| Abstract: | A method for assessing the binding of 3H-labeled prostaglandin E1 (3H]PGE1) to cell membranes has been developed and used to study the interaction of 3H]PGE1 with membranes from cultured mammalian cells. Receptor sites were identified by correlation of the potency of a series of compounds to compete for 3H]PGE1 binding sites and to stimulate adenylate cyclase activity, by correlation of rates of binding and change in enzyme activity, and by the correspondence of 3H]PGE1-binding activity with the presence or absence of PGE1-sensitive adenylate cyclase in several clones. In clone B82, a murine L-cell, 3H]PGE1 binds with an activation energy of 14 kcal/mol to a class of sites with an affinity of 0.5 X 10(8) M-1 and a capacity of 150 fmol/mg of protein. Concentration dependence of adenylate cyclase activation by PGE1 (KD =30 nM) and kinetic analysis of 3H]PGE1 binding (k1 = 4 X 10(6) liters/mol/min, k-1 0.15/min) verify this affinity. Concentration dependence and specificity of binding and activation of adenylate cyclases in neuroblastoma clone N4TG1 and N18TG2 substantiate the method. In several clones that lack PGE1-responsive adenylate cyclase, no specific 3H]PGE1 binding is detectable. |
