Kinetics and nucleotide specificity of a surface cAMP binding site in Dictyostelium discoideum, which is not down-regulated by cAMP.
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.
van Ments-Cohen
M
M
Cell Biology and Genetics Unit, University of Leiden, The Netherlands.
Genieser
H G
HG
Jastorff
B
B
Van Haastert
P J
PJ
Schaap
P
P
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
D009711:Nucleotides; D011953:Receptors, Cyclic AMP; D000242:Cyclic AMP