Hydrogen sulfide stimulates the catalytic activity of a heme-regulated phosphodiesterase from Escherichia coli (Ec DOS)

► Catalysis by Ec DOS, an oxygen-sensor enzyme, is markedly increased by Na2S. ► The SH−-modified heme iron complexes, such as Fe(III)-SH− and Fe(II)-O2 complexes, represent the active species for Na2S-induced catalysis. ► Modification of Cys residues in the catalytic domain by SH− also significantly contributes to the catalytic enhancement by Na2S.