Abstract
Ca2+ is considered to have an important role in cellular response to hormonal stimulation; the Ca2+dependent cyclic nucleotide phosphodiesterase (EC 3.1.4.17) present in many eukaryotic cells [I] plays an important role. In prokaryotes, phosphodiesterases have been reported but are Ca’+-independent [2,3]. The enzyme of Escherichia coli requires Fe2+ or an activator protein (M, 90 000) for its activity [2]. Here, we report the occurrence of an additional species of phosphodiesterase in the soluble fraction of E. coli. The enzyme is Ca’+-dependent and hydrolyzes both cyclic AMP and cyclic GMP. The existence of Ca’+-dependent phosphodiesterase suggests that, in prokaryotes as well as in eukaryotes, one of the roles of Ca2+ in hormonal regulation is acceleration of cyclic nucleotide degradation through the activation of the enzyme.
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