Activation of rat lung soluble guanylate cyclase by sodium nitroprusside: effects of hemoglobin and reducing agents

A potent vasodilator, sodium nitroprusside, activated rat lung soluble guanylate cyclase about 2.0-fold; this activation was potentiated by reducing agents such as ascorbic acid and thiols, 4.5 to 9-fold. In the presence of 2-mercaptoethanol and sodium nitroprusside maximal enzymatic activity in crude enzyme preparation was evident after a lag of several minutes, after which the activity declined. Hemoglobin blocked sodium nitroprusside activation of a partially purified enzyme by causing a lag in the activation, and this inhibition was reversed by 2-mercaptoethanol. Therefore, the extent of sodium nitroprusside activation measured is affected by the concentration of hemoglobin and reducing agent present, and the activation time.