[3H]fMet-Leu-Phe binding to human neutrophil membrane proteins was shown to be inhibited by pretreatment of membranes with the histidine-preferring reagent diethylpyrocarbonate in a concentration- and time-dependent fashion. The inhibition was partially reversed by hydroxylamine and was affected by pH. The pH profile for inhibition and the partial reversibility of the inhibition by hydroxylamine are consistent with a modification of the histidine residue by diethylpyrocarbonate. The addition of unlabeled fMet-Leu-Phe to the membrane preparation prior to diethylpyrocarbonate treatment provided protection from the binding inhibition following washout of unlabeled fMet-Leu-Phe and unreacted reagent. Cells treated with diethylpyrocarbonate were inhibited in their ability to produce superoxide anions in response to fMet-Leu-Phe, but the concentration of the chemotactic factor required to obtain 50% of the response was alike for treated or untreated cells. These results suggest that a histidine residue at or near the receptor binding site for fMet-Leu-Phe is required for binding and cell activation. Neither N-acetylimidazole, an agent that preferentially reacts with tyrosine, nor acetic anhydride, which reacts with lysyl groups, affected [3H] fMet-Leu-Phe binding to plasma membrane proteins or superoxide production by intact cells. Scatchard analysis of the binding inhibition owing to diethylpyrocarbonate was consistent with a loss of receptor number rather than a change in affinity.
Diethyl Pyrocarbonate Histidine