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

Abstract

In the presence of 10 μM Ca 2+ and 5 mM Mg 2+ (or 0.25 mM Mg 2+), the addition of 100 μM Zn 2+, Ni 2+, Co 2+, Fe 2+, Cu 2+ or 1 mM Mn 2+ resulted in varying degrees of stimulation or inhibition of 10 −6 M cyclic GMP and cyclic AMP hydrolysis by the activator-dependent cyclic nucleotide phosphodiesterase from bovine heart in the absence or presence of phosphodiesterase activator. The substrate specificity of the enzyme was altered under several conditions. The addition of Zn 2+ in the presence of 5 mM Mg 2+ and the absence of activator resulted in the stimulation of cyclic GMP hydrolysis over a narrow substrate range while reducing the V 65% due to a shift in the kinetics from non-linear with Mg 2+ alone to linear in the presence of Zn 2+ and Mg 2+. Zn 2+ inhibited the hydrolysis of cyclic GMP and cyclic AMP in the presence of activator with K i values of 70 and 100 μM, respectively. Zn 2+ inhibition was non-competitive with substrate, activator and Ca 2+ but was competitive with Mg 2+. In the presence of 10 μM Ca 2+ and activator, a K i of 15 μM for Zn 2+ vs. Mg 2+ was noted in the hydrolysis of 10 −6 M cyclic GMP. Several effects of Zn 2+ are discussed which have been noted in other studies and might be due in part to changes in cyclic nucleotide levels following phosphodiesterase inhibition.