Comparison between guanylate and adenylate cyclase active sites. Monomer B of the guanylate cyclase catalytic domain was superimposed onto the C2 domain of mammalian adenylate cyclase (PDB ID: 1CJU) . Residues and structural elements involved in catalysis and nucleotide recognition are shown. A) Comparison of guanylate and adenylate cyclase catalytic residues. B) Comparison of guanylate and adenylate cyclase base recognition residues. Side chains and structural elements from the guanylate cyclase and adenylate cyclase catalytic domains are colored green and grey, respectively. The nucleotide 2',3'-dideoxyadenosine triphosphate (ddATP) and the two Mg2+ ions are from 1CJU. Non-carbon atoms are colored as follows: phosphorus, orange; oxygen, red; nitrogen, blue; sulfur, yellow; arsenic, violet; magnesium, white.