A cAMP-binding protein from Dictyostelium discoideum regulates mammalian protein kinase

Abstract

A cAMP-binding protein isolated from the cytosol of Dictyostelium discoideum was partially purified. The protein binds cAMP maximally at pH 5–7; its KD for cAMP is in the nanomolar range and the specificity for cAMP is high; the molecular weight is approximately 42,000. This cAMP-binding protein is not found in vegetative amoebae; it appears during the first two hours of development. The protein inhibits the activity of the purified catalytic subunit of bovine cAMP-dependent protein kinase in the absence, but not in the presence, of cAMP. It is suggested that the cAMP-binding protein, isolated from Dictyostelium, is either the regulatory subunit of cAMP-dependent protein kinase or the product of the partial degradation of such a regulatory subunit.