title: Photoaffinity labelling of the human platelet thromboxane A2/prostaglandin H2 receptor.
abstract: The synthesis, binding and photoincorporation of a thromboxane A2/prostaglandin H2 (TXA2/PGH2) analog (9,11-dimethylmethano-11,12-methano-16-(3-[125I]iodo-4-azidophenyl )-13,14- dihydro-13-aza-15 alpha beta-omega-tetranor-TXA2) [( 125I]PTA-Azido) to washed human platelets was characterized. Kinetic analysis of the binding of [125I]PTA-Azido at 30 degrees C yielded a k1 of 1.83.10(7) M-1.min-1 and k -1 of 0.195 min-1, Kd = k -1/k1 = 11 nM. Incubation of washed human platelets with [125I]PTA-Azido followed by photolysis resulted in the radiolabelling of a number of platelet proteins as assessed by SDS-PAGE autoradiography. The radiolabelling of three of these protein bands could be either uniformly blocked or reduced with a series of structurally dissimilar TXA2/PGH2 receptor antagonists or agonists and corresponded to proteins with a molecular mass of 43, 39 and 27 kDa. In addition, the incorporation of [125I]PTA-Azido into the three proteins was stereoselectively blocked by a pair of optically active stereoisomers that are TXA2/PGH2 receptor antagonists. Two-dimensional gel electrophoresis indicated that the 43 kDa protein possessed a pI value of 5.6 and that the 27 kDa protein exists in at least three isoforms with pI values of 4.9, 5.1 and 5.3. The labelling pattern was not altered by a mixture of proteinase inhibitors. The data suggest that one or more of these specifically radiolabelled proteins may represent the human platelet TXA2/PGH2 receptor.
authors.affiliation: Department of Cell and Molecular Pharmacology, Medical University of South Carolina, Charleston 29425.
authors.forename: D E
authors.initials: DE
authors.lastname: Mais
authors.forename: C
authors.initials: C
authors.lastname: Yoakim
authors.forename: Y
authors.initials: Y
authors.lastname: Guindon
authors.forename: J W
authors.initials: JW
authors.lastname: Gillard
authors.forename: J
authors.initials: J
authors.lastname: Rokach
authors.forename: P V
authors.initials: PV
authors.lastname: Halushka
mesh_terms: D000345:Affinity Labels / Q000138:chemical synthesis*; D001386:Azides / Q000097:blood / Q000138:chemical synthesis*; D001792:Blood Platelets / Q000378:metabolism*; D015180:Electrophoresis, Gel, Two-Dimensional; D006801:Humans; D066298:In Vitro Techniques; D007700:Kinetics; D010777:Photochemistry; D011449:Prostaglandin Endoperoxides / Q000097:blood*; D011463:Prostaglandins H / Q000097:blood*; D011869:Radioligand Assay; D011982:Receptors, Prostaglandin / Q000378:metabolism*; D017482:Receptors, Thromboxane; D044244:Receptors, Thromboxane A2, Prostaglandin H2; D013928:Thromboxane A2 / Q000031:analogs & derivatives* / Q000097:blood* / Q000138:chemical synthesis
chemical_list: D000345:Affinity Labels; D001386:Azides; D011449:Prostaglandin Endoperoxides; D011463:Prostaglandins H; D011982:Receptors, Prostaglandin; D017482:Receptors, Thromboxane; D044244:Receptors, Thromboxane A2, Prostaglandin H2; C060266:9,11-dimethylmethano-11,12-methano-16-(3-iodo-4-azidophenyl)-13,14-dihydro-13-aza-15-tetranorthromboxane A2; D013928:Thromboxane A2