In vitro interaction between hydroxyurea and heme of sGC. (A) Sodium nitrite (0.001-10 mM) did not induce cGMP production of purified sGC as measured by radioimmunoassay. (B) Using tri-iodine–based reductive chemiluminescence assay, we measured the formation of the iron-nitrosyl complex during treatment of purified sGC with hydroxyurea and ProliNONOate. The numbers above columns represent percentage of conversion of deoxy-heme to the iron-nitrosyl complex (n = 3). Values are means (± SEM).