Ligand-induced modification of a surface cAMP receptor of Dictyostelium discoideum does not require its occupancy

B. E. Snaar-Jagalska, P. N. Devreotes, P. J.M. Van Haastert

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11 Scopus citations


In Dictyostelium discoideum amoebae, cAMP-induced phosphorylation of the surface cAMP receptor is associated with a discrete transition in its electrophoretic mobility. The native and modified forms of the receptor are designated R and D (M(r) = 40,000 and 43,000). The relationship of the number of receptors which are modified as a function of the receptors which bind cAMP was investigated. Modification was assessed by determining the amounts of R and D forms in Western blots which detect all receptors whether or not they are exposed on the surface. Cyclic AMP or the analog, adenosine 3',5'-monophosphorothioate ((R(p))-cAMPS), induced a loss of cAMP-binding activity (down-regulation), which was not accompanied by a loss of the receptor protein. About 60% of the receptors do not bind cAMP in the absence of Ca2+ and are unmasked by 10 mM Ca2+. However, the fraction of receptors which are modified in response to cAMP is equal in the absence or presence of Ca2+. (R(p))-cAMPS induces down-regulation (50%) but not modification. Addition of cAMP, following down-regulation by (R(p))-cAMPS, causes all receptors to be modified. cAMP-induces both down-regulation (80%) and modification. Modification is more readily reversed than down-regulation: 30 min after removal of cAMP, receptors remain down-regulated (57%) but are found in the R form. All receptors shift to the D form when cAMP is readded to the cells. These results indicate that exposed, as well as cryptic and down-regulated receptors, are modified in response to the cAMP stimulus.

Original languageEnglish (US)
Pages (from-to)897-901
Number of pages5
JournalJournal of Biological Chemistry
Issue number2
StatePublished - 1988
Externally publishedYes

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology


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