Interaction of the catalytic subunit of protein kinase A with the lung type V cyclic GMP phosphodiesterase: modulation of non-catalytic binding sites

We have previously demonstrated that the catalytic sub-unit of protein kinase A can catalyse a potent activation of partially purified Type V cyclic GMP-specific phosphodiesterase activity (Burns et al., 1992, Biochem. J. 283, 487-491). We now demonstrate that this phosphodiesterase most likely has a sub-unit mass of 90kDa, based upon 32P-cyclic GMP photo-affinity labelling, that activation of the phosphodiesterase does not require the prior binding of cyclic GMP to the phosphodiesterase, and that alkaline phosphatase can reverse the protein kinase A-dependent activation of phosphodiesterase activity. Zaprinast is a mixed inhibitor of non-activated cyclic GMP phosphodiesterase activity. However, inhibition of the protein kinase A-activated phosphodiesterase is competitive. These results suggest that protein kinase A can modulate the inhibitory effects of zaprinast via perturbations of a non-catalytic binding site.