THE VITAMIN A OF THE LOBSTER

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Abstract
In many crustaceans, including the lobster, the bulk of the vitamin A of the animal is concentrated in the eyes. Recently Fisher, Kon, and Thompson found that vitamin A extracted from the eyes of euphausiid Crustacea has only about 1/2 the biological potency of the same amount of the all-trans-acetate or fish liver vitamin A. These experiments show that the vitamin A of the lobster eye consists almost entirely of the hindered cis-isomer, neo-b, the precursor in the vertebrate retina of the visual pigments rhodopsin and iodopsin. This iso-mer has a low biological potency in the rat, only about 1/4 that of all-trans vitamin A. In the lobster eye it is virtually all extractable with petroleum ether, about 30% in the form of free alcohol, about 70% in the form of esters. It was identified by its absorption spectrum, as derived from measurements on crude extracts, and measured directly in purified preparations; the changes in absorption which accompany isomerization; oxidation to the corresponding retinene; and synthesis from the latter of rhodopsin. The examination of an extract of euphausiid eyes, provided by Dr. Kon, also revealed the presence of neo-b-vitamin A virtually alone. This may be the characteristic condition in the eyes of eucarid crustaceans. It is peculiar in that the neo-b-isomer, being a sterically hindered form, is ordinarily expected to be represented in any equilibrium mixture of geometric isomers in very small amount. Apparently certain crustaceans have ways of circumventing the difficulties implicit in producing and retaining this isomer, and store it in the eye virtually alone.

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