Studies in vitamin A. 25. Visual pigments in tadpoles and adult frogs

Abstract
Wald reported (Harvey Lect. 41: 117. 1946) that tadpoles of Rana catesbiana contain vit. A2 but that after metamorphosis the adults contain vit. A1 only. Tadpoles of R. esculenta and R. temporaria were shown to have vit. A1 only. The visual pigment in both cases was rhodopsin. The occurrence of vit. A2 was reviewed and an endeavor was made to reconcile the many apparently conflicting reports. It is concluded that vit. A2 may result from (a) preformed vit. A2 in the diet (b) the conversion of beta-carotene and other provit. to vit. A2, and (c) the conversion of a specific provit. A2 which might be an animal carotenoid such as astaxanthin.
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