Cyclic AMP phosphodiesterases of Funaria hygrometrica

Abstract

High affinity cAMP phosphodiesterase (PDE) activity has been purified (ca 474-fold) from the chloronema cells of the moss Funaria hygrometrica. The activity in the 15 000 g supernatant was precipitated at 40-80% saturation with (NH₄)₂SO₄ and separated by DEAE-cellulose chromatography into two peaks of activity A and B with pH optima at pH 5.5 and 7.5, respectively. When rechromatographed on DEAE-cellulose, the PDE B activity redistributed into two peaks (A'and B'). The recovery of PDE activity in the latter peaks suggests a conversion of alkaline PDE into acid PDE. The phosphodiesterase activity B was further resolved by affinity chromatography on a cAMP-agarose column into PDE I and PDE II. The latter was free from nucleotidases, was Ca²⁺-dependent and showed only a high-affinity component towards cAMP as the substrate, the K_m being 11.8 ± 4.8 µ M.