A stimulating effect of guanyl nucleotides on the rat-liver soluble cyclic GMP high-affinity phosphodiesterase activity.

The high affinity (low Km) cyclic GMP phosphodiesterase (PDE) is activated by GTP, while the cyclic AMP PDE is not. GTP and its hydrolysis-resistant analogue, guanylylimidodiphosphate (GppNHp), display a half-maximal stimulating effect at almost the same concentration (5 X 10(-6) M). The GTP stimulating effect is not observed when the socalled cyclic GMP low affinity (high Km) PDE is operative. GTP cooperates with the increase of the substrate concentration on removing the IBMX inhibitory effect. The isolation through a classical chromatographic procedure on a DEAE-cellulose column, of a PDE fraction specific for cyclic GMP, results in the loss of the GTP stimulating effect.