title: Kinetics and nucleotide specificity of a surface cAMP binding site in Dictyostelium discoideum, which is not down-regulated by cAMP.
abstract: Dictyostelium cells exhibit four types of kinetically distinct surface cAMP binding sites, the AH, AL, BS, and BSS sites, which are down-regulated during persistent stimulation with cAMP. Although most cAMP-induced responses are subject to desensitization during constant stimulation, some responses, notably the induction of post-aggregative gene expression, require persistent cAMP stimulation. The kinetics and specificity of residual cAMP-binding activity in cells treated for 4 h with micromolar cAMP were investigated. It was found that around 4000 rapidly dissociating binding sites per cell with an affinity of about 300 nM are retained after down-regulation. The nucleotide specificity of the remaining sites was very similar, but not completely identical to the AH, AL and B sites, suggesting that these sites belong to the same class of cell surface cAMP receptors and may be utilized to mediate responses requiring continuous cAMP stimulation.
authors.affiliation: Cell Biology and Genetics Unit, University of Leiden, The Netherlands.
authors.forename: M
authors.initials: M
authors.lastname: van Ments-Cohen
authors.forename: H G
authors.initials: HG
authors.lastname: Genieser
authors.forename: B
authors.initials: B
authors.lastname: Jastorff
authors.forename: P J
authors.initials: PJ
authors.lastname: Van Haastert
authors.forename: P
authors.initials: P
authors.lastname: Schaap
mesh_terms: D000818:Animals; D001665:Binding Sites; D002462:Cell Membrane / Q000378:metabolism; D000242:Cyclic AMP / Q000378:metabolism*; D004023:Dictyostelium / Q000378:metabolism*; D015536:Down-Regulation; D007700:Kinetics; D009711:Nucleotides / Q000378:metabolism; D011953:Receptors, Cyclic AMP / Q000378:metabolism
chemical_list: D009711:Nucleotides; D011953:Receptors, Cyclic AMP; D000242:Cyclic AMP