title: Physicochemical properties of the N-formyl peptide receptor on human neutrophils.
abstract: In order to investigate the physicochemical properties of the N-formyl peptide receptor of human neutrophils, the receptor was specifically and covalently labeled with an iodinated, photoactivatable derivative of the chemotactic hexapeptide, N-formyl-norleucylleucyl- phenylalanyl-norleucyl-[125I]iodotyrosyl-N epsilon-(6- (4'-azido-2'-nitrophenylamino) hexanoyl)-lysine. After labeling isolated neutrophil membranes, the receptor was extracted with Triton X-100, digitonin, or octyl glucoside and subjected to gel filtration on a calibrated Ultrogel AcA 34 column. The Triton X-100- and digitonin-extracted receptor eluted as single molecular species, with Stokes radii of 40 and 33 A, respectively. This material was subjected to further physicochemical analysis. When octyl glucoside-extracted material was gel-filtered, a second peak containing specifically labeled material eluted in the void volume. Subsequent sodium dodecyl sulfate-polyacryl-amide amide gel electrophoresis analysis indicated that this species was the result of disulfide bonded aggregates containing the monomeric species. Sedimentation equilibrium analysis was carried out in H2O and D2O/H2O mixtures, yielding an apparent molecular mass of 63,000 daltons for both Triton X-100- and digitonin-extracted receptor. This agrees closely with the reduced sodium dodecyl sulfate-polyacrylamide gel electrophoretic value of 50,000-60,000 daltons, indicating that the receptor extracted from unstimulated membranes is monomeric in these detergents. From the sedimentation equilibrium data, the partial specific volume (v) and frictional ratio (f/f0) were calculated. The v is high in both Triton X-100 (0.880) and digitonin (0.829), indicating that the receptor may be associated with tightly bound endogenous lipid or that it is a hydrophobic membrane protein. This latter likelihood is further supported by the quantitative extraction of receptor into Triton X-114 by a phase-separation method. The frictional ratio of 1.1-1.3 is consistent with an elongated globular protein having an axial ratio of approximately 3:1. This in conjunction with the Stokes radius of 40 A would indicate that the receptor is capable of spanning the 35-40-A nonpolar center of the lipid bilayer. The state of the receptor in situ is discussed.
mesh_terms: D000345:Affinity Labels; D001386:Azides / Q000378:metabolism; D002850:Chromatography, Gel; D003902:Detergents; D006023:Glycoproteins / Q000302:isolation & purification; D006801:Humans; D009504:Neutrophils / Q000032:analysis*; D009842:Oligopeptides / Q000378:metabolism; D044042:Receptors, Formyl Peptide; D011971:Receptors, Immunologic / Q000302:isolation & purification*; D012995:Solubility
chemical_list: D000345:Affinity Labels; D001386:Azides; D003902:Detergents; D006023:Glycoproteins; D009842:Oligopeptides; D044042:Receptors, Formyl Peptide; D011971:Receptors, Immunologic; C036764:NPH-peptide