Guanylate cyclase: inhibition by light in retinal photoreceptors

Guanylate cyclase activity of retinal rod outer segments was measured by an assay procedure that minimizes the technical problems caused by the high activity of cyclic nucleotide phosphodiesterase in neural tissue. Cyclase activity in rods is significantly higher than in brain. Moreover, activity is two-fold higher in dark-adapted rods than in light-bleached rods, a sensitivity that is lost when the preparation is treated with detergent.