AbstractThe formylpeptide receptors from 40 × 109cells of rabbit peritoneal neutrophils have been solubilized with digitonin and partially purified by sequential fMet‐Leu‐Phe‐Sepharose affinity and wheat‐germ agglutinin agarose affinity chromatography. The binding activity of the receptor toward [3H]fNle‐Leu‐Phe is difficult to restore fully after elution of the receptor from the fMet‐Leu‐Phe‐Sepharose affinity column. A 2,000‐fold purification of the receptor from the particulate fraction is achieved with a yield of about 23%. Sodium dodecyl sulfate‐polyacrylamide gel electrophoresis and Coomasie blue or silver staining of purified receptor preparations reveal a major polypeptide with an apparent Mr (50,000‐70,000) and isoelectric points (pi 6.0 ‐ 6.5) that coincides with the polypeptide labeled by the specific affinity cross‐linking probe for formylpeptide receptor (125I‐hexapeptide). The receptor has an apparent Stokes radius of 47 å when analyzed by gel filtration chromatography. Using synthetic peptides poly(Glu‐Tyr) (4:1) as the substrates, a membrane‐associated tyrosine protein kinase activity is detected and can be solubilized by digitonin. Subsequent analysis indicates that the tyrosine kinase activity is not derived from the receptor.