Isoelectric and mass characterization of human platelet thromboxane A2/prostaglandin H2 receptors.
To further characterize the human thromboxane A2 (TXA2)/prostaglandin H2 (PGH2) receptor, preparative isoelectric focusing (IEF) was performed on solubilized platelet membranes. TXA2/PGH2 receptors, assayed by specific binding of the TXA2/PGH2 antagonist [125I]PTA-OH, were electrofocused at pH 5.6. Scatchard analysis of IEF fraction pH 5.6 revealed a 180-fold concentration of TXA2/PGH2 receptors (Bmax = 3650 +/- 228 pM/mg focused, 19 +/- 4 pM/mg unfocused) with no change in binding affinity (Kd = 47 +/- 7 nM focused, 36 +/- 14 nM unfocused). SDS-polyacrylamide gel electrophoresis of photoaffinity-labelled electrofocused receptors revealed concentration of specifically labelled proteins having molecular masses of 49,000 and 27,000 Daltons. These results suggest that the human platelet TXA2/PGH2 receptor has a pI of 5.6, molecular mass of 49,000 Daltons, and may exist as a dimer. Preparative IEF should prove useful in the eventual purification of this receptor.
Dorn
G W
GW
Department of Medicine, University of Texas Health Science Center, San Antonio 78284.
D000345:Affinity Labels; D001792:Blood Platelets / Q000032:analysis*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007526:Isoelectric Point; D008970:Molecular Weight; D011982:Receptors, Prostaglandin / Q000032:analysis*; D017482:Receptors, Thromboxane; D044244:Receptors, Thromboxane A2, Prostaglandin H2
D000345:Affinity Labels; D011982:Receptors, Prostaglandin; D017482:Receptors, Thromboxane; D044244:Receptors, Thromboxane A2, Prostaglandin H2