Incorporation of [ 3H]vitamin A into rhodopsin in light- and dark-adapted frogs

Abstract

When light- or dark-adapted frogs are injected with [ 3H]vitamin A acetate, the early time course of incorporation of the precursor into rhodopsin is marekedly different for the two lighting conditions. Frogs injected and kept in the light incorporate [ 3H]vitamin A into rhodopsin within 2 hr. In contrast, frogs injected and kept in the dark show very little labeling of rhodopsin prior to 12 hr. It appears that in light-adapted frogs, two routes of incorporation of vitamin A into rhodopsin are possible: (1) a random regeneration of rhodopsin when 11- cis-retinaldehyde combines with vacant opsin molecules in the outer segment. (2) by incorporation of 11- cis-retinaldehyde into newly forming discs at the base of the outer segment. In dark-adapted frogs, only the second process appears to occur. The time course of these two processes appears to be influenced by the activity of the pigment epithelium in light and dark.