ZINC INTERACTIONS AND CONSERVED MOTIFS OF THE CGMP-BINDING CGMP-SPECIFIC PHOSPHODIESTERASE SUGGEST THAT IT IS A ZINC HYDROLASE

cGMP-binding cGMP-specific phosphodiesterase (cG-BPDE) binds tightly t o a Zn2+-chelate column (Francis, S. H., and Corbin, J. D. (1988) Meth ods Enzymol. 159, 722-729). Using three different approaches, Zn2+ is now shown to bind to cG-BPDE, and the K-d is determined to be similar to 0.5 mu m, with a binding stoichiometry of similar to 3 mol of Zn2+/ mol of monomer. A similar concentration range of Zn2+ (0.05-1 mu m Zn2 +) also supports phosphodiesterase (PDE) catalytic activity. The Zn2binding to cG-BPDE is not diminished by, nor is catalysis supported by , relatively high concentrations of CU2+, Cd2+, Ca2+, or Fe2+. Neither cGMP nor 3-isobutyl-1-methylxanthine affects Zn2+ binding under the c onditions used. Mn2+, Co2+, or Mg2+ supports catalysis, but only at si gnificantly higher concentrations (4-, 15-, and 250-fold, respectively ) than that required for Zn2+. Two tandem amino acid sequences, which are conserved in the catalytic domains of all characterized mammalian PDEs, resemble the single sequence motif that has been shown to coordi nate Zn2+ in the catalytic sites of Zn2+ hydrolases such as thermolysi n.