Cyclic nucleotide phosphodiesterase in rat parotid gland

Cyclic nucleotide phosphodiesterase was investigated in rat parotid gland to elucidate the regulatory mechanisms for the enzyme. Cyclic nucleotide phosphodiesterase activities from DEAE-cellulose column chromatography showed two main peaks. One of them was eluted with 0.15 M KCl and was fairly specific for cGMP. This enzyme was activated by calmodulin with an increase in Vmax and with no effect on Km. The other one was eluted with 0.25 M KCl and showed a higher specificity for cAMP than for cGMP. This enzyme, however, was not activated by Ca2=nd calmodulin. The presence of calmodulin and an inhibitor substance was confirmed by DEAE-cellulose column chromatography. The inhibitor substance was protein in nature and did not inhibit cAMP phosphodiesterase. These results may indicate that cGMP in rat parotid gland, which is supposed to correlate with secretion, is regulated also by phosphodiesterase through calmodulin and an inhibitor substance.