Abstract
Frog ( Rana catesbeiana) rod outer segment membrane contains cyclic GMP phosphodiesterase (EC 3.1.4.1). Irradiation of dark-adapted rod outer segment membrane increased the enzyme activity by 5–20-fold in the presence of GTP. The phosphodiesterase in rod outer segment membrane is also activated by mixing a photo-product of 11- cis (regenerated), 9- cis or 7- cis rhodopsin which is stable at 0°C. However, neither opsin in the membrane nor all- trans retinal activates the enzyme. The phosphodiesterase in rod outer segment membrane is also activated by irradiation at −4°C. Thus, we conclude that the phosphodiesterase is activated by a common photolysis intermediate of these rhodopsin isomers, perhaps before metarhodopsin II decays.
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