SpdA is a phosphodiesterase. (A) Purification of SpdA-His6 protein on a Ni agarose column (Qiagen). 1: Molecular weight markers, 2: Purified SpdA-His6, 3: culture sonication supernatant, 4: Column flowthrough, 5: E. coli BL21(DE3) pET::2179 cells treated with IPTG, 6: E. coli BL21(DE3) pET::2179 cells, no IPTG. (B) SpdA was incubated with the general phosphodiesterase substrate bis-pNPP. The amount of p-nitrophenol produced was measured at 405 nm. (C) Phosphodiesterase activity was measured from phosphate release after incubation of cyclic nucleotides with SpdA and CIP.