Nitric oxide (NO center dot), the only nitrogen monoxide redox form capable of activating soluble guanylyl cyclase

In the present study, we determined that of the redox forms of nitrogen monoxide, NO-, NO . and NO+, only NO . significantly- activates soluble guanylyl cyclase (GTP pyrophosphate-lyase cyclizing, EC 4.6.1.2). Neither of the NO- donors tested, Angeli's salt (Na2N2O3) or Piloty's acid (C6H5SO2NHOH), caused a change in the guanylyl cyclase activity relative to the basal activity level. Interference by other reaction products was eliminated as a possible explanation for the lack of activation. To the extent that NO+ could be stabilized in aqueous solution, by dissolution of the nitrosonium salt NOPF6 in dry organic solvent Drier to addition to the enzyme in buffer, NO+ had no effect on the activity of soluble guanylyl cyclase. The counter-ion, PF6-, had a minimal effect on the enzyme activity and, therefore was, not responsible for the lack of activation by NO+. These observations suggest that NO- is the natural activator of soluble guanylyl cyclase and is reasonably identical with endothelium-derived relaxing factor, the physiological regulator of soluble guanylyl cyclase activity.