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RICHARD W. YOUNG; A Difference between Rods and Cones in the Renewal of Outer Segment Protein. Invest. Ophthalmol. Vis. Sci. 1969;8(2):222-231.
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The renewal of protein has been studied in the retinal rods and cones of the adult frog by electron microscope autoradiography after injection of radioactive amino acids. In both classes of photoreceptor cells, the synthesis of protein is concentrated in the myoid zone of the inner segment. Newly formed (radioactive) protein is then displaced past the mitochondria of the ellipsoid zone and reaches the outer segment by flowing through the connecting structure. In rods, the labeled protein accumulates at the base of the outer segment, apparently as a component of newly assembled membranous discs, which are then gradually displaced sclerally. In cones, however, no such concentration of radioactive protein has been observed. On the contrary, protein delivered to the outer segment becomes diffusely distributed throughout that structure. TJuis, in the frog, there is a distinct difference between rods and cones in the process of protein renewal.
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