Effects of CuCl2 on the hydrolysis of cyclic GMP and cyclic AMP by the activator-dependent cyclic nucleotide phosphodiesterase from bovine heart.

CuCl2 non-competitively inhibited the hydrolysis of cyclic GMP and cyclic AMP by the activator-dependent phosphodiesterase from bovine heart in the presence of 5 mM Mg2+, 10 muM Ca2+ and phosphodiesterase activator with Ki values of approximately 2 muM for both substrates. CuCl2 inhibition was also non-competitive with Mg2+, Ca2+ and phosphodiesterase activator. Dialysis demonstrated that CuCl2 inhibition is reversible. Treatment of the enzyme with p-hydroxymercuribenzoate resulted in the loss of enzyme activity, suggesting the presence of sulfhydryl groups essential for enzyme activity. The inhibitory activity of CuCl2 was not additive with that of p-hydroxymercuribenzoate, therefore CuCl2 may inhibit enzyme activity by binding to one or more essential sulfhydryl groups. CuCl2 also inhibited the hydrolysis of cyclic AMP by the cyclic AMP-specific phosphodiesterase from bovine heart with an I50 value of 18 muM. Several effects of Cu2+ are discussed which have been noted in other studies and might be due, in part, to changes in cyclic nucleotide levels following alterations in phosphodiesterase activity.