Characterization of guanylate cyclase in frog retina using nitrosoguanidine and superoxide dismutase

Guanylate cyclase in the membrane fraction of rod outer segments (ROS-membrane) from the frog retina showed an extremely high activity but had no responsiveness to NaN(3) (+catalase), nitrosoguanidine or superoxide dismutase. These compounds, however, markedly activated the enzyme in a soluble fraction from the retina. Although the activation of the soluble guanylate cyclase by superoxide dismutase was completely repressed by KCN, diethyldithiocarbamate and hemoglobin, these drugs had no effect on the basal enzyme activity in ROS-membrane. Guanylate cyclases in opsin membrane and retinoids-depleted ROS-membrane also showed no responsiveness to nitrosoguanidine and superoxide dismutase. These results indicate that there are two types of guanylate cyclase (soluble type and ROS-membrane type, respectively) in the frog retina, defined in terms of their responsiveness to nitrosoguanidine and superoxide dismutase.