies of antagonists, with different acidities, demonstrated that the greatest change in binding of each urea occurred around the pK_a of the compound being examined. The studies suggest that the increase in binding of the antagonists at higher pH is a result of the increased negative charge on the compounds rather than the effects of pH on the receptor or radioligand.