Activation of guanylate cyclase in cerebral cortex of rat by hydroxylamine.

Hydroxylamine actived guanylate cyclase in particulate fraction of cerebral cortex of rat. Activation was most remarkable in crude mitochondrial fraction. When the crude mitochondrial fraction was subjected to osmotic shock and fractionated, guanylate cyclase activity recovered in the subfractions as assayed with hydroxylamine was only one-third of the starting material. Recombination of the soluble and the particulate fractions, however, restored guanylate cyclase activity to the same level as that of the starting material. When varying quantities of the particulate and soluble fractions were combined, enzyme activity was proportional to the quantity of the soluble fraction. Heating of the soluble or particulate fraction at 55 degrees for 5 min inactivated guanylate cyclase. The heated particulate fraction markedly activated guanylate cyclase activity in the native soluble fraction, while the heated soluble fraction did not stimulate enzyme activity in the particulate. The particulate fraction preincubated with hydroxylamine at 37 degrees for 5 min followed by washing activated guanylate cyclase activity in the soluble fraction in the absence of hydroxylamine. Further fractionation of the crude mitochondrial fraction revealed that the factor(s) needed for the activation by hydroxylamine is associated with the mitochondria. The mitochondrial fraction of cerebral cortex activated guanylate cyclase in supernatant of brain, liver, or kidney in the presence of hydroxylamine. The mitochondrial fraction prepared from liver or kidney, in turn, activated soluble guanylate cyclase in brain. Activation of guanylate cyclase by hydroxylamine was compared with that of sodium azide. Azide activated guanylate cyclase in the synaptosomal soluble fraction, while hydroxylamine inhibited it. The particulate fraction preincubated with azide followed by washing did not stimulate guanylate cyclase activity in the absence of azide. The activation of guanylate cyclase by hydroxylamine is not due to a change in the concentration of the substrate GTP, Addition of hydroxylamine did not alter the apparent Km value of guanylate cyclase for GTP. Guanylate cyclase became less dependent on manganese in the presence of hydroxylamine. Thus the activation of guanylate cyclase by hydroxylamine is due to the change in the Vmax of the reaction.