Enzyme-inhibitor interactions as a basis for heterogeneity of extracellular cyclic AMP phosphodiesterases in Dictyostelium discoideum

Abstract

We have previously characterized three forms of cyclic-AMP phosphodiesterase obtained after dithiothreitol activation of the enzyme from the extracellular medium during late vegetative growth of Dictyostelium discoideum (Toorchen, D. and Henderson, E.J. (1979) Biochem. Biophys. Res. Commun. 87, 1168–1175). This communication presents evidence supporting the earlier hypothesis that the observed heterogeneity of enzyme species is due to formation of complexes between an endogenous inhibitor protein and a common catalytic polypeptide. Dithiothreitol inactivates the inhibitor, but does not cause its release from the catalytic unit. Additional evidence is presented for the presence of a similar catalytic polypeptide in the extracellular phosphodiesterase produced during the first 8 h of developmetn, except that this species is a phosphoprotein.