Cylic nucleotide phosphodiesterase in silkworm. Characterization of cyclic GMP phosphodiesterase.

The existence of cyclic GMP phosphodiesterase (EC 3.1.4.-) was demonstrated in silkworm larva by gel filtration of the homogenate. The cyclic GMP phosphodiesterase was separated from cyclic AMP phosphodiesterases by column chromatography on hydroxyapatite and Sephadex G-200. The enzyme has a molecular weight of approx. 260 000, and optimum pH of 8.3 and a Km value of 2 muM. The enzyme is activated by 5 mM of Mg2+ and 2 mM of Mn2+. The cyclic GMP phosphodiesterase activity was greatly inhibited by low concentrations of cyclic IMP but to a lesser extent by cyclic AMP even at a high concentration. The activity was also inhibited by caffeine and theophylline.